Clean Water: Next Generation Technologies (Advances in Science, Technology & Innovation) [2024 ed.] 3031482271, 9783031482274

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Advances in Science, Technology & Innovation IEREK Interdisciplinary Series for Sustainable Development

Khouloud Jlassi · Mehmet A. Oturan · Ahmad Fauzi Ismail · Mohamed Mehdi Chehimi Editors

Clean Water: Next Generation Technologies

Advances in Science, Technology & Innovation IEREK Interdisciplinary Series for Sustainable Development Editorial Board Anna Laura Pisello, Department of Engineering, University of Perugia, Italy Dean Hawkes, University of Cambridge, Cambridge, UK Hocine Bougdah, University for the Creative Arts, Farnham, UK Federica Rosso, Sapienza University of Rome, Rome, Italy Hassan Abdalla, University of East London, London, UK Sofia-Natalia Boemi, Aristotle University of Thessaloniki, Greece Nabil Mohareb, Faculty of Architecture—Design and Built Environment, Beirut Arab University, Beirut, Lebanon Saleh Mesbah Elkaffas, Arab Academy for Science, Technology and Maritime Transport, Cairo, Egypt Emmanuel Bozonnet, University of La Rochelle, La Rochelle, France Gloria Pignatta, University of Perugia, Italy Yasser Mahgoub, Qatar University, Qatar Luciano De Bonis, University of Molise, Italy Stella Kostopoulou, Regional and Tourism Development, University of Thessaloniki, Thessaloniki, Greece Biswajeet Pradhan, Faculty of Engineering and IT, University of Technology Sydney, Sydney, Australia Md. Abdul Mannan, Universiti Malaysia Sarawak, Malaysia Chaham Alalouch, Sultan Qaboos University, Muscat, Oman Iman O. Gawad, Helwan University, Helwan, Egypt Anand Nayyar , Graduate School, Duy Tan University, Da Nang, Vietnam Series Editor Mourad Amer, International Experts for Research Enrichment and Knowledge Exchange (IEREK), Cairo, Egypt

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Khouloud Jlassi · Mehmet A. Oturan · Ahmad Fauzi Ismail · Mohamed Mehdi Chehimi Editors

Clean Water: Next Generation Technologies

Editors Khouloud Jlassi Center for Advanced Materials Qatar University Doha, Qatar Ahmad Fauzi Ismail Advanced Membrance Technology Reserach Center (AMTEC) Universiti Teknologi Malaysia Johor Bahru, Johor, Malaysia

Mehmet A. Oturan Francilien Institute of Applied Sciences Gustave Eiffel University Marne-La-Vallée, France Mohamed Mehdi Chehimi ITODYS Lab, Université Paris Cité & CNRS (UMR 7086) Paris, France

ISSN 2522-8714 ISSN 2522-8722  (electronic) Advances in Science, Technology & Innovation IEREK Interdisciplinary Series for Sustainable Development ISBN 978-3-031-48227-4 ISBN 978-3-031-48228-1  (eBook) https://doi.org/10.1007/978-3-031-48228-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Preface

In recent decades, the social development, economic growth, booming population, and especially climate change, impact on water availability, and hydrological risks have caused aggravated water pollution, making clean water production an urgent issue to be addressed. For this reason, we, Editors, have decided to review, and compile fundamental aspects, as well as promising applications of systems designed for clean water production, in a single book. Moreover, the book proposal has been prepared considering the United Nations’ 17 Sustainable Development Goals (SDGs). In this regard, we thank all Springer editors who welcomed the book proposal, and supported us to complete it. We are grateful to our contributors who accepted, despite being heavily burdened, to provide broad coverage of topics, spanning from water recovery from the dew and light rain, to molecular recognition of pollutants, and their removal by emerging water treatment processes. Larger scale water treatment is tackled with bioreactor and electrocoagulation systems. The combination of advanced fundamental research and demonstration of proofs of concepts led to the publication of numerous patents and modern technological developments. In Chapter “Emerging Water Recovery Processes from Dew and Light Rain”, Beysens & Muselli report strategies for water harvesting from the dew and light rain, with emphasis on superhydrophobic surfaces. François Zaviska (Chapter “Capacitive Deionization: A Promising Water Treatment and Desalination Technology”) reports on deionization techniques for the purpose of water desalination. In Chapters “Hydrophobic Ceramic Hollow Fiber Membrane: Fabrication and Potential Use in Membrane Distillation for Desalination”, “Metal–Organic Frameworks as Emerging Materials for Desalination”, and “Nanofiber-Based Forward Osmosis Membrane for Desalination”, researchers from the group of Ahmed Fauzi Ismail shared their knowledge of membrane technology for water purification, particularly water desalination with smart materials. Water treatment requires screening of the pollutants contained in water. The recent trends point to the application of smart, portable sensors for on-site sensing of pollutants. The focus is on wearable smart devices (Fourati & co-workers, Chapter “Recent Progress and Trends in Water Pollutant Monitoring with Smart Devices”). Sensors are also very important in fish farming; this ensures obtaining safe farmed species, as discussed by Ktari & Kalfat (Chapter “Water Contamination in Fish Farms: Electrochemical Contribution”). Pollutant signaling is important, but action is then required for the removal of toxic compounds. Organics are now very frequently destroyed and mineralized by advanced oxidative processes (AOP); much is said herein about the Fenton reaction and its modern variants, as thoroughly discussed by the team of P. V. Nidheesh (Chapter “Advanced Oxidation Processes”), N. Oturan & M. A. Oturan (Chapter “Fenton-Related Advanced Oxidation Processes (AOPs) for Water Treatment”), and Ganiyu and Martínez-Huitle (Chapter “Prospects and Challenges of Electrooxidation and Related Technologies for the Removal of Pollutants from Contaminated Water and Soils”). Nevertheless, AOPs and other treatment processes require the development of efficient catalysts whose performance is based, in part, on their size and even dispersion into and on the surface of mesoporous silica and biochar supports, among others (Snoussi et al., Chapter “Porous Composite Catalysts for the Removal of Water Organic Pollutants: A Materials Chemist Perspective”). Another highly toxic pollutant is chromium VI, which requires efficient (bio)electrochemical and photocatalytic methods to reduce it to chromium III (Bo Jiang, Chapter “Advanced Treatment of Water Polluted by Hexavalent v

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Preface

Chromium”). The team of Bruno Tassin (Chapter “Microplastic and Nanoplastic Removal Efficiency with Current and Innovative Water Technologies”) discusses the concerns and possible problem solving of microplastics and nanoplastics, e.g., via flocculation-filtration or advanced strategies such as photocatalysis, anodic oxidation, or enzymatic degradation. In Chapter “Membrane Bioreactor for Sewage Treatment”, Yogarathinam et al. discuss sewage treatment using a membrane bioreactor. This technique is based on the combination of biodegradation and membrane separation; it is reported to be highly efficient for landfill leachate and wastewater. In Chapter “Electrocoagulation”, the team of Emna Selmane reviews the fundamentals and applications of electrocoagulation in municipal wastewater treatment. This process rests on the combination of coagulation, flotation, sedimentation, and electrochemical oxidation. In Chapter “Removal of Organochlorine Pesticides from Soil and Water”, Carmen Domínguez and co-workers tackle the legacy of lindane, an organochlorinated pesticide in soil and water. It is found all over the world although it has been banned. However, it is ranked among persistent organic pollutants, therefore making the task challenging for its elimination; this is what is discussed by the authors. We close the book with a contribution on shortlisted recent patents and industrial devices for producing clean water (Aiman Eid Al-Rawajfeh et al., Chapter “Recent Patents and Modern Industrial Devices for Clean Water”). Desalination is on focus for large supply, but the technology is energy consuming, hence the necessity for new technologies, for example, solar and other renewablepowered desalination processes. The costs of several technologies are provided, compared, and discussed. We trust this book will be valuable for academics, technologists, students, and newcomers in the field, as it has contributions from experts in the field of clean water production and water treatment. We thank our authors very warmly for sharing their knowledge and providing numerous problem-solving strategies for clean water. They clearly demonstrate that SDG 6 relevant to “Clean water and sanitation” can be addressed only in a holistic way, gathering experienced scientists at the crossroads of various domains such as environmental science, materials chemistry and engineering, chemical science and engineering, nanotechnology, separation science, sensors, and actuators, to name but a few. However, emerging concepts need also to be scaled up, and going above technology readiness level TRL 3–4 is tedious and requires much time and energy from academic researchers. Moreover, gathering academics, industrials, and policy makers to achieve, hand in hand, the goal of clean water for all, is the hidden part of the iceberg, given the immense management duties it requires for making the right decisions at the right time. We, Editors, anticipate the new book will open new horizons in clean water production and will be a source of inspiration for the next generation of clean water technology researchers. Doha, Qatar Marne-La-Vallée, France Johor, Malaysia Paris, France

Khouloud Jlassi Mehmet A. Oturan Ahmad Fauzi Ismail Mohamed Mehdi Chehimi

Contents

Emerging Water Recovery Processes from Dew and Light Rain. . . . . . . . . . . . . . . . . 1 Daniel Beysens and Marc Muselli Capacitive Deionization: A Promising Water Treatment and Desalination Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Myriam Tauk, Marc Cretin, Mikhael Bechelany, Philippe Sistat and Francois Zaviska Hydrophobic Ceramic Hollow Fiber Membrane: Fabrication and Potential Use in Membrane Distillation for Desalination . . . . . . . . . . . . . . . . . . . 41 Mohamed Farag Twibi, Saber Abdulhamid Alftessi, Mohd Hafiz Dzarfan Othman, Mohd Ridhwan Bin Adam, Ahmad Fauzi Ismail, Husein D. Meshreghi, Jamal Amar Eljurni, Mukhlis A. Rahman and Juhana Jaafar Metal–Organic Frameworks as Emerging Materials for Desalination. . . . . . . . . . . . 57 Noor Fadilah Yusof, Nur Zhatul Shima Yahaya, Mohd Hafiz Dzarfan Othman, Juhana Jaafar, A. F. Ismail and Mukhlis A Rahman Nanofiber-Based Forward Osmosis Membrane for Desalination. . . . . . . . . . . . . . . . . 69 Atikah Mohd Nasir, Nurafidah Arsat, Nurul Natasha Mohammad Jafri, Juhana Jaafar, Ahmad Fauzi Ismail, Mohd Hafiz Dzarfan Othman and Mukhlis A. Rahman Recent Progress and Trends in Water Pollutant Monitoring with Smart Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Sohayb Khaoulani, Chouki Zerrouki and Najla Fourati Water Contamination in Fish Farms: Electrochemical Contribution. . . . . . . . . . . . . 95 Nadia Ktari and Rafik Kalfat Advanced Oxidation Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 P. K. Rakhi, Komal Mishra, Jaimy Scaria, M. Suresh Kumar and P. V. Nidheesh Fenton-Related Advanced Oxidation Processes (AOPs) for Water Treatment. . . . . . 117 Nihal Oturan and Mehmet A. Oturan Prospects and Challenges of Electrooxidation and Related Technologies for the Removal of Pollutants from Contaminated Water and Soils. . . . . . . . . . . . . . 145 Soliu O. Ganiyu and Carlos A. Martínez-Huitle Porous Composite Catalysts for the Removal of Water Organic Pollutants: A Materials Chemist Perspective. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Youssef Snoussi, Arvind K. Bhakta, Mengqi Tang, Khouloud Jlassi and Mohamed M. Chehimi

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Advanced Treatment of Water Polluted by Hexavalent Chromium. . . . . . . . . . . . . . 183 Bo Jiang Microplastic and Nanoplastic Removal Efficiency with Current and Innovative Water Technologies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199 Minh Trang Nguyen, Amna Abdeljaoued, Jean-Sébastien Barbier, Rachid Dris, Johnny Gasperi, Yicalo-Eyob Tecle, Patrik Stenner, Nicolas Vogel and Bruno Tassin Membrane Bioreactor for Sewage Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 Lukka Thuyavan Yogarathinam, Ahmad Fauzi Ismail and Pei Sean Goh Electrocoagulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 Emna Selmane Bel Hadj Hmida, Houyem Abderrazak and Takoua Ounissi Removal of Organochlorine Pesticides from Soil and Water. . . . . . . . . . . . . . . . . . . . 239 Carmen M. Domínguez, Alicia Checa-Fernandez, Raúl García-Cervilla, David Lorenzo, Salvador Cotillas, Sergio Rodríguez, Jesús Fernández and Aurora Santos Recent Patents and Modern Industrial Devices for Clean Water. . . . . . . . . . . . . . . . 267 Aiman Eid Al-Rawajfeh, Ghada Al Bazedi, Muhammad Kashif Shahid, Hosam Al-Itawi and Jun Wei Lim Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Contents

Emerging Water Recovery Processes from Dew and Light Rain Daniel Beysens and Marc Muselli

Abstract

Water recovery from dew is one of the smartest methods of water supply in remote places, particularly deserts. It relies on modern surface science and technology for the design of super hydrophobic tilted surfaces. The chapter will first summarize the physical, chemical and biological characteristics of dew. Then past and present methods of recovery of water from dew will be discussed together with recent findings on the design of patterned super hydrophobic surfaces and their uses for dew water recovery. Harvesting light rainfalls, which share with dew many physical, chemical and biological characteristics, is also considered in this chapter.

Keywords

Dew water · Dew harvesters · Light rain · Dew physical characteristics · Light rain physical characteristics ·  Dew chemical characteristics · Light rain chemical characteristics · Dew biological characteristics ·  Light rain biological characteristics

D. Beysens (*)  Physique et Mécanique des Milieux Hétérogènes, CNRS, ESPCI Paris - PSL University, Sorbonne Université, Sorbonne Paris Cité, 10 rue Vauquelin, 75005 Paris, France e-mail: [email protected] D. Beysens · M. Muselli  OPUR, 2 rue Verderet, 75016 Paris, France M. Muselli  Università di Corsica Pasquale Paoli, Avenue du 9 septembre, 20250 Corte, France

1 Introduction In the context of global warming and the increasing need for fresh and potable water, alternate sources can be of valuable help to replace and/or augment the classical sources (spring water, rivers, lakes, underground water, etc.). The atmosphere contains approximately the equivalent of 12,900 km3 of liquid water under gaseous, liquid and solid phases (Oki and Kanae 2006), making it a prime source for exploitation. Rain, when it is frequent, can be collected. Another source is concerned with the condensation of the atmospheric water vapor, which in nature is dew. Although dew can be condensed by active cooling devices needing external energy (see e.g. Khalil et al. 2016; Jarimi et al. 2020), this chapter rather focuses on natural dew whose yield is enhanced by specific materials and condenser forms. Natural dew is indeed a passive, energy-free water extraction process taking benefit from the deficit of radiative exchange between the condensing materials and atmosphere. The deficit is able to cool the materials such as to reach the atmosphere dew point where the vapor contained in the surrounding humid air condenses. This process is facilitated at night when solar radiation does not heat the materials and the atmosphere is cooler, with a temperature closer to its dew point temperature. Usually a few K cooling with respect to ambient air is then enough to reach the dew point temperature. This process can be optimized with respect to the meteorological conditions by using specific condenser shapes and new materials that enhance device cooling and water collection. The technology is simple and robust and involves only free passive energy. In addition, water is in general of good chemical and biological quality. When needed, further treatments to make water potable are therefore light and are not costly. The only limitation of the volume of condensed water is related to the available cooling energy, which does not go above 100 W m−2. The maximum expected dew yield is thus in the order of 1 L m−2

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 K. Jlassi et al. (eds.), Clean Water: Next Generation Technologies, Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-031-48228-1_1

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D. Beysens and M. Muselli

(1 mm; Beysens 2018). Several very large dew condensers (dew plants) have been erected so far, e.g. in Morocco (Clus et al. 2013) and in India (Sharan 2006; Sharan et al. 2011, 2017). Rain is already condensed water. Rain naturally falls and can be easily collected. Light rains, mostly ignored, have however in common with dew a number of characteristics concerning essentially collection, chemistry and biology. Light rainfalls are thus also considered in this work. The chapter is organized as follows. One first reviews the main physical, chemical and biological properties of dew and light rain. One then considers passive harvesting, using special condenser and collector shapes and materials, including new micropatterned surfaces. The problems of materials aging and the practical solutions used so far are also reviewed.

roughly 7 and 14 µm displays a marked deficit with the black body radiance at the same temperature. This is the so-called “atmospheric window”, characterized by the absence of water contribution in the atmosphere’s spectral radiance. Only present is a peak due to the stratospheric O3, whose influence is relatively weak due to the low temperature of the stratosphere. The emissivity of the sky, εs is thus lower than unity. Its value depends on the water content of the atmosphere, which can be measured, e.g. by its dew point temperature Td. The sky emissivity also depends on the atmosphere thickness, thus on the elevation of the place where it is evaluated. A useful formulation (Berger et al. 1992) is given by  εs = 1 − 0.2422 1 + 0.204323H − 0.0238893H 2  −(18.0132 − 1.04963H + 0.21891H) × 10−3 Td (◦ C) (3)

2 Dew Characteristics 2.1 Radiative Balance A black body (a substance that absorbs and emits all radiations) emits radiation at temperature Tc. Its spectral radiance per unit of scattering solid angle, B, follows the Planck’s law (Planck 1914). Once integrated over all wavelengths  and solid angle  = 2π above the black body surface, its radiative power Pr is expressed by the StefanBoltzmann law:

Pr =

ˆ∞

ˆ

d

0

d�B cosθ = σ Tc4

(1)

1 sph. 2

Here θ is the zenithal angle and σ = 5.67 10–8 W m−2 K−4 is the so-called Stefan–Boltzmann constant. A condensing surface usually exhibits discrete spectral bands of absorption and emission and is not a black body. It is a “grey” body. Its spectral radiance BG can be related to the black body’s spectral radiance by a spectral emissivity ε such as ε = BG /B. A total emissivity is then obtained after integration of all wavelengths. With Pε the grey body radiative power:

ε=

´∞ 0

d

´

1 sph. 2

d�BG cosθ

σ Tc4

=

Pε σ Tc4

(2)

A given surface exposed to a clear nocturnal sky (no clouds, no sun radiation) at a temperature around 300 K will emit infra-red radiation centered on  ∼ 10 µm. The surface absorbs the radiation emitted by the atmosphere molecules (mainly H2O and CO2) at about the same temperature. The atmosphere spectral radiance between

Here H (km) is the site elevation. From the definition of the emissivity (Eq. 2), one can define a sky temperature Ts as if the sky were a black body. With Ta (K) the atmosphere temperature, the power radiated by the sky Ps = σ Ts4 = εs σ Ta4 , giving Ts = εs1/4 Ta. For typical values Ta = 288 K (15 °C), relative humidity RH = 80% giving Td = 11.8 °C and at sea level H = 0, one obtains εs = 0.809 and Ts = 259.22 K (−13.9 °C). When clouds are present, they can be considered as black bodies with emissivity unity. One should notice that Eq. (3) corresponds to the sky emissivity integrated over all solid angles. However, the sky emissivity is dependent on the zenithal angle θ, minimum for θ ≈ 0°–20° (value ≈ 0.6), where the atmosphere layer is seen at its minimum, and maximum (value ≈ 1) for θ ≈ 75°–90°, where the apparent atmosphere layer thickness is maximum. Berger and Bathiebo (2003) related the angular emissivity εsθ with the total sky emissivity εs through the following relation: 1

εsθ = 1 − (1 − εs ) bcosθ

(4)

Ri = −ε c σ Tc4 + εc εs σ Ta4 ≈ −εc (1 − εs )σ Ta4

(5)

Here b is a numerical constant coming from the integration of the different atmospheric layers’ emissivities. The value b = 1.66 is from Elsasser (1942) and b = 1.8 from Bliss (1961). In general the balance of energy at the condensing surface will thus give a deficit. With εc the condensing surface emissivity, the balance of the emitted and absorbed radiations corresponds to a cooling power Ri = Pr − εc Ps, which can be written from Eq. (2) as:

The approximation where Tc ≈ Ta is justified by the small difference between air and condenser temperature when dew forms, due to a radiative deficit which remains less than 100 W m−2.

Emerging Water Recovery Processes from Dew and Light Rain

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2.2 Dew Volume Evaluation The balance of energy in the steady state of condensation can be estimated as (see e.g. Beysens 2018):

Ri Sc + Rhe + Rcond = 0

(6)

Rhe = aSc (Ta − Tc )

(7)

Here Sc is the surface area, Rcond corresponds to the release of latent heat by condensation and Rhe relates to the heat exchange by conduction with the materials below the surface and convection with the surrounding air. Generally, the condensing surfaces are isolated from below, and one can only consider the heat exchange by convection. With a as the heat transfer coefficient,

With t as time, m the condensed water mass and L the latent heat of evaporation, the condensation process corresponds to the flux.

Rcond = L

dm dt

(8)

The condensed mass is itself a function of the water vapor pressure difference pv (Ta ) − ps (Tc ), with pv (Ta ) the water vapor pressure at ambient air temperature and ps (Tc ) the saturation pressure at condensing surface Tc. By definition pv (Ta ) = ps (Td ), with Td the air dew point temperature. The parameter aw is the mass transfer coefficient of water molecules in air.    dm aw Sc pv (Ta ) − ps (Tc ) if positive = (9) 0 if negative dt

One assumes an infinite reservoir, so pv (Ta ) does not change in time. The case dm/dt < 0 corresponds to evaporation and is set to zero since here one only considers condensation. Equations (6) and (9) are coupled. However, the condenser temperature is always close to the dew point temperature due to the relatively low value of the available cooling power ( 0 and evaporation to h˙ < 0, which have to be discarded. The available radiative energy corresponds to RE. The convective heat losses between air and condenser are represented by HL. It is assumed for simplicity that a is a constant (= 3.5 W m−2 K−1, see Sect. 2.3) when windspeed V, measured at 10 m off the ground, is lower than V0 = 4.4 m s−1 and that condensation vanishes when V > V0. It thus becomes, with h˙ in mm per t:   �t(h.)  [0.06(Td − Ta ) + RE] if V < V0 12 h˙ = 0 if V > V0 (12) The available radiative energy RE depends on the air water content, as measured by the dew point temperature, the site elevation H (in km) and cloud cover N (in oktas). Note that when N = 9 according to the Synoptic Code SYNOP, then RE = 0. Using Eq. (3) for the sky emissivity:  RE = 0.37 1 + 0.204323H − 0.0238893H 2 − (18.0132 − 1.04963H       Td (◦ C) + 273.15 4 N +0.21891H 2 ×10−3 Td (◦ C) 1− 285 8

(13)

2.3 Wind Influence The velocity boundary layer and the thermal and mass transfer boundary layers, whose values are all close together (see e.g. Beysens 2022), are affected by the air velocity around the condensing surface. The heat exchange coefficient of the condensing surface with air can be written as a = a /ζ, where a is the air thermal conductivity and ζ the thermal (and hydrodynamic) boundary layer thickness. This thickness is defined by making the Peclet √ number Pe = 1. In a laminar regime, a should increase as V (Pedro and Gillespie 1982). For a planar surface, 1 m in length, inclined at 30° from horizontal, the 2D numerical simula√ tion by Flores-Castillo (2022) shows that a ≈ 3.11 V (V is the air velocity far from the boundary layer in m s−1, a is in W m−2 K−1). The heat transfer increases with windspeed, however air is often turbulent and the effect of windspeed is less pronounced than given by the above expressions, justifying the use of a constant heat transfer in Eq. (12). In Eq. (12), a = 3.5 W  m−2 K−1; it corresponds to the heat transfer under a laminar flow with velocity V ~ 1.3 m s−1. In other words, V = 1.3 m s−1 is the equivalent velocity of a laminar flow with a = 3.5 W  m−2 K−1.

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2.4 Nucleation

∆T

(15)

The prefactor Av for homogeneous nucleation (same Eq. 14 with f (θ) =1; units for N and Av: m−3 s−1) can be evaluated (Kashchiev 2000) from Av = c0 Zf ∗, where c0 is the volume concentration of the available nucleation sites. In humid air, all molecules can receive a cluster. Making use of the ideal gas equation, with pm the atmospheric pressure, c0 = pm /kB T . Z is the Zeldovich factor, related to the curvature of the free energy. The parameter f ∗ is the attachment frequency of monomers with the critical nucleus cluster. It depends on the saturation of condensing molecules in their environment. According to Kashchiev (2000), 1/3 αm D(SR)xs n∗1/3 where D is the mutual f ∗ = 48π 2 vm diffusion coefficient of vapor molecules in air, αm ≤ 1 is the monomer sticking coefficient, n∗ is the number of molecules in a critical cluster and xs is the water molecule concentration in air at saturation, in units of molecules per unit volume. From the ideal gas equation xs = ps /kB T . Using SR −1 typical values one finds Z ≈ 0.07, f ∗ ≈ 2 × 1011 lnSR s , 38 SR c0 ≈ 2.5 × 1025 m−3, and Av ≈ 3.4 × 10 lnSRm−3 s−1 W ∗ /kB T ≈ 88/(lnSR)2. The prefactor Ah for heterogeneous nucleation can be deduced from Av by rescaling c0 in surface concentration of available nucleation sites. From Christian (1975), the factor is the ratio of molecular volume vm and molecular surface

10

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10

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10

18

10

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10

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10

12

10

10

10

8

10

6

10

4

20

22

40

10 38 10 36 10 34 10

45° 0°

70°

32

90°

hom. 120° 180°

1

1.5

2

2.5

SR

3

3.5

4

10 30 10 28 10 26 10 24 10 22 10 20 10 18 10 16 10 14 10 12 10 10 10 8 10 6 10

-1

1 f (θ) = (2 + cosθ)(1 − cosθ)2 4

26

17.5

-3

2

10

14.5

(m .s )

3

16πσLV vm f (θ) − dN 3 (14) = Ah e (kB T ) [ln(SR)]2 dt The prefactor Ah for heterogeneous nucleation (units: m−2 s−1) exhibits a weak dependence on SR and θ. Here vm is the molecular volume of water, kB is the Boltzmann constant, T is temperature and σLV the liquid–vapor surface tension. The function f (θ ) is written as:

28

11

hom

2.4.1 Nucleation on Solids In the standard theory of heterogeneous nucleation on a solid surface, the nucleation rate is determined by the humid air supersaturation SR = pv (Ta )/ps (Tc ) and the wetting properties of water on the condensing surface are characterized by the drop contact angle θ. The nucleation rate dN/dt (N is the number of nucleated droplets per unit surface area) can be expressed as an exponential function of SR:

10

6.4

(dN/dt)

The main aspects of nucleation are summarized further. A full description of this process is out of the scope of the present chapter and can be found in, e.g. Christian (1975) and Kashchiev (2000) for nucleation on solids and Anand et al. (2015) for nucleation on liquids.

(dN/dt)het (m-2.s-1)

0

4.5

Fig. 1  Nucleation rate with respect to supersaturation SR = p/ps (lower abscissa) or (upper abscissa) temperature difference ΔT (semi-log plot). Different drop contact angles are shown in the heterogeneous nucleation case (left ordinate, in m−2 s−1). Homogeneous nucleation is shown by the red interrupted line vol. (right ordinate, in m−3 s−1). The value dN/dt = N˙ 0 = 106 m−3 s−1 (1 cm−3 s−1) is here considered as an actual experimental threshold in Eq. (16) for homogeneous nucleation and N˙ 0 = 104 m−2 s−1 (1 cm−2 s−1) for heterogeneous nucleation

4π(3vm /4π )2/3. With vm= 3×10–29 m3 the water molecular volume, the ratio Ah /Av ≈ 6.6×10–11m. Figure 1 shows the nucleation rates with respect to supersaturation SR for both homogeneous and heterogeneous cases, the latter concerning various contact angles. Scales and units are different for both processes. If one considers dN/dt = N˙ 0 as an experimental threshold to observe nucleation and if one neglects the weak SR/lnSR dependence with respect to the strong exponential variation, one can deduce from Eq. (14) a critical supersaturation ratio SR0∗ such that: � �1/2  3 2 v 16πσ LV m  � � f (θ) SR0∗ = exp (kB T )3 ln A/N˙ 0 (16)

The value N˙ 0 ~ 1 cm−3 s−1 is currently considered as a classical threshold to observe homogeneous nucleation, a criteria which can be extended to heterogeneous nucleation with N˙ 0 ~ 1 cm−2 s−1. Both N˙ 0 and A precise values are not needed since they enter in Eq. (16) as a log. In Fig. 1 the case where the drop contact angle θ = 180° cannot be compared with the homogeneous nucleation case because of the different units. A threshold supersaturation SRc ≈ 3 is needed to nucleate droplets. In an air saturated at 20 °C, temperature must be lowered to ≈1.5 °C for homogeneous nucleation to start. In contrast, when the contact angle is 70°, nucleation starts to

Emerging Water Recovery Processes from Dew and Light Rain

occur at ≈11 °C. For the complete wetting case where water forms a film (θ = 0°), nucleation occurs for SRc = 1, that is at the dew point temperature (= 20 °C). However, in practice, the geometrical and/or chemical defects of the surface act as preferred nucleation sites and heterogeneous nucleation can be seen at lower supersaturation.

2.4.2 Nucleation on Liquids Because some substrates are infused with oil (liquid-infused substrates, see e.g. Anand et al. 2012, 2015; Smith et al. 2013), it is interesting to consider nucleation on a liquid immiscible with water (oil). When oil wets imperfectly water, nucleation proceeds as on solids, with however some complications arising from the different contact angles of water/oil, water/air, oil/air (Anand et al. 2015). However, the case where oil spreads on water leads to a different process. Nucleation of a water drop at the surface of oil leads to a fast cloaking of the droplet by oil, followed by the submergence of the droplet within the oil. A fresh oil–air interface is thereby created where nucleation can again occur, forming a cycle of nucleation—submergence and the formation of a large number of submerged droplets. Such nucleation-driven condensation can increase water yield with respect to the classsical diffusion-limited condensation process (see Sect. 6.2.4/Liquid-Imbibed Substrate and Fig. 8).

2.5 Droplet Growth 2.5.1 Solid Substrate Once nucleated, droplets grow on a solid or liquid substrate (case without oil cloaking) by incorporating the water molecules that hit their surface. Water molecules are in Brownian motion and the probability to be incorporated is larger near the droplet surface. It thus results in a concentration profile of water molecules. Droplet growth is ensured by the diffusion of water molecules. Diffusion is indeed more efficient than convection in a diffuse boundary layer of extent ζ defined by the Peclet number Pe = Uζ /D < 1 . Here U is the air flow velocity parallel to the surface far from it and D is the diffusion coefficient of water molecules in air. The extent of the boundary layer is typically ζ ~ mm (Medici et al. 2014; for more details, see Beysens 2022). One classically distinguishes several states of growth (see Beysens 2018, 2022 and Refs. therein). (i) The mean distance between nearest neighbors nuclea√ tion sites is �d0 � ∼ 1/ 4ns , assuming complete spatial randomness without finite size effects (Clark and Evans 1954). ns is the surface density of nucleation sites. (ii) The droplets grow with low surface coverage. They thus undergo no or a few coalescence events. The drop

5

contact radius R exhibits a power law variation with time t as R ∼ t α. The value of the exponent α depends on the distance d0  between droplet centers as compared with the diffusive boundary layer ζ. . When far apart from each other (d0  > 2ζ) the drops evolve independently with a hemispherical concentration profile of water molecules centered on each drop, resulting in α = 1/2. For a hemispherical drop of contact radius R, one obtains: 1

R = (As t) 2

with:

As = 2

 D  pa (Ta ) − ps (Tc ) rv ρ w T

(17)

(18)

Here pa (Ta ) is the water vapor pressure at or further from the diffuse boundary layer and ps (Tc ) is the vapor pressure saturation at drop surface temperature. The latter temperature is assumed equal to the condensing surface temperature (for more details, see Beysens 2022 and Refs. therein). rv = 462 J kg−1 K−1 is the water specific mass constant. The general case of a non-hemispherical spherical cap, characterized by the contact angle θ, leads to the same formulation as above with a θ-dependent prefactor (see Beysens 2022). If the drops are closer to each other (�d0 � ≪ 2ζ ), the individual concentration profiles overlap. It results in an average linear profile, perpendicularly to the substrate. The growth exponent is smaller, α = 1/3, because the drops have to compete to absorb moisture. Considering an equivalent film of thickness h on condensing surface with area Sc having same volume than the sum of drops volumes Vi, its valuecan be expressed as  3 h = (1/Sc ) Vi = π(G(θ)/S  c) Ri3. The function 3 G(θ) = 2 − 3cosθ + cosθ / 3sinθ relates the volume Vi of a drop spherical cap to its contact radius Ri through Vi = πRi3 G(θ ). The film grows linearly with time in the steady state of condensation such as

h=

 D  pa (Ta ) − ps (Tc ) t rv ρ w T ζ

(19)

or, going back to the individual drop radius,

Ri = (Ai t)1/3

(20)

one gets, with h = Vi /Si,

Ai =

  4D pa (Ta ) − ps (Tc ) �d0 �2 πG(θc )rv ρ w T ζ

(21)

The quantity 4d0 2 is the surface of influence of a drop i where water molecules can be collected. It corresponds to the mean distance d0  between nucleation sites in stage (i) with Si = 1/ns ∼ 4�d0 �2.

6

D. Beysens and M. Muselli

(iii) Then droplets touch each other and coalesce, leading  to a constant surface coverage ε2 = π Ri2 /Sc and a self-similar growth behavior. The concentration profiles around drops still overlap, leading as before in (ii) to a mean concentration profile directed perpendicularly to the substrate, corresponding again to the exponent α = 1/3 for each individual drop. The average (Sauter) radius of the droplet pattern can be related to the total condensed volume VT and surface coverage ε2 as �R� ∼ �R3 �/�R2 � = VT /ε2 Sc G(θ) = h/ε2 G(θ) where one has made apparent the equivalent film thickness h. Since the latter grows linearly with time, it follows

�R� =

h = kP t ε2 G(θ)

(22)

From Eq. (19), the growth rate kP is thus:

kP =

 D  1 pa (Ta ) − ps (Tc ) ε2 G(θ) rv ρ w T ζ

(23 )

One notes that the mean radius is proportional to the condensed volume �R� ∼ VT . (iv) Because of the self-similarity of the growth, the mean distance between drops, d, increases proportionally √ with R, �d� = �R� π/ε2 . When d > 2ζ, the concentration profiles do not overlap anymore and nucleation of new droplets can occur between neighboring drops. The new nucleated droplets then exhibit the same growth laws as described above. (v) Gravity effects arise during the late stages (iii)–(iv), resulting in the deformation of the drop shape on a horizontal substrate and/or sliding on an inclined substrate. Shedding controls the maximum size of the drops remaining on the surface, R0. The size distribution of droplets in this stage follows a power law n(R) = (1/3π R03 )(R/R0 )−8/3 (see e.g. Beysens 2022). A special Sect. 6.2 is devoted below to water collection by gravity (Fig. 2).

2.5.2 Liquid-Infused Substrate A particular type of surface (micropatterned, polymers) can be wet and retain liquids on its surface (Anand et al. 2012, 2015; Smith et al. 2013). Using non-miscible liquids with water (oil), their surface is like a liquid film. When oil does not wet water, the growth laws on the liquid are similar to the laws on solids of Sect. 2.5.1. However, when oil wets water, a different type of growth proceeds. As discussed in Sect. 2.4.2, nucleation of a water droplet leads to near immediate cloaking of the droplet by oil, followed by its submergence in the oil film. Submergence leaves a fresh oil-air interface where nucleation can again occur, forming a cycle nucleation–submergence. It follows the

Fig. 2  Drop pattern showing self-similar growth when condensing on a hydrophobic glass surface. The picture largest dimension in a–c corresponds to 285 µm and 1.1 mm in d. a Stage (i): Nucleation of isolated droplets on the substrate defects and growth without coalescences corresponding to stage (ii). b Stage (iii) at time t = 1  s after the beginning of condensation, exhibiting a dense pattern of droplets undergoing coalescences. c Same stage (iii) as in b but later at t = 6  s. In accord with growth self-similarity, the pattern is statistically equivalent to the b pattern after rescaling by the mean drop radius. d Stage (iv) at t = 25 s with a new scale ×0.25. Between the initial drops new families of droplets have nucleated. When considered independently, these families exhibit the same self-similar characteristics of the first drop pattern in b, c (From Beysens 2022, with permission of Springer)

formation of many submerged droplets, which grow only by coalescence. It is worth noticing that this condensation process is not limited by a concentration gradient as discussed in Sect. 2.5.1. but by the nucleation process itself. It appears (Lavielle 2022) that condensation with engulfment can be much more efficient than the process limited by diffusion (see Sect. 6.2.4.3).

3 Light Rain Characteristics Collection of rain water by surfaces is very classical. When rain is weak, droplets are pinned like dew droplets. The rain and light rain characteristics are reviewed as follows.

3.1 Main Rain Characteristics Liquid rain droplets and ice crystals nucleate on atmospheric aerosols whose typical size is ~0.2 µm (Kashchiev 2000) and further grow by diffusion of water molecules, in a way similar to dew nucleation. The growth law is limited by the water vapor  diffusiongradient and thus the drop or ice radius R ∼ pa − ps (R) t 1/2. In the so-called warm rain process, where water is liquid (supercooled below 0 °C), droplets (typical size 20 µm) collide in the cloud due to air turbulence and coalesce, leading to larger drops

Emerging Water Recovery Processes from Dew and Light Rain

that eventually fall as rain (typical size 0.1–1 mm). During their descent, droplets still collide and coalesce but also, due to the air resistance, deform and fragment. This process results in an exponential distribution of the drop diameter d, n(d) = n0 exp(−d/�d�). Here n0 is a constant (= 0.08 cm−4) measuring the average spatial density at the ground level and d (cm) is an average diameter related to the rate of rainfall R (mm h−1) by �d�−1 = 41R−0.21 (Villermaux and Bossa 2009). Here n(d) is the number of droplets per unit volume that have diameters between d and d + dd. If air is below 0 °C, water is most often a supercooled liquid. The drops can freeze nearly instantaneously by contact with a foreign substance acting as a heterogeneous nucleation site (Bergeron 1935). The resulting ice crystals do not coalesce and have to grow enough to fall down. Because the temperature generally increases when height decreases, the ice crystals may melt and become rain as they fall.

3.2 Light Rain Deposition and Collection Light precipitations correspond to hourly rainfall of 0.1– 0.3 mm (Yang et al. 2021). Light rain represents a meteorological phenomenon reported with a larger frequency than rainstorms. In China, Chen et al. (2010) demonstrated than light rain was observed with an annual frequency of 75%. Drops in light rain, drizzle, exhibit size in order of 0.2–0.5 mm, smaller than rain drops (size ~1 mm) (AMS Glossary of Meteorology 2022). When such drops hit a surface, they become pinned like the dew drops. Drop coalescence occurs in two steps. One falling drop hits a surface drop, which grows and is able to touch a neighboring drop and coalesce with it. A family of larger drops emerges, fed by the flux of falling drops, whose evolution is similar to dew (Sect. 2.5.1). In a sense, the falling droplets play the role of the water molecules which are incorporated by diffusion in dew drops during their growth.

4 Dew and Rain Chemical Properties The chemical properties of dew are due to the absorption of gases at the dew formation site (CO2, SO2, NO, NO2, a fast process), the solubilization of aerosols (NaCl, MgCl2, CaCO3 …) deposited on the condensing substrate and the chemical reactions that take place in the dew drop. Concerning rain, whose water flux is more important than dew’s, the role of deposited aerosols becomes negligible. The chemical properties will be rather connected to the nucleation seed, the adsorption of gases in the cloud and the aerosols scavenged during the cloud transit and in the

7

course of the descent to the ground. Chemical reactions in the drops are also an important aspect. Light rain and drizzle have in principle chemical characteristics intermediating between rain and dew. However, their properties are in general properties closer to dew because the concentration of deposited aerosols on the collecting surface with whom they interact is in general larger than scavenged by a small rain drop during its transportation in clouds. Over the last decades, various studies have determined the chemical composition of dew and rain in a few locations. Further, a review of the physico-chemical properties of dew and rain samples collected at the same place and in the same time period concerning the major and minor ions is presented. The following determinations were summarized: (i) Physico-chemical properties: electrical conductivity EC and pH; (ii) chemical concentrations for cations (major, Na+, K+, Ca2+, Mg2+, NH4+, H+ and minor, Fe2+, − 2− Zn2+, Cu2+, Al3+) and anions (major, Cl−, NO− 3 , NO2 , SO4 3− − − − and minor, PO4 , HCO3 , CH3COO , HCOO ). The ion concentrations are also compared with the WHO-specific guidelines for potable water (WHO 2017, 2022). One will see that the concentration of ions is quite generally smaller in rain than in dew. This is a mere dilution effect, the collected rain volume being in general larger. Toxic substances present in the atmosphere can be dissolved in dew and rain, such as per- and polyfluoroalkyl substances (Cousins et al. 2022) or polycyclic aromatic hydrocarbons and alkanes (Ambade et al. 2020). The present review does not account for the presence of these substances, which need more refined chemical analysis than the regular analyses carried out for water quality.

4.1 pH and EC Measurements According to Tables 1, 2, 3 and 4, the rain pH appears more acidic than dew samples with respec1.05 (mean on 29 sites) and tively  = 5.56 ±   = 6.22 ± 1.02 (mean on 17 sites). The pH values show large disparities according to the sites, with values between 4 (Allegheny, USA) and 7.9 (Ajaccio, France) for dew and 4.1 (Warren, USA) and 7.3 for rain (Negev Nizzana, Israel). The standard deviations do not exceed 1 pH unity. The two median values (50% of the global samples) are 6.6 for dew against 5.6 for rain, corresponding indeed to having rain more acidic than dew with 1 pH unity difference. This result has been already observed in Bordeaux (Beysens et al. 2006). Acidity in water is linked to the presence of sulfur dioxide (SO2) and nitrogen oxides (NOx) in the atmosphere, mainly of anthropic origin (road traffic and industries). According to rural or urban conditions, dew can be more or less acidic due to the absorption

6.7

6.3

7.9

6.5

–

–

6.8

6.8

4.7

7.2

6.9

Bordeauxf

Ajacciog

Parish

Tahitii

Tikehaui

Rampurj

Delhik

Panandhrol

Sayaram

Sutharim

Sataparm

France

7.3

7.4

5.5

Jubaihaq

Mirleftr, ad

Wroclaws, t

Jordan

Jordan

Morocco

Poland

5.2

4.4

Krakowv

Gaik– Brzezowaw

5.3

6.7

Ammanp

Japan

Szrenica

–

5.2

Yokohamao

Mt.u

533

32

62

18

54

725

613

129

230

6.9

Negev Desertn 7.4

930

520

230

271

–

340

238

124

114

29

195

308

–

155

230

226

340

114

2500

92

174

68

145

2409

2940

639

246

2751

–

–

834

413

730

350

619

709

73

1710

62

392

690

403

605

714

109

EC Ca2+ (µS cm−1) (µEq L−1)

Israel

India

French Polynesia

6.7

Zadare

Croatia

Bangladesh Costal Bholab

China

6.6

6.8

Median

6.4

1.6

IQR

Changchund

6.8

Q3

Santiagoc

5.3

Chile

9.5

pH

Q1

City

max WHOa

Country

21

56

31

27

1332

324

230

56

402

–

–

63

290

200

140

57.6

239

30

230

800

45

205

60

202

232

31

Mg2+ (µEq L−1)

Table 1  Chemical analysis of dew in the literature (major ions)

38

43

25

34

4318

652

157

128

954

–

–

107

192

1850

1060

256

422

157

310

112

75

235

143

299

338

40

8700

Na+ (µEq L−1)

13

19

10

35

243

68

31

25

135

–

–

69

113

103

42

43.5

61

10.5

59

62

63

136

44

53

69

16

K+ (µEq L−1)

42

31

32

93

–

–

44

445

102

–

–

–

255

–

–

6

14

–

50

–

384

–

58

87

119

33

NH+ 4 (µEq L−1)

–

–

5

36

–

–

–

–

–

–

–

–

–

–

–

0.33

–

1.4

2.6

–

–

–

5

17

18

1

H+ (µEq L−1)

21

37

31

53

7207

455

138

170

1148

903

4541

1608

1608

190

348

2050

1300

251

465

156

650

100

133

290

180

779

840

61

7000

Cl− (µEq L−1)

134

167

84

114

240

81

45

90

785

–

–

131

121

10

40

190

68

45

11

170

110

223

90

113

158

45

800

NO− 3 (µEq L−1)

–

–

–

14

–

–

–

73

–

–

–

–

–

 NH4  > Mg  > K (H not detected). The Na+ and Mg++ ions were found significantly higher in only a few sites close to the sea (Tikehau, French Polynesia; Mirleft, Morocco; Ajaccio, France) and are clearly of sea origin. The high presence of Ca++ in many samples observed on several locations (dew: 2940 μEq L−1 in Jubaiha; 2409 μEq L−1 in Mirleft (Morocco) and 1710 μEq L−1 in Zadar (Croatia); rain: 1015 and 1215 μEq L−1 in the Negev desert) can be explained by the filtration of calcium by the soil or by an aerosol of coral origin. When ammonium is found in water, it commonly reveals an incomplete degradation process of organic matter. Its presence is then an excellent indicator of water pollution by organic releases of agricultural, domestic or industrial origin. One notes the presence of NH+ 4 in fairly large proportion for rain samples in Beijing (China) with 363 μEq L−1 or Delhi (India) with 371 μEq L−1 or

D. Beysens and M. Muselli

dew samples at Yokohama (Japan) and Santiago (Chile) (445 and 384 μEq L−1, respectively) representing more than of 3 times the mean values.

4.2.2 Anions Similar to the major cations (Tables 1 and 3), dew and rain − − anions show a similar trend: Cl− ≫ SO2− 4  > NO3  > NO2 . . All species present large standard deviation around their mean value (as an example,  dew = 803 ± 1527 μEq L−1 (30 sites) and rain = 464 ± 995 μEq L−1 (16 sites). The high values of Cl− are mainly observed in coastal and marine sites. When the distance from the sea exceeds 100 km, Cl− concentrations become low (300

Ajaccio

2002–2003

136,190

254,660

Morocco

Mirleft

2007

340

170

French Polynesia Rain

Tahiti

2004

>300

>300

French Polynesia

Tahiti

2004

>300

>300

France

Bordeaux

2002

15

>300

6 Dew Water Condensation and Collection etc.) that remove most of the radiations emitted near the In the following are reviewed the main processes that can be optimized for increasing dew condensation and water collection. Two main processes have to be considered separately, condensation and water collection by gravity.

6.1 Enhanced Condensation 6.1.1 Radiation Deficit In order to increase the available cooling power Ri, Eq. (5) shows that one should (i) increase the condenser surface emissivity in the atmospheric window and (ii) decrease the atmosphere emissivity. Concerning surface emissivity in the atmospheric window, some specific materials have been elaborated as LDPE foil (Nilsson et al. 1994; Vargas et al. 1998) where the BaSO4 microparticles emit in the atmospheric window. However, one has to note that sooner (with high emissivity substrates) or later (with low emissivity substrates) the emissivity of condensed water (0.98 in the atmospheric window) will dominate the radiative process (Trosseille et al. 2022). One notes that the angular dependence of the substrate emissivity could be modified by specific surface treatment (roughness) and might better match with the angular dependence of the sky emissivity. The sky emissivity indeed depends on the zenithal angle (see Sect. 2.1). Then selecting, e.g. aluminum mirrors, a solid angle near the zenith (Howell 2021; Haechler et al. 2021) allows to considerably reduce the sky emissivity seen by the condenser and remove the near horizon obstacles that emit IR radiation (Awanou 1998; Berger and Bathiebo 2003; Clus et al. 2009; Howell et al. 2021; Haechler et al. 2021). In particular, angles that are below 15° with horizontal have to be avoided because there εs reaches unity (Eq. 4). Hollow structures (origami, ridge, hollow cone,

horizon are thus interesting designs (Awanou 1998; Clus et al. 2009; Beysens et al. 2013; Howell 2021; Haechler et al. 2021; see Table 6). Some materials (metamaterials) have been specially designed to emit in the far IR and reflect the sun light spectrum. The goal is to condense dew water during day time. One can cite the use of photonic solar reflector and thermal emitter consisting of multi layers of HfO2 and SiO2

Table 6   Characteristics of several types of dew harvesters. Convex structures are not usually used because of large wind influence (Adapted from Beysens 2018, with permission) Type

Positive edge effects

Symmetry w.r. air flow

Plane-horizontal

N

Y

Grid-horizontal (Hilner balance)

N

Y

Plane-tilted

Y

N

Origami

Y

Y

Ridges

Y

Y/N

Egg box

N

Y

Hollow cones: smooth bi-cone corrugated

Y

Y

YY

a

Hollow polygons: pyramids, etc.

Y

Y

Hollow with mirrorsa

Y

Y/N

Hollow spherical cup

Y

Y

Positive cone

Y

Y

Sphere

N

Y

Howell (2020)

16

that reflects 97% of incident sunlight while emitting selectively in the atmospheric window (Raman et al. 2014). Another metamaterial (Zhai et al. 2017) is constituted of SiO2 microspheres set randomly in a polymethylpentene matrix, transparent to the solar spectrum. The metamaterial is backed with a silver coating to reflect sunlight. It shows an infra-red emissivity >0.93 in the atmospheric window. It has economical roll-to-roll manufacturing. Haechler et al. (2021) used a selective emitter consisting of a radiative cooling coating (polydimethylsilane PDMS on an IR-emissive glass substrate, transparent to the visible light). The substrate’s backside is coated with a thin layer of silver to serve as a sunlight reflector. Although these new metamaterials exhibit a relatively high emissivity (~0.93) and a noon-time radiative cooling power around 90 W m−2, their wetting properties are not specific and drop collection is not optimized, leaving pinned the smallest dew drops. More important, it is most often impossible for any radiative materials to reach during the day the dew point temperature because the relative humidity is generally low during the day and thus cooling has to be made far below the air temperature. These materials would be, however, helpful to condense sooner in the evening and later in the morning. Although a little bit less efficient to reflect sunlight, other materials have been designed to also reflect most of the sun radiation while keeping a large IR emissivity and good drop collecting properties. It is the case of the LDPE foil with TiO2 and BaSO4 microparticles with insoluble surfactant (Nilsson et al. 1994; Vargas et al. 1998; manufactured by OPUR 2022) and the OPUR mineral additive (OPUR 2022) to be immersed in any paint adapted to the substrate materials and showing good sun reflectivity.

D. Beysens and M. Muselli

or using hollow forms such as ridges, inverted pyramids, polygons, cones or periodic structures such as egg box-like, origami (see Table 6).

6.2 Water Collection by Gravity In the following content one considers a planar surface of length L and oriented with an angle α with horizontal. The conditions of water collection at the bottom of the surface, at distance L from its upper edge, are discussed below.

6.2.1 Film Condensation and Collection As long as dew is concerned, cooling is ensured at the surface level by radiation deficit (see Sect. 2.1). This situation contrasts with the well-known Nusselt film (see e.g. Incropera and DeWitt 2002) corresponding to a contact cooling below the condensing surface. In that case, the variation of the Nusselt film thickness with L is: 

4ηw (Ta − Tc ) hL = ρw2 Lv gsinα

1/4

L 1/4 (25)

Hereη is the liquid water shear viscosity, w is the water thermal conductivity, ρw is water density, Lv is the latent heat of evaporation, g is the earth acceleration constant and α is the angle that the surface makes with horizontal. The above description of film drainage is in agreement with the observation (Lee et al. 2012; Fig. 3). When radiative cooling with power per surface area Ri is present, and the substrate materials is adiabatic (w = 0), the film thickness of the film at the lower end of the plane becomes (Beysens 2018, 2022):

6.1.2 Reduce Heat Losses Dew yield (Eq. 12) is limited by the heating effect of the substrate heat losses with the surrounding air, measured by the coefficient of heat transfer. From its definition in Eq. (7), this coefficient can be written as (Holman 2002):  dT  a = −a (Tc − Ta )−1 = a /ζ (24) dz s

Here z is the normal direction to the substrate, a is the thera mal conductivity of air and dT /dz|s = Tc −T the thermal ζ gradient at the surface location. One sees that a increases with the air flow velocity near the surface, when the hydroζ decreases. On a planar dynamic boundary layer thickness√ surface and laminar air flow, a ∼ V (Pedro and Gillespie 1982). In order to increase ζ, the air flow near the surface has to be made minimum. This can be done by orienting a tilted planar surface against the wind (Beysens et al. 2003)

Fig. 3  Linear puddle formed after 1800 s at the end of a square vertical hydrophilic surface of side L cooled by contact. Advancing/ receding contact angles are 4° and 0°, respectively. Surface area is L × L = 30  × 30 mm2. Condensation rate is 0.25 mm/h. The white bar is 10 mm (From Lee et al. 2012, with permission of ACS)

Emerging Water Recovery Processes from Dew and Light Rain



hL = −

�

3η Ri +

a ζ (Ta

− Tc )

ρw2 Lv gsinα

� 1/3 

L 1/3

17

(26)

Let us consider a typical situation as in Howell et al. (2018) where Ri ≈ −80 W m−2, Ta − Tc ≈ 2 K, α = 30° and L = 1  m. Using ζ ~ 5 mm, η = 1.5 × 10–3 Pa s, ρw = 103 kg m−3, Lv = 2.5  × 106 J kg−1 and a = 0.026 W m−1 K−1, one obtains hL ≈ 30 µm. With h˙ the condensation rate per surface area, the final collection time corresponds to the time t0 (=δz/3h˙ ) to form a film above the surface roughness δz, plus the time t1 (~0.75hL /h˙ ) (Beysens 2018, 2022) to condense the volume stored in the stationary film, plus the time tc to drip water accumulated at the lower surface edge. When a puddle is present, this time corresponds for the puddle to reach √ a section on the order of the capillary length lc = σ/gρw , that is tc = tcp ≈ 2lc2 /L h˙ . When a drip edge device is used, the cylindrical puddle concentrates in a unique drop, which detaches when its volume reaches vc ~ (4π/3)lc3 after time tc = tcd = vc /L 2 h˙ . The minimum time tf to collect water detaching from the plate end is thus:   1 1 sc vc tf = t 0 + t1 + tc = δz + 0.75hL + or 2 (27) L L h˙ 3 The values above and a typical dew condensation rate h˙ = 0.02 mm h−1 gives tf ≈ 4700 s (linear puddle) or lower than 2100 s (drip edge device).

6.2.2 Dropwise Condensation and Collection. Edge Effects A drop of volume Vd on an inclined substrate (angle α with horizontal) is submitted to two antagonist forces, the gravity force Fg = ρVd gsinα and the contact line pinning forces, Fs. The latter is non-zero because, in general, the advancing (θa) and receding (θr) contact angles are different. The resulting pinning force along the direction x of the substrate can be written, with σ the liquid gas surface tension, as Fs,x = k ∗ σ R(cosθr − cosθa ) (ElSherbini and Jacobi 2006). Here k* is a numerical constant that depends on the precise shape of the drop. For circular and ellipsoidal-like drop, k ∗ =1.548. During condensation, the drop grows and slides when its radius R reaches a critical value Rc such as Fg = F s, giving 1/2    cosθr − cosθa 1/2 k∗ Rc = lc (28) π G(θ) sinα

For a substrate tilt angle α = 30°, contact angles θr ≈ 40° and θa ≈ 70° (θ ≈ 55° and G(θc ) = 0.29), one finds R0 ≈

1.2lc ≈ 3.2 mm, that is a value slightly larger than the capillary length lc = 2.7 mm. The lag time tf for a condensing drop radius to reach Rc and slide down can be evaluated for the same condensation rate h˙ = 0.02 mm h−1 as above in Sect. 6.2.1 for filmwise condensation. Using the mean film approximation of ˙ f = G(θ )ε2 Rc, Sect. 2.5.1 and Eq. (19) one obtains h = ht where ε2 is the drop surface coverage. The latter varies with the contact angle as (Zhao and Beysens 1995):

ǫ2 = 1 −

θ (deg.) 180

(29)

The lag time becomes:

tf = Rc

G(θ )ε2 h˙

(30)

With the values used above (Rc = 3.2 mm, θ ≈ 55° giving ε2 ~ 0.7 from Eq. 29), one obtains tf ~ 1.1×105 s (32 h). This time is very large, however in practice it is smaller. Firstly (ElSherbini and Jacobi 2006), a correction has to be made on the measurements of contact angle hysteresis due to the influence of gravity as measured by the Bond number (Bo = 4R02 ρw gsinα/σ ). Then, the model giving Eq. (28) is static. In reality, a drop detachment always occurs owing to a coalescence event (Trosseille et al. 2019) because (i) coalescence makes the drop radius grow instantaneously, surpassing Rc, and (ii), during coalescence, the drop contact line moves, which lowers the pinning forces (Gao et al. 2018). Typical dropwise condensation experiments are shown in Fig. 4. The experiments are carried out on the same duralumin materials with the same condensation conditions. The only difference is the fact that in Fig. 4a, b the surface is smooth while it is sand blasted in Fig. 4c, thus increasing the density of nucleation sites. The dispersion in lag times observed on the smooth surface (but not on the sand blasted surface) is due to defects and pollution effects, which make the nucleation rate and pinning force vary.

6.2.3 Enhanced Drop Collection by Edge Effects One should note that near the edges, the diffusion water vapor profile is modified around the drops, allowing them to collect more vapor. There the drops grow faster (Medici et al. 2014) and detach sooner, acting as natural wipers, coalescing and collecting many drops on the surface in an avalanche effect. Dew yield with edged surfaces, e.g. with Origami shapes, therefore gives more collected water than surfaces with a few edges, especially when the dew yield is small, corresponding to tiny drops (Fig. 5).

18

D. Beysens and M. Muselli 0.10

0.20

0.16

0.08

0.12

0.06

0.08

tf

tf

0.04

0.02

0.04

0

c

b

h (mm)

h (mm)

a

0 0

0.5

1

1.5

t (hour) Fig. 4  Condensation on a smooth squared surface of Duralumin placed vertically and cooled by conduction. Roughness is δz = 0.4 µm, advancing/receding angles are 98°/28°, side dimension is 14.7 cm, thickness is 3 cm, condensation rate is 0.17 mm h−1, giving tf ~ 0.7 h after correcting with the Bond number (Trosseille et al. 2019). a Picture where a few droplets on the smooth surface, much larger than the average, are at the sliding onset. White bar: 10 mm. b Collected mass with lag time tf. The interrupted line is condensation on the plate. The lag times dispersion is due to the presence of

0

0.5

t (hour)

unavoidable geometrical and chemical defects from chemical pollution. The surface roughness is δz = 0.5 µm. c Surfaces of Duralumin once sand blasted with 25 µm silica beads (roughness δz = 2 µm, advancing/receding angles 95°/20°) cooled by conduction. The edge effects have been annulled by using absorbers. One notes a strong reduction in the dispersion of lag times with respect to the smooth materials in b (Adapted from Trosseille et al. 2019, with permission of Springer Nature)

b a

Fig. 5  a Origami, egg box and reference plane condensers. b Ratio (%) of the condensers and reference plane yields as a function of the reference plane yield (Origami: OR, red squares, red line; egg box: EB, full blue circles, blue line; reference: REF, black interrupted line). The thick lines are smoothing of the data (Data from Beysens et al. 2013)

6.2.4 Enhanced Drop Collection by Surface Treatment Heat transfer by condensation is an important topic for industry. Dropwise condensation is known to increase the condensation rate with respect to filmwise condensation and consequently the heat transfer. The basic reason lies in the fact that drops slide before reaching a large radius, in contrast to films, which permanently exhibit a large thermal resistance. The smaller the sliding drops, the smaller the thermal resistance and the better the yield. A very large number of studies have been thus carried out to sooner collect drops by gravity (see e.g.

Beysens 2022; Liu et al. 2022). However, aging of the surface treatment is the main problem that prevented till now the use of dropwise condensation in industrial heat exchangers although more than 14,000 papers have been published on the topic so far (Erbil 2020). Note that in the case of dew collection, filmwise condensation, being driven by surface radiative cooling, does not lead to the same thermal limitation as with contact cooling. In the following content one focuses on surface treatments and micropatternings that can be easily scaled on large surfaces. One also considers substrates that can keep their performance under outdoor conditions.

Emerging Water Recovery Processes from Dew and Light Rain

19

BS+PTFE

tf

Fig. 6  Time-dependence of the volume per unit area h of the collected sliding droplets. S, full black squares: Plain silicon. Red dots: BS + PTFE (Black Silicon PTFE-coated, see the inset). The steps in the S-curve correspond to sliding events, starting at time tf. On the BS + PTFE surface the sliding droplets experience a zero offset tf. ≈ 0 (immediate departure) (From Liu et al. 2021; open access)

Filmwise Condensation Forming a film by condensation needs to use superhydrophilic surfaces. This is an interesting situation because nucleation occurs as soon as the dew point temperature is reached (see Sect. 2.4). The flow is limited by the time to overwhelm the roughness of the surface, reach the stationary thickness and detach the puddle at the end of the plate (Sect. 6.2.1, Eq. 27). The last time becomes negligible if a special drip is used. It is however difficult to make a surface hydrophilic enough to form a continuous film on a smooth surface. Plasma functionalization can be used (see e.g. Pocius 2021). It reduces the contact angle but zero contact angle is hardly met on smooth surfaces. Superhydrophilic surfaces allow a water film to be formed. These surfaces are micropatterned and their roughness increases their hydrophilic character. Defining θ the contact angle on the smooth surface and θw the contact angle on the rough surface whose roughness is r (ratio: drop actual surface contact/drop projected area), one obtains (see e.g. Milne and Amirfazli 2012).

cosθw = rcosθ

(31)

An example of such materials is black silicon, with needlelike structures (Her et al. 1998; Nguyen et al. 2013). Combined structures consisting of thin superimposed biphilic surfaces were also studied by Oh et al. (2018). A thin hydrophilic porous matrix of nickel inverseopal nanostructures is covered with hydrophobic polyimide, on which dropwise condensation can occur. One thus obtains a superhydrophilic sublayer with a

superhydrophobic top layer. On this top layer drops nucleate and grow before being sucked in the sublayer, where flow can take place. Surfactant insoluble with water (and food proof, that is non-toxic to humans for use with food) can be inserted at the surface of LDPE films, containing microparticles of TiO2 and BaSO4 to increase their emissivity (Vargas et al. 1998; Nilsson et al. 1994 manufactured by OPUR 2022). This material is currently used outdoors. However, outdoor conditions can increase the roughness and remove the surfactant top layer on a time scale of order months. A particularly simple micropatterned surface is made of hydrophilic microgrooves (Bintein et al. 2019). Grooves are aligned along the direction of gravity. As soon as condensation starts, a film forms in the grooves, filling them with capillarity effects and allowing water to flow downwards. The above modified LDPE films grooved by hot pressing show that the collecting properties are maintained under outdoor conditions (Lavielle et al. 2022). However, if one excepts the above grooving, most if not all the above treatments and/or micropatternings do not last long under repeated cycles of condensation and evaporation and under harsh outdoor conditions (Erbil 2020). Other treatments, which last longer, are concerned with mineral particles (aluminosilicates, TiO2) which are mixed with paint or varnish to both increase emissivity and make the surface hydrophilic. Hydrophilicity is due to a photo reaction with sun UV (Wang et al. 1997). These coatings are very resistant to outdoor conditions as we personally observed during 10 years of continuous functioning in Bordeaux (France) and Paris (France). Fibrocement is a cheap material, commonly used for roofs. Made of cement, organic fibers and mineral additives, its superficial structure is highly porous, with roughness δz ~ 0.1 mm. The condensation process begins by filling the pores of the surface, and then an irregular film forms and water starts to flow. Water starts to be collected after time of the order of t0 ∼ δz/h˙ , corresponding to a trapped water layer of δz thickness (Beysens 2018, 2022). Dropwise Condensation This is the most general mode for dew condensation because of the outdoor unavoidable contamination by fat substances and the effect of abrasion by dust. On smooth surfaces, aging eventually leads to critical drop sliding radii on the order of mm, leading to typical onset times on the order of hours for typical condensation rates on order of a few mm h−1 (see Fig. 4). On superhydrophobic surfaces, the coalescence of two micro-droplets can deliver enough energy to induce jumps out of the surface, improving water collection. Mouterde et al. (2017) and Liu et al. (2021) used micro-cones in place of cylindrical pillars, improving the jump efficiency.

20

D. Beysens and M. Muselli

a

grooves

smooth

b

0.3 65µm

0.25

150µm

500µm

(dh/dt)

c

m (g)

0.2 300µm 0.15 0.1

tf

0.05 0

0

1000

2000

3000

4000

t (s)

5000

6000

7000

8000

Fig. 7  a Picture of a square grooved surface with plateau thickness a = 100 µm, groove thickness b = 100  μm and groove depth c = 65  μm, collection area 20 cm2, side L = 14.7 cm, critical sliding radius ≈ mm, tilt angle with horizontal 45°, condensation rate h˙ = 0.1 mm.h−1 (adapted from Royon et al. 2016). Water contact angles on channel bottoms in Silicon are (advancing) 35° and (receding) = (32) b b c 2cosθB

Smooth substrates coated with alternate hydrophilichydrophobic stripes exhibit behavior similar to grooves (Chaudhury et al. 2014; Peng et al. 2014). Coatings are, however, sensitive to outdoor pollution by fat acids, which tend to remove the contrast of wetting properties between the stripes. The utilization of controlled, enhanced random roughness as performed by sand blasting on initially smooth surfaces (roughness δz = 0.5 µm) increases only weakly the hydrophilic or hydrophobic character of the substrate (Eq. 31) but, more importantly, gives a uniform array of nucleation sites (Fig. 4b). Sand blasted at p = 2  bar gives a roughness δz = 2 µm corresponding to the explosion of silica spheres of 25 µm diameter, with a surfacic density of ≈0.5 (Trosseille et al. 2019). The roughness factor r in Eq. (31) keeps close to unity, corresponding to a negligible increase of the drop pinning forces. However, the increase of nucleation sites cancels the dispersion observed on the non-blasted surface (Fig. 4b, c).

Superhydrophilic triangular patterns on superhydrophobic backgrounds have also been investigated (Hou et al. 2020). Such triangular arrangements can induce water movement due to a gradient of Laplace pressure gradient originating in a geometry-induced gradient, starting from the tip of the triangle and ending at its base. This process is similar to what happens with cactus spines (Ju et al. 2012).

Liquid-Imbibed Substrate (LIS) Liquid immiscible with water (oil) can be trapped in a microstructure. If oil has a low vapor pressure, such as silicone oil, it can remain trapped for a quite long time. Different situations occur depending on the different contact angles of the combination air, water and oil (Anand et al. 2012, 2015; Smith et al. 2013). Oil and water can partially or completely wet the substrate; oil can also engulf the water droplet and/or form an annular ring around it. Only 4 situations exist (Smith et al. 2013) where an oil wetting layer can isolate the drop from the surface making

Emerging Water Recovery Processes from Dew and Light Rain

21

shape must allow an easy collection of drops to be made. While more complex than planar structures, concave structures with angles larger than 30° with horizontal are thus more efficient to harvest dew water. 30° angle indeed corresponds to a gravity force still equal to the drop half-weight. Top edges, by allowing the early wiping of the drops by the fast growing drops on the edges, also enhances early drops collection. The shapes used so far are listed in Table 6; they are concerned with simple planar surfaces, ridges, eggbox-like structures, hollow cones pyramids, polygons and origamis.

8 Concluding Remarks

Fig. 8  Evolution of the condensed rate per surface area h on PDMS and infused PDMS (iPDMS) with different oil layer initial thicknesses. Condensation rate on PDMS is 0.1 mm h−1 (Adapted from Lavielle et al. 2022, with permission)

drops moving freely, without contact line pinning. The lag time to collect water is thus reduced to nearly zero. When oil engulfs water (see Sect. 2.4.2), drops are moving freely, however more oil is removed from the substrate. This removal has two consequences: (i) The microstructure will sooner or later lack oil and (ii) some oil is present in the collected water. The quantity of oil in water is however very low and can be simply removed by sedimentation. Other materials, like cross-linked PDMS swollen in silicone oil (PDMS oil), exhibit an oil interface of a few µm in thickness. Oil is slowly released, thus allowing long term use. In addition to favor droplet shedding, such materials increase the condensation rate at the beginning of condensation when compared with solid surfaces (see Fig. 8 where the rise is larger than 50%). This increase is due to a continuous nucleation of drops which are then immersed, leaving a free surface for further nucleation, as described in Sect. 2.4.2. Since a very small amount of oil is released in water (less than 0.05%), a few mm thick PDMS sheet once infused with PDMS oil (0.01 Pa s shear viscosity) can release oil for at least 5 years (Lavielle et al. 2022).

7 Dew Condenser Shapes The shape of the condenser can be adapted to remove the IR emission of the lowest layer of the atmosphere (typically less than 15°, see Sect. 2.1) and decrease the heat exchange with convected air (wind, see Sect. 6.1.2). In addition, the

Dew condensation occurs in many regions of the world, even in dry and arid areas. It needs a relatively clear sky (to benefit from radiation cooling) and atmosphere humidity high enough to keep a dew point temperature within a few degrees below the air temperature. The available cooling energy, below about 100 W m−2 K−1, decreases with the increase of atmosphere water content and the cloud coverage, which increases sky emissivity, and the wind speed, which increases the heat losses with the surrounding air. The maximum value is on order of 1 L m−2 day−1. This limit can be approached by using high emissivity materials and specific condenser shape that limits the heating IR radiations coming from the horizon and extend the condensation in the late afternoon and early morning. A model of dew condensation yield based on an energy balance between the radiative cooling energy and heating losses with surrounding air can be elaborated, using only air and dew point temperatures, wind speed and cloud coverage. From this model and data from meteo station, maps of dew potentials can be created, including projections in the future by using climate models data (see e.g. Muselli et al. 2022). Dropwise condensation is a general process for dew formation. The pattern of dew drops evolves while keeping universal self-similar properties. The pattern of drops of light rain and drizzle exhibit similar properties, the growth of the rain drops on the collecting surface being due to the incorporation of falling rain drops. Light rain and dew drops are difficult to collect by gravity because droplets remain pinned until they reach a critical size on the order of a mm, corresponding to a critical time lag and dead water volume. Film growth where water completely wets the surface shows similar behavior where water starts to flow after a time lag related to the film formation. Smooth and/or micropatterned substrates associated to well-designed shape of condensers decrease the critical lag time and the corresponding non-collected volume. Ideally, the lag time should be zero, which is the case for

22

some specific surfaces such as superhydrophobic or liquidinfused substrates, the latter however at the cost of minute oil in water. Condensing surfaces work under harsh outdoor conditions, and aging is a major problem. To date, the surfaces that exhibit the best resistance to aging are grooved polymer foils (also food proof) and paintings with special wetting and infra-red emissive additives (which can be made food proof). A review of the dew and rain chemical characteristics collected at the same site shows that the mean dew pH ~ 6.2 and rain pH ~ 5.6, ranging from (dew) 4 (Allegheny, USA) to 7.9 (Ajaccio, France) and (rain) 4.1 (Warren, USA) to 7.3 (Negev Nizzana, Israel). On average the pH value of rain is around one unit less than the dew pH at the same place. Electric conductivity varies much depending on the deposited aerosols, from (dew) 18 and 930 μS cm−1 and (rain) 18 and 390 μS cm−1 The concentration of dissolved ions is two times larger for dew than for rain, due to a lower dissolution effect. It is observed in many sites that dew and rain samples display approximately the same major cation distribution with + + the order Ca++  > Na+ > Mg2+ > NH+ 4  > K  > H for dew and + + 2+ ++ + Na  > Ca  > NH4  > Mg  > K for rain. The same remark holds for the major anions, showing the similar trend in dew and − − rain Cl− ≫ SO2− 4  >  NO3  > NO2 . Ions can be of marine origin (Na+, Cl−, Mg2+), soil origin (Ca2+, K+), or anthropic origin 2− − − (NH+ 4 , SO4 , NO3 , NO2 ). In general, the ion concentrations are low enough to fit the WHO requirements for potable water. Biological analyses of rain and dew water are very few and cannot be considered as conclusive. Dew and rain samples show the presence of microorganisms of vegetal origin developing at 22 °C > 300 CFU/ml and of animal and/or human origin developing at 36 °C > 300 CFU/ml. If simple care is taken for sampling and collection, microorganisms, unsurprisingly, become much less numerous.

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Capacitive Deionization: A Promising Water Treatment and Desalination Technology Myriam Tauk, Marc Cretin, Mikhael Bechelany, Philippe Sistat and Francois Zaviska

Abstract

Keywords

Since the 1960s, the research community exploring electrochemical water treatment methods has shown considerable interest in Capacitive Deionization (CDI). The operational model of this technology relies on the adsorption of ionic constituents onto high surface area electrodes, facilitated by the application of a low voltage across the system. This voltage initiates the generation of an electric field, propelling ions toward their respective countercharged electrode. These ions will be temporarily stored inside the electrical double layers (EDLs) of the porous electrodes, thereby resulting in water deionization. After saturation, these electrodes will subsequently desorb the solvated ions when the potential is switched off. Unlike other membrane and thermal desalination techniques like reverse osmosis (RO) and multi-stage flash distillation (MSFD), CDI technology interestingly targets the solutes instead of the solvent. This makes it a highly effective desalination technology for brackish water consuming less energy with a driving electric force of low 1.0–1.4 V potential with the possibility to control the desalination rate simply by adjusting the hydraulic retention time and electrical charge (cannot be done with other membrane or thermal-based desalination technologies). This chapter reviews capacitive deionization as an electrochemical water desalination technology, its theoretical and technological aspects, the history of its development, its material and architectural aspect with extension to its counterparts which are membrane capacitive deionization (MCDI) and flow electrode capacitive deionization (FCDI), and attempts toward its optimization for scaling up and commercialization. This chapter also presents a critical review of the technology’s advantages and limitations.

Water desalination · Electrosorption · Ion adsorption · Carbon electrode · Capacitive deionization

M. Tauk · M. Cretin · M. Bechelany · P. Sistat · F. Zaviska (*)  Université de Montpellier, Montpellier, Francee-mail: francois. [email protected]

1 Introduction The shortage of freshwater has become one of the main alarming problems nowadays affecting every continent in the world. In the last century, global water consumption has been growing at twice the rate of human population growth. More than 1/5 of the global population live in countries experiencing water stress already (UN 2018). This strong pressure on the water resources will continue to increase as climate change affects water systems, industrial agriculture expands, and urban areas rapidly grow. Sea water constitutes 98% of the total water on our planet. This saline water is not directly available for human consumption, but it can be treated for this purpose. Desalination technologies are numerous. We can site membrane-based technologies like reverse osmosis (RO), thermal-based technologies like multi-stage flash distillation (MSFD) and multi effect distillation (MED), and electrochemical water desalination technologies such as electrodialysis (ED). These water desalination techniques represent potential solutions for the actual freshwater crisis, the reason why they are gaining important interest in the water treatment research field. The number one technology used globally nowadays for seawater desalination is RO accounting for 64% of the total desalination industry in the world. MSFD has also been with RO in the front line of major water treatment plants worldwide with 23%. MED and ED account for 8% and 4%, respectively (Borsani and Rebagliati 2005). Electrochemical water desalination technologies such as ED are promising candidates in the desalination field

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 K. Jlassi et al. (eds.), Clean Water: Next Generation Technologies, Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-031-48228-1_2

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mainly for their low energy consumption. This kind of desalination technique has many advantages. Unlike membrane- and thermal-based desalination technologies (RO and MSFD), electrochemical desalination removes salt from water and not the opposite. This makes it more energy efficient for low and moderate salinity streams like brackish water with very low electrical potential as driving force of the system. Electrochemical desalination has also the advantage of controllable desalination rate making it possible to control the ion concentration in the desalinated stream. Another innovative electrochemical desalination technology attracting big research interest in the last decade is capacitive deionization method (CDI) which the desalination principle is based on in the ion adsorption process. CDI represents a developing technology aimed at electrically extracting charged particles from liquid solutions. Through the utilization of an external power source, an electrode becomes electrified, compelling ions to adhere within the electric double layer (EDL) formed at the junction of the electrode surface and the electrolyte solution. In other words, it’s an electrosorption method that uses sorption media with the application of an electrical field to separate ions. This growing technology has been formerly used for brackish water desalination (water with salt concentration below 10 g/L) (Gabelich et al. 2002), sea water desalination (Tang and Zhou 2020), water softening (Leong and Yang 2020), and wastewater treatment (Kalfa et al. 2020). Different aspects have been interestingly investigated during the last decade in the field of CDI, involving theoretical (Biesheuvel et al. 2011a, b, 2014), architectural (Tang 2018; Suss et al. 2012; Porada et al. 2012a; Oren and Soffer 1978; Lee et al. 2014), and material aspect (Folaranmi et al. 2021, 2022; Alhan et al. 2019; Cheng et al. 2019; Zhao et al. 2020). A typical CDI system comprises a pair of porous carbon electrodes. These electrodes can be immobile or configured for fluid passage, and they are situated at a certain distance from each other. The influent water can flow between these polarized electrodes or permeate through them. Upon the application of a voltage, typically within the range of 1–1.4 V, ions within the source solution experience electrostatic migration toward the electrodes of opposing polarity. Subsequently, these ions are sequestered within EDLs that form at the interface connecting the electrodes and the water. This process is known as electrosorption. Ions will hold on to the EDLs until the discharging step takes place after electrode saturation where the polarity will be reversed. Through this discharge step, ions will be released back into the water generating what is called the brine stream or concentrate. To note that the charge leaving the CDI cell during the desorption step can be leveraged as recovered energy (Długołęcki and Wal 2013).

M. Tauk et al.

2 History First studies on CDI started in the 1960s and early 1970s. The first work on CDI-type system presenting the concept of electrochemical water deionization using a sorption media was firstly reported by John W. Blair and George W. Murphy in January 1960 with a publication entitled “Electrochemical Demineralization of Water with Porous Electrodes of Large Surface Area (Blair and Murphy 1960).” Later in 1971, Johnson and Newman introduced ion transport theory in porous carbon electrodes and ion storage with a capacitor mechanism, and also studied the reversibility of this process (Johnson and Newman 1971). Johnson’s research group proceeded a preliminary cost evaluation for this process, showing that it can indeed achieve efficient and cost-effective desalination, and provided that high surface area stable electrodes can be developed. From the 1990s onward, capacitive deionization concept began to draw more attention, mainly with the development of new electrode materials, namely carbon nanotube electrodes and carbon aerogels (Farmer et al. 1996). In 1996, the term capacitive deionization with the “CDI” abbreviation was used for the first time when introduced by Farmer et al. (Farmer et al. 1995) Conversely to the slow early development of this technology, enormous advances were observed in the last decade leading to the fast development of CDI. In 2004, with a patent, Andelman introduced the concept of Membrane Capacitive Deionization (Andelman et al. 2004). Other advances followed, including the development of flow-through electrodes,10 flow electrodes (Folaranmi et al. 2022; Porada et al. 2014; Hatzell et al. 2014), hybrid CDI (Lee et al. 2014), the finding of the correlations between pore size and electrosorption performance (Porada et al. 2013a; Tsai and Doong 2015), and the correlation between particle size and desalination performance Byles et al. (2008). In parallel, the development of commercial products using CDI technology by different global companies is taking place.

3 Principle A CDI unit comprises a pair of carbon electrodes, positioned with a gap through which the incoming water passes. Depending on the specific design of the unit (as shown in Fig. 1), the water can flow amidst the carbon electrodes or penetrate through them. Upon applying a potential difference of 1–1.4 V to the unit, the charged electrodes attract the ions present in the incoming water through electrostatic forces. These ions are subsequently stored within EDLs on the surface of the electrode pores, at the electrode/electrolyte interface. This process, known as “electrosorption,”

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Fig. 1  Schematic diagram of CDI system set up

effectively removes salt from the incoming water. The ions remain firmly held within the EDLs due to electrostatic interactions. If the external voltage is either disconnected or its polarity is reversed, these ions are released back into the incoming water, leading to the creation of a concentrated salt solution referred to as a “brine stream.” This discharging step is essential for electrode regeneration when electrodes are saturated or when the desalination rate becomes too low. Interestingly, the charge leaving the cell during the discharging step can be recovered (partial energy recovery during discharge). Adsorption and desorption steps are represented in Fig. 2a and b, respectively. During the adsorption step (Fig. 2a), the solvated ions are electrostatically attracted to the oppositely charged electrodes, as a result, positive and negative ions are separated producing fresh water. On the other hand, during the desorption step (Fig. 2b), brine stream is generated after the release of ions from the pores of the electrodes once the Potential is turned off.

3.1 Ion Adsorption Mechanism 3.1.1 Capacitive Ion Adsorption The process of capacitive deionization is rooted in the principle of electrosorption, which centers on the mechanism of ion storage within the pores of the electrode, specifically within the EDLs. A particular type of CDI apparatus, which operates on the basis of electric double-layer capacitors, comprises two electrodes. When a potential difference is applied to the CDI cell, the accumulation of ions is

propelled electrostatically toward the electrodes, particularly at the interface between the electrode and electrolyte. This phenomenon creates what is known as the electrical double layer (EDL), embodying the ion adsorption process in CDI. Back in 1883, Helmholtz (Meunier et al. 2010) introduced a model for ion adsorption in capacitors, suggesting that the distribution of charge within the EDL is governed by the accumulation of ions with one sign at the surface of the electrode bearing the opposite charge, while ions carrying the same charge are dispersed (with lower accumulation) on the solution side (Folaranmi et al. 2020). In accordance with the Gouy–Chapmann–Stern model, the EDL is divided into two regions: an inner area referred to as the Helmholtz layer, where ions amass near the surface of the charged electrode, and a diffusion region termed the Gouy–Chapmann layer. The latter is located farther from the electrode’s surface and showcases a more dispersed arrangement of ions. Within this layer, the distribution of electric charge is contingent upon the potential at the electrode's surface (see Fig. 3 for visual representation).

3.1.2 Pseudocapacitive Mechanisms As previously elucidated, the process of ion adsorption transpires at the electrode's surface, specifically at the interface connecting the electrode and electrolyte. Consequently, the surface area of the electrode stands as a pivotal factor influencing both ion storage capacity and ion transfer rate. In CDI systems employing these electrodes, the range of applicability was constrained to lower concentrated brine due to the finite salt adsorption capacity of porous carbon-based electrodes. These electrodes, driven

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Fig. 2  Diagram of CDI adsorption step (a) and desorption step (b)

Redox Pseudocapacitance Redox pseudocapacitance refers to a remarkably reversible redox reaction occurring at or in close proximity to the electrode surface, entailing a Faradaic charge exchange between the ions present within the electrolyte solution and the solid electrode (Rochefort and Pont 2006). This phenomenon is notably prevalent in transition metal oxides (TMOs), which serve as frequently employed pseudocapacitive materials in this domain. Within these electrode materials, a Faradaic mechanism triggers reversible redox reactions either directly at the surface or slightly below it (in the vicinity of the surface). This process leads to an exceptionally elevated capacitance level, thereby facilitating the storage of charge (Ma et al. 2019).

Fig. 3  Charges distribution in EDL according to Gouy–Chapmann model

by potential-induced adsorption, electrostatically capture ions. On the other hand, here, the ion storage mechanism is that of pseudocapacitor or Faradaic ion storage so-called desalting battery Gamaethiralalage (2021). Redox-active electrode materials based on Faradaic ion storage offer higher specific capacitance and deionization capacity making it possible to desalinate higher salinity streams (Zhao et al. 2022). Pseudocapacitive mechanisms are of two main types: redox pseudocapacitance and intercalation pseudocapacitance (Augustyn et al. 2014).

Intercalation Pseudocapacitance The intercalation pseudocapacitance mechanism involves the insertion of ions between the layers of the redox-active material functioning as an electrode. This process is facilitated by a Faradaic charge exchange, all without causing any alterations in the crystallographic phase of the material being utilized (Han et al. 2019). This mechanism draws a parallel to the ion intercalation process seen in lithium-ion batteries, although in the latter case, such intercalation typically coincides with a phase transition (Kuhn et al. 2022). For this pseudocapacitance mechanism to be effective, the chosen material must possess a crystal structure that enables swift ion diffusion pathways. Additionally, the material must exhibit substantial stability to ensure that no changes in its structural arrangement occur during the ion intercalation process.

Capacitive Deionization: A Promising Water Treatment and Desalination Technology

29

3.1.3 CDI Classification Based on the Ion Storage Mechanism

4 Advantages of CDI

Conventional Capacitive CDI This CDI form is made by capacitive anode and cathode separated with a spacer through which feed water flows. The anode and cathode in this case are composed of carbon material and store ions in the EDLs through capacitive mechanism as explained previously (Tang et al. 2019).

CDI has many unique advantages over other desalination technologies. First, unlike membrane or thermal process, CDI is based on electrical potential as the driving force to separate ions in saline solution and thus does not require high-pressure pump or heaters, which makes it a low cost technology from investment and infrastructure point of view. This allows uncomplicated system scaling, and less energy-consuming desalination process. Second, unlike other desalination technologies, such driving force targets the solutes instead of the solvent which makes it possible to control the desalination rate by simply adjusting the hydraulic retention time (HRT) with the electric charge applied. Hence, this technology appears to be more energy efficient for low and medium salinity feed streams (3

IB: inlet of the biological reactor OB: outlet of the biological reactor

234

zeolite and NaCl electrolyte. The efficiency of the process was assessed by monitoring several parameters such as the electrical conductivity, turbidity, COD, total Kjeldahl nitrogen (TNK), total solubility, total solids and temperature of the treated solutions. The authors have used the Taguchi approach for the optimization of the leachate processing. The impact of agitation rate, spacing between Al electrodes, added NaCl and zeolite, and initial pH setting of the solution were varied in order to evaluate their effect on the Chemical Oxygen Demand, turbidity, TNK, sedimentation rate and electrode wear. It was concluded that the optimal value of a given parameter is highly dependent on the goal to be achieved, and that treatment efficiency is closely related to each of the parameters studied. Taguchi optimization has illustrated that the stirring speed is the most influential factor for COD, TNK, and turbidity. Nevertheless, the NaCl use has resulted in settling rate and electrode loss. On the other hand, the authors found that the electrode’s distance variation has a relevant impact only on electrode loss. However, the supplementary biosorption treatment using Zeolite improved COD removal but it has been inefficient in the elimination of TNK, turbidity, settling rate, and electrode loss. They found that by fitting the pH to 4, an optimal elimination of COD, TNK, turbidity, and lower electrode loss is achieved. Through this study, it was concluded, that the optimum conditions cannot be consistently determined. Hence, a unique process treatment using EC is adequate for some physicochemical parameters, whereas, the combined processes of EC and biosorption are efficient for other factors.

3 Electrocoagulation Process Coupled to Membrane Separation For highly-polluted effluents, such as brewery wastewater, Dizge et al. (2018) investigated the efficiency of the combination of electrocoagulation (EC), ultrasonication (US) and sono-electrocoagulation (SEC) process treatment. In order to enhance the overall performance of the system and to ensure continuous processing, they have implemented a cross-flow membrane system. The efficiency of the treatment was expressed in terms of colour and chemical oxygen demand (COD) maximum removal of 99.2 and 60.5%, respectively, which were obtained for the optimum conditions of the current density of 100 A/m2, pH 7.0, and reaction time of 60 min and using aluminium sacrificial electrodes. In this context, two membrane processes were evaluated such as nanofiltration (NF) and reverse osmosis (RO) membranes leading to the conclusion that the coupled sono-assisted electrocoagulation and membrane system can be successfully applied for the brewery wastewater treatment. The additional treatment using membrane systems

E. S. B. H. Hmida et al.

improved the COD removal by 50% with a combined process of sono-assisted electrocoagulation and reverse osmosis. In an additional work, Sardari et al. (2018) have tested the performance of coupling the electrocoagulation process with membrane distillation for the treatment of high salinity hydraulic fracturing produced water (HFPW). The authors have studied the implementation of the electrocoagulation process as a pretreatment step in order to remove the suspended solids and organic substances for real HFPW samples. In fact, in the case of concentrated streams of HFPW highly charged with surfactants, soluble organic substances and total dissolved solids (TDS), a prior treatment step is strongly recommended to avoid membrane fouling. The authors tested the EC-DCMD process for feed streams with TDS ranging from 135 g L−1 TDS, up to 265 g L−1. The treatment system thus developed showed optimal running for 434 h, with much reduced membrane fouling. In a recent paper Tang et al. (2022) have studied the current advancement regarding the coupling of membrane separation and electrocoagulation process. In this work, the authors applied the membrane separation, for the removal of pollutants, with high permeability and antifouling capacity for its large-scale application. This was achieved by coupling the electrocoagulation process with a membrane filtration process. Tang and co-authors have introduced a conductive film (Sb-SnO2) on the ceramic membranes to overcome membrane fouling problems. Following this modification, they found that fouling became reversible. It was then demonstrated that the conductive ceramic membrane cathode incorporated in electrocoagulation makes a significant contribution to minimizing membrane fouling, and that the newly developed system offers great promise for the treatment of large-scale effluents.

4 Conclusion Electrocoagulation is the process of choice for effluent treatment, the simplest, least expensive and easy to apply on a large scale. It has proven its effectiveness in the elimination of various pollutants from wastewater, including organic substances, heavy metals, oil and fats, colloids and dyes by applying electric current through sacrificial electrodes. Apart from the complexity of the reactions taking place in situ and which are at the basis of the removal of pollutants in the form of floating sludge, its efficiency can be greatly improved by combining the EC process with other physical and chemical processes which can generate water of high quality for industrial, irrigation or domestic use. Actually, the development of combined processes

Electrocoagulation

associating electrocoagulation and electrochemical, adsorption and membrane-based processes is becoming increasingly relevant in the field of environmental applications of electrocoagulation. This is an important aspect that can make electrocoagulation a good alternative for water and wastewater treatments even for the most recalcitrant pollutants. Nevertheless, the major factor to be considered is not only the energy consumption but also the total cost of the process.

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Removal of Organochlorine Pesticides from Soil and Water Carmen M. Domínguez, Alicia Checa-Fernandez, Raúl GarcíaCervilla, David Lorenzo, Salvador Cotillas, Sergio Rodríguez, Jesús Fernández and Aurora Santos

Abstract

The intensive production of the organochlorine pesticide lindane (γ-hexachlorocyclohexane) caused vast amounts of HCH isomers’ residues during the past century’s second half. These residues were usually deposited or discharged in uncontrolled landfills close to the factories, generating soil and groundwater contamination hot spots. Large lindane-contaminated sites have been categorized in Europe, Asia, Africa, and Asia. The legacy of lindane production caused a substantial environmental problem that has not been solved yet. Solid and liquid residues generated as lindane wastes have caused contamination of topsoil and groundwater, and the remediation treatments applied should consider the type and location of this contamination. Two of these sites are located at Sabiñánigo (Spain), where two landfills, Sardas and Bailín, were contaminated with HCH-wastes by INQUINOSA, a lindane factory operating from 1975 to 1988. This chapter reviews some “on-site” and “in situ” chemical technologies recently proposed to remediate this site.

Keywords

Sabiñánigo · Lindane · HCH · DNAPL · Groundwater ·  Soil · Remediation · Surfactant · SEAR · ISCO ·  ISCR · ZVI · AOP · Persulfate · Activation

C. M. Domínguez (*) · A. Checa-Fernandez · R. García-Cervilla · D. Lorenzo · S. Cotillas · S. Rodríguez · A. Santos  Chemical and Materials Engineering Department, Faculty of Chemical Sciences, Complutense University of Madrid, Ciudad Universitaria S/N, Madrid, Spain e-mail: [email protected] J. Fernández  Agriculture, Livestock and Environment Department, Government of Aragon, Zaragoza, Spain

1 Introduction Pesticides are substances used to kill, repel, or control certain forms of plant or animal life considered pests (https:// www.niehs.nih.gov). These substances include herbicides, insecticides, fungicides, disinfectants, etc. Pesticides became a critical component of worldwide agriculture systems during the last decades since they allowed for an evident increase in crop yields and food production (Carvalho 2017; Jayaraj et al. 2016). Pesticides that can no longer be used for their intended function or want to be used become obsolete and must be disposed of Shah and Devkota (2009). The term “obsolete pesticides” is defined as pesticide waste comprising specific chemicals unwanted due to overstocking or deterioration and/or outlawed for environmental and human health reasons (Vijgen et al. 2013). In recent decades, unsustainable pesticide life-cycle management has created large stockpiles of obsolete pesticides worldwide (Vijgen et al. 2013). Most of these substances are considered persistent organic pollutants (POPs) by the Stockholm Convention (http://chm.pops.int). The physical and chemical properties of POPs make sure that once these compounds are released into the environment, they can be widely distributed, remain unchanged for extremely long periods, and accumulate in the adipose tissue of living organisms (their concentration increasing by up to 70,000 times the background levels). POPs are a primary environmental concern due to their persistence in the environment, long-range transportability, bioaccumulation, and adverse effects (acute and chronic toxicity) on animals and humans (Xu et al. 2013). Specific effects of these pollutants include diseases like cancer, allergies and hypersensitivity, damage to the central and peripheral nervous systems, reproductive disorders, and immune system disruption. Some POPs are also endocrine disrupters and damage the reproductive and immune systems of exposed individuals and their offspring. Organochlorine pesticides (OCPs) have been widely used over the world during the past century (around 40%

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 K. Jlassi et al. (eds.), Clean Water: Next Generation Technologies, Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-031-48228-1_16

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of the pesticides used are chlorinated (Jayaraj et al. 2016)). These compounds are chlorinated hydrocarbon derivatives with considerable applications in the chemical industry and agriculture (Jayaraj et al. 2016). They are classified as POPs, with high environmental persistence. Therefore, they represent a tremendous environmental concern nowadays. Organochlorine pesticides include DDT, DDD, dicofol, aldrin, dieldrin, chlorobenzoate, lindane, BHC, methoxychlor aldrin, chlordane, heptachlor, endosulfan, isodrin, isobenzan, toxaphene, and chloropropylate. OCPs can enter the environment because of direct pesticide application, pesticide-polluted wastes dumped into landfills, and accidental discharges from industrial units. Lindane (the gamma isomer of hexachlorocyclohexane, γ-HCH) is one of the pesticides most used in developing countries, making this compound (and the other HCH isomers) one of the most commonly found chlorinated contaminants in the environment (Bhatt et al. 2009). The synthesis of γ-HCH (progressive photo chlorination of benzene with UV light) is an inefficient process, generating between 8 and 12 tons of waste for each ton of lindane produced, including solid HCH-wastes (HCH isomers) and liquid wastes from the chlorination failed reaction, distillation tails and emptying of the production pipes (solvents residues, HCH isomers, chlorobenzenes and other chlorinated compounds) (Fernández et al. 2013; Santos et al. 2018a). The first step of the synthesis generates a combination of HCH isomers known as technical-HCH, with only 10–15% of lindane (Fernández et al. 2013; Wacławek et al. 2019). After that, γ-HCH is separated from the rest of the HCH isomers and purified by fractional distillation using organic solvents to obtain lindane with a purity greater than 99.5%. The wastes generated during lindane synthesis were usually dumped, without environmental concerns, in the

vicinity of the production sites (Santos et al. 2018a, 2020; Vijgen 2006), greatly contaminating the surrounding soil and groundwater. Thus, it is estimated that around 5 million tons of lindane waste spread worldwide, leading to the world’s largest POP stockpile (Fernández et al. 2013; Vijgen et al. 2011). The pollution sites cover countries such as Argentine, Brazil, China, the Former Soviet Union, India, Japan, South Africa, the United States, and especially, European countries (Czech Republic, France, Germany, Hungary, Italy, Japan, Poland, Romania, Slovakia, Spain, Switzerland, Turkey, the Netherlands, UK) (Vijgen et al. 2011, 2013), where 63% of total waste is concentrated. The location of these polluted sites and the estimated quantity of HCH waste dumped in those places is shown in Fig. 1. As a result of lindane danger (high persistency, bioaccumulation, and harmful effects on human health and the environment), its production and use have been prohibited in most countries. Along α-HCH and β-HCH, the Stockholm Convention included lindane in the list of POPs (Vijgen et al. 2011). The recent report published by the Directorate-General for Internal Policies on lindane residues in the European Union gives an idea of the concern of citizens and authorities about this environmental problem (Vega et al. 2016). Therefore, developing viable treatments for removing these pollutants has become a primary concern for the scientific community. Different approaches should be developed to the complex environmental problem of these polluted sites. Chemical treatments (oxidation and reduction) of HCHspolluted soil and groundwater can be applied: (i) In situ (in situ chemical oxidation, ISCO or in situ chemical reduction, ISCR), injecting an oxidant

Fig. 1  Location and quantities of stored/dumped HCH waste around the world

Former Soviet Union (250000)

Europe (>1500000)

US (65000)

China (91200)

Brazil (50000)

Argentine (unknown)

India (56000)

South Africa (70000)

Japan (76000)

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241

or a reductant in the subsurface for transforming Chlorinated Organic Compounds (COCs) into less harmful chemical species, (ii) Ex situ, where the polluted soil/groundwater is removed/pumped from its location, transported and, finally, treated; or (iii) On-site (also known as off-site), where the polluted samples are treated in the original site, preventing dangerous and costly soil or water transposition from the landfills.

2 Sabiñanigo Landfills (Bailín and Sardas): Sites Characterization The pesticide lindane was produced in Spain in the Basque country (≈82,000 tons of waste), in O Porriño, Galicia (thousand tons of HCH-waste and HCH-polluted soil) and in Sabiñánigo, Huesca (≈115,000 tons of HCH-waste) (Fernández et al. 2013). They all ceased production decades ago, with the last plant (INQUINOSA) operating until 1988 (Fernández et al. 2013). The case of Sabiñánigo, a small industrial city of Huesca (Fig. 2), where INQUINOSA (the largest producer of lindane in Spain) operated from 1975 to 1988 has been used to develop technologies that can remediate contamination due to HCH wastes. It can be considered a mega site contaminated by HCH waste, resulting in massive soil and groundwater pollution, with the risk of contamination of the Gállego River. Figure 2 shows the geographic location

of Sabiñánigo and includes a photograph of the city and the Gállego River, the old INQUINOSA factory, and the two landfills, where lindane waste was dumped and which remain contaminated nowadays: Sardas and Bailín landfills. INQUINOSA is the acronym of Industrias Químicas del Noroeste Sociedad Anónima. The old factory is located between the Aurin River terrace and the alluvium of the Gállego River, and an access road separates it from the Sabiñánigo reservoir. The company manufactured and commercialized lindane from 1975 to 1988, generating different types of waste, firstly dumped in the Sardas landfill (from 1975 to 1983) and later in the Bailín landfill (from 1984 to 1992). During the INQUINOSA operation, it is estimated to discharge 7,000 tons of solid waste annually, and between 300 and 600 tons of liquid waste were produced. Disposing of these wastes has caused a highly contaminated site ((Fernández et al. 2013), www.stoplindano.es). Figure 3 includes a scheme of the sources of contamination (solid and liquid wastes) and the subsequent types of pollution associated (superficial soil, runoff water, leachate, DNAPL, groundwater, and subsoil) (Fernández et al. 2013). – The solid waste comprises α-HCH, β-HCH, δ-HCH, and ε-HCH (γ-HCH was previously separated from the HCH mixture by distillation). The deposition of these residues, mainly during the first years of factory operation, is associated with superficial soil contamination (and the associated superficial water and leachate) (Fig. 3).

Fig. 2  Location of the industrial city of Sabiñánigo, the lindane producer factory (INQUINOSA), and the polluted landfills in the surrounding city: Sardas and Bailín

Sabiñánigo (Huesca)

Spain

INQUINOSA factory

Sardas landfill

Bailín landfill

242 Fig. 3  Sources and types of contamination in the Bailín and Sardas landfills (Sabiñánigo)

C. M. Domínguez et al.

Solid Wastes (Technical-HCH)

Disposal of lindane wastes in unlined landfills Liquid wastes (DNAPL)

α-HCH β-HCH Leachate

DNAPL migration (ρ=1.5-1.8 g ml-1)

HCH particulate matter DNAPL solubilization

Polluted SUBSOIL

GROUNDWATER plume

DNAPL pool

Water table

Vadose zone

GROUNDWATER flow

DNAPL adsorption 28 Chlorinated Organic Compounds (COCs)

– The liquid waste originated in failed reactions for lindane synthesis, and the distillation tails are composed of HCHs, benzene, different chlorobenzenes and other chlorinated compounds, and solvents traces. Due to the physicochemical characteristics of these compounds, this waste constitutes a dense, nonaqueous phase liquid (DNAPL). The density of this organic phase (higher than the water density) and its hydrophobic nature caused the dumped DNAPL to go down under the groundwater table. The DNAPL accumulated in the impermeable layers through its travel, generating a groundwater plume of contamination (Fig. 3) involving a related risk for the nearby river and reservoir (Fernández et al. 2013; Navarro et al. 2000). This liquid waste was discovered in 2005 at around 30 m from the Sabiñánigo’s reservoir. After that, it was detected in Sardas and Bailín landfills at very variable depths, even on the surface (Fernández et al. 2013; Casado et al. 2015). When the factory closed (1992), no environmental measures were taken. Consequently, INQUINOSA remains an industrial ruin, with rests of toxic wastes inside, probably affecting the soils and structures of the factory. The Aragon Government recently implemented a strategy to remediate this site (www.stoplindano.es). Sardas landfill is less than 1 km from Sabiñánigo, extending around 4 ha beside the Gállego River. It is calculated that between 50,000 and 80,000 m3 of HCH solid waste and 3,000 m3 of DNAPL were dumped in this

Impermeable bedrocks

Saturated zone

landfill. The landfill lacked a liner system in its basin and had no leachate treatment or other protective methods. The generated leachates and waste dispersion are responsible for soil, groundwater, and surface water contamination. Moreover, a DNAPL pool has been detected downstream of the Sardas landfill (Fernández et al. 2013; Santos et al. 2019). After its abandonment, a new landfill close to the Bailín ravine started to be used for dumping INQUINOSA waste: the Bailín landfill, with a surface of around 3 ha. Around 200,000 m3 residues (HCH solid waste, DNAPL, and contaminated soil) were dumped in this landfill. This landfill constitutes an environmental problem due to the complex geological and topographical area (alternation of sub-vertical layers of conglomerates, sandstones, and siltstones) in which it is located and the isolation lack. Consequently, the rock mass and the groundwater are contaminated, generating a contamination plume in the Gallego River direction. The Regional Government of Aragon is managing this enormous environmental problem in collaboration with several public and private companies in the sector and universities. Aragon Government has developed a strategic plan to eliminate and control this contamination in the two landfills and the INQUINOSA factory (www.stoplindano.es). Among all the pollutants hosted by the landfills, DNAPL stands out (a problem not commonly described in other hot sites polluted with HCHs waste (Santos et al. 2018a; Lorenzo et al. 2020). As previously stated, this dense phase percolates through the rock fractures (Bailín landfill) or the

Removal of Organochlorine Pesticides from Soil and Water

alluvial and fractured marls (Sardas landfill). DNAPL may be liquid puddles or adsorbed/trapped in the soil (Fernández et al. 2013; Lorenzo et al. 2020). DNAPL solubilization in the groundwater significantly pollutes it, which implies a high risk for the nearby river and reservoir (Fernández et al. 2013; Navarro et al. 2000). Therefore, as long as DNAPL remains in the subsoil, it will constitute a groundwater source of contamination. The composition of this contamination plume is determined by DNAPL composition, COCs solubility, and/or the partitioning behavior between both phases, DNAPL and water (Santos et al. 2018a; Lorenzo et al. 2020). The DNAPL consists of a mixture of 28 COCs from chlorobenzene to heptachlorocychlohexane, many noncommercial (Santos et al. 2018a). Owing to its high density (>1.5 g cm−3) and infiltration capacity, DNAPL locating and extracting are complicated. The complete chemical characterization of this phase is required to select the best treatment strategy. In this line, Santos et al. (2018a, b) determined the whole organic composition of six DNAPLs obtained from the Sabiñanigo landfills (Santos et al. 2018a). They were black-brown viscous liquids with a chemical characteristic smell. The contaminants identification and quantification were carried out by gas chromatography, using different detectors: Mass Detector (MSD), Flame Ionization Detector (FID), and Electron Capture Detector (ECD). The content of HCH ranged from 22 to 30% in weight, lindane (γ-HCH) and δ-HCH being the isomers with the highest concentration, followed by α-HCH, whereas β-HCH was the least concentrated isomer. Chlorobenzene (CB), isomers of different chlorobenzenes (dichlorobenzene (DCB), trichlorobenzene (TCB), and tetrachlorobenzene (TetraCB)) and non-aromatic COCs (pentachlorocyclohexene (PentaCX), hexachlorocyclohexane (HexaCX), and heptachlorocyclohexane (HeptaCH)) were also identified and quantified. The HCH residues are heavily polluted with dibenzo-p-dioxin/dibenzofuran, PCDD/ Fs (1488 ng WHO2005-TEQ/kg, World Health Organization Toxic Equivalent), and even higher values were found in the DNAPL (37,353 ng WHO2005-TEQ/l). The PCDD/Fs contamination was lower in landfill leachates (5.8–30.7 pg ng WHO2005-TEQ/l), sediments, and soils (0.3–24.6  WHO2005-TEQ/kg) (Gómez-Lavín et al. 2018). The following sections summarize the research developed by researchers of the INPROQUIMA group (www. inproquima.es), collaborating with the Aragon Government and companies such as SARGA and EMGRISA to develop chemical technologies for the remediation of Sabiñanigo landfills or similar sites polluted with wastes from lindane production. In this context, it is worth mentioning the LIFE SURFING project, a demonstrative project coordinated by the Aragon Government in which the implementation of treatments combining chemical oxidation techniques and

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surfactants for the decontamination of the Bailín landfill subsoil (removal of dense residues adhering to the bedrock walls) is currently being carried out (www.lifesurfing.eu). The application of these technologies implies the use of chemicals, namely oxidants (hydrogen peroxide, persulfate), reductants (zero-valent iron microparticles), catalysts (iron, ferrioxalate, goethite), activators (NaOH), surfactants, etc. These compounds do not pose, in general, a relevant environmental risk for water or soil. In the case of on-site treatments, the final destination of the treated water must be taken into account, and if any of the compounds or properties exceeds the permitted discharge limits (iron, conductivity, etc.), the treated water must be conditioned prior to discharge, as with any other chemical treatment. In the case of in situ treatments, the remaining reagents in the subsoil should not cause an environmental hazard since they would be progressively consumed over time (continuing the degradation process in the long term) due to the groundwater flow. Adding large concentrations of salts to the subsoil (PS, NaOH…) could modify its permeability and microbiology. In this sense, studies in which biological treatments are applied to soils previously treated by chemical processes are being carried out. In any case, these treatments have been applied to remediate highly polluted soils whose purpose will not be agricultural, so modifying these soil properties is not a limitation. The composition of one of the DNAPLs used in the following works has been detailed in Table 1-a (Santos et al. 2018a). This table also collects the information concerning the chlorinated organic compounds identified and quantified in groundwater saturated by the contact with DNAPL, “GW-sat-DNAPL” in Sardas landfill (b) (Lorenzo et al. 2020), the COCs composition of contamination plume in Sardas alluvial caused by transport of the groundwater saturated in DNAPL, “GW” (c) (Santos et al. 2018b), the soil of Sardas alluvial impacted by DNAPL, “Subsoil” (dp  12)

Pollutant

SEAR surfactant enhanced aquifer remediation, m.b.g.l. meters below ground level, Øp particle diameter, VL/WS  liquid/soil phase ratio (VL in ml and WS in g), COC chlorinated organic compound, surf surfactant, DNAPL dense nonaqueous phase liquid, E3 E-Mulse® 3, T80 Tween®80, TS80 a mixture of Tween®80-Span®80, SDS sodium dodecyl sulfate, MSR molar solubilization ratios, SFS surfactant flushing solution, S-ISCO surfactant-enhanced in situ chemical oxidation, PS persulfate, CMC critical micellar concentration

Subsoil (14 m.b.g.l., Batch (VL/ WS = 10, 3.5 g Sardas’s landfill) Øp = 0.25–2 mm (F) of soil) and 80% was obtained after 144 h and 48 h, respectively. The oxidation of chlorobenzenes by hydroxyl radicals was more favored than that one of non-aromatic compounds (pentachlorocyclohexenes, hexachlorocyclohexenes, heptachlorocyclohexanes, and hexachlorocyclohexanes). The surfactant degradation was significantly lower than the oxidation of COCs. In this sense, the surfactant capacity remained after the oxidation process, allowing its reuse for further flushing steps to improve the process’s economy (Dominguez et al. 2019). Thus, applying the SEAR process with a nonionic surfactant followed by the selective oxidation of COCs using Fenton’s reagent is a helpful alternative for the remediation of the remnant fraction of DNAPL in the landfill’s subsoils. However, the technology scaling needs extra analyses to find the optimal conditions for each process step. In this line, several aspects should be carefully evaluated before SEAR application in the polluted site, such as the chemicals transport into the subsoil, surfactants adsorption, fluid injected dispersion, and DNAPL mobilization. For that purpose, some pilot tests were carried out in the Sardas landfill to characterize the subsoil flow: the first one using only a conservative tracer (bromide) (Lorenzo et al. 2020) and the second one, injecting along with the tracer, a biodegradable nonionic surfactant, Emulse® (E3) (Santos et al. 2019). The groundwater flow from the Sardas landfill was characterized by a bromide step experiment in which a constant tap water flow rate with the tracer was injected. The concentration of Br− in groundwater samples from different monitoring wells placed around the injection one with time was determined, obtaining a transport model (the software gPROMS was used to analyze the data obtained), able to predict the concentration of different reagents in the subsoil. An additional bromide injection, varying the flow rate, was later performed. The data obtained from this test validated the proposed transport model (Lorenzo et al. 2020). The second pilot test involved injecting an aqueous solution containing the nonionic and biodegradable surfactant E3 in the Sardas alluvial layer (polluted with a DNAPL) (Santos et al. 2019). The alluvial consists of a sand gravel layer with some interbedded clay. It presents high permeability but a low hydraulic gradient between two low permeability layers (lime and marl) (Fernández et al. 2013). In this experiment, 5.28 m3 of a 13 g L−1 E3 was injected in the permeable

C. M. Domínguez et al.

layer (gravel-sand) at 14.5 m b.g.l (saturated zone) with a flow rate of 0.6 m3 h−1. Bromide (130  mg L−1) was simultaneously added as a tracer to study the transport of the injected fluids. Simultaneously with the surfactant injection (and after that), the groundwater was analyzed within a test cell of 3.5 m radius from the injection point at a depth of about 14.5 m. The COCs, chloride, bromide, and E3 concentrations were quantified during the experimental time at the injection point and three monitoring points. The surface tension and conductivity were also evaluated. 15 h after the surfactant injection, the groundwater extraction began using the same well and depth. Extra tap water injections (extracting groundwater simultaneously) were performed the following days to ensure that neither the surfactant nor higher pollutant concentrations remained in the groundwater due to the surfactant injection. It was observed that surfactant adsorption was negligible during the injection step but significant in the meantime, between surfactant injection and groundwater extraction (15 h). The injected fluids were considerably diluted due to the high radial dispersion. Once it reached the equilibrium time, the COCs concentration in the surfactant solution was around 850 mg L−1, in accordance with the groundwater moderate contamination in the test cell (≈1230 mg kg−1). The addition of the surfactant greatly enhanced the extraction of the dense phase from the altered marl layer. In addition, it was found that there was no mobilization of surfactant from the capture zone. Thus, the off-site migration of contaminants due to the increased solubility achieved with E3 was discarded (Santos et al. 2019).

4.2 Surfactant-In Situ Chemical Oxidation (S-ISCO) The treatment of the residual DNAPL located in the subsoil of the Bailín landfill was carried out using anionic (SDS) and nonionic (E3, T80, and TS80) surfactants and PS activated by alkali (S-ISCO) (García-Cervilla et al. 2021a). Considering that the stability of both species (oxidant and surfactant) is a critical aspect of the effectiveness of S-ISCO processes, the nonproductive consumption of PS in the occurrence of surfactants was investigated (batch experiments, room temperature 864 h), varying the NaOH:PS molar ratio (1–2) and the surfactants (0–12 g L−1) and PS (84–42 mmol L−1) concentrations. The conversion of PS with SDS was negligible under the conditions used. In contrast, in the presence of the nonionic surfactants, its consumption ranged between 70 and 80% (360 h). The most stable surfactants that maintained a higher solubilization capacity after oxidation with PS were SDS and E3, selected

Removal of Organochlorine Pesticides from Soil and Water

for S-ISCO experiments. The addition of surfactants led to a substantial decrease in the reaction times needed to remove the DNAPL (compared to an experiment without surfactants). At the same reaction time (360 h), the pollutant conversion achieved when E3 was simultaneously added with the oxidant was around three times higher than the obtained with SDS (García-Cervilla et al. 2021a). Taking into account the hopeful results obtained with E3, this surfactant was selected to be studied for the treatment of DNAPL-polluted soil in a more practical way, performing the experiments in columns (Garcia-Cervilla et al. 2022a), conditions in which S-ISCO works are very scarce. The polluted soil was loaded in a column, and surfactant, oxidant, and NaOH were contacted with the soil using an aqueous/soil ratio of 0.2 L kg−1. The addition of surfactant increased the reduction of COCs from 40% (without E3) to 65–90% of conversion. Working with an excess of surfactant was counterproductive since it hinders COCs oxidation and increases the unproductive consumption of PS. The optimal value of E3 in solution was around 2 g L−1 (GarciaCervilla et al. 2022a). Some field-scale tests are being carried out in the Bailín landfill to implement the technology shortly. This system (E3-PS-NaOH) was also applied to treat simulated DNAPL-affected groundwater (Garcia-Cervilla et al. 2022b). The DNAPL was prepared using commercial pollutants (CB, 1,2-DCB, 1,2,3-TCB, 1,2,4-TCB, 1,2,3,4TeCB, and 1,2,3,5-TeCB). It was determined that the higher the surfactant concentration, the lower the PS consumed due to the formation of more complex micelle structures, which hinders their oxidation. The oxidation of solubilized COCs was also decreased when using high surfactant concentrations (chlorobenzenes degradation was insignificant with E3 concentrations above 2.5 g L−1). Finally, it was found that working with a surfactant and oxidant concentration of 1 g L−1 and 168 mM significantly decreased the time required to abate a mass of DNAPL, compared with the process without surfactant (Garcia-Cervilla et al. 2022b).

4.3 In Situ Chemical Oxidation (ISCO) When most residual DNAPL has been removed, the polluted groundwater plume and the COCs adsorbed in the soil can be eliminated by injecting oxidants and activators in the subsoil, as proposed in Fig. 6. The alkaline (NaOH) activation of persulfate was tested to eliminate a plume of HCHs and chlorobenzenes in Sardas landfill groundwater (Santos et al. 2018b). The effect of the main operating conditions, PS concentration (10–48 g L−1), and NaOH:PS molar ratio (2 and 4), on COCs

257

degradation was batch-wise studied. At these primary conditions (pH ≥ 12, maintained for the whole reaction time), HCH isomers were rapidly hydrodechlorinated to trichlorobenzenes (the isomer generated in the highest proportion was 1,2,4 TCB). These compounds (TCBs), along with CB, DCBs, and TetraCBs, were further oxidized by hydroxyl radicals. The proposed kinetic model adequately predicted COCs concentration in solution with reaction time. It follows first-order kinetics for pollutants and oxidant concentration and zero-order for alkali concentration. The complete degradation of COCs was achieved after 15 days of treatment (chlorinated or aromatic byproducts were not detected). The high stability of PS in the subsurface makes the proposed technology adequate for in situ remediation processes. In this sense, it is necessary to consider that the flow rate conditions the kinetics in the aquifer, which limits the yield or requires the application of several oxidation cycles. The alkaline activation of PS was also applied to treat a subsoil contaminated with chlorinated compounds from DNAPL adsorbed on the soil surface (García-Cervilla et al. 2020a). The subsoil treated was sieved into two particle sizes, F 400 gH2O2 kg soil−1) led to a high hydrogen peroxide unproductive consumption (XH2O2 ≈ 100%, 24 h) and catalyst precipitation (Dominguez et al. 2021b). Thus, applying the Fenton process to treat superficial polluted soils from Sardas and Bailín landfills requires further research, considering the use of hydrogen peroxide stabilizing agents and chelating agents able to maintain the catalyst in solution at neutral pH (Checa-Fernandez et al. 2021a).

5.1.2 Persulfate-Based Processes Superficial soils coming from different points of Bailín landfill (with different concentrations of α-HCH and β-HCH isomers) were treated by persulfate-based processes, viz., thermal activation of persulfate, alkaline activation of persulfate, alkaline activation of persulfate intensified by temperature and by US (Dominguez et al. 2021a, b; Checa-Fernández et al. 2021c, d, 2022). The low HCH-isomers water solubility, high COCs refractoriness toward oxidation, and particulate matter presence limited the efficiency of the first treatment (thermal PS). At 40 °C, only 50% of HCHs conversion was achieved (CPS = 40  g L−1, VL/Wsoil =  2, 25  days) (Dominguez et al. 2021b). Optimization of the primary process variables (reaction temperature, from 35 to 55 °C, and initial PS concentration, from 10 to 80 g L−1) was carried out to decrease reaction times (Dominguez et al. 2021a). A reaction temperature increase is associated with increased HCHs oxidation and dechlorination rates and lower production of chlorinated byproducts. PS concentration also plays a crucial role in pollutant degradation. When working at 55 °C and 80 g L−1 of PS, HCHs (α-HCH = 254 mg kg−1 and β-HCH = 99 mg kg−1) conversion of 83% was accomplished after 9 days. The chlorine balance was wholly accomplished, and no chlorinated byproducts were detected (Dominguez et al. 2021a). The alkaline activation of persulfate led to promising results for the remediation of HCH-contaminated sediments, although reaction temperatures above the ambient were required (Dominguez et al. 2021b). The primary pollutants of the sediments were α-HCH and β-HCH. At pH above 12, HCH isomers were dehydrochlorinated to TCBs (α-HCH hydrolysis was almost instantaneous, whereas β-HCH was slowly hydrolyzed). TCBs were subsequently attacked by the hydroxyl radicals generated (the principal oxidizing agent in this system). The limiting step of the process (β-HCH hydrolysis) was favored with the reaction temperature increase (Dominguez et al. 2021b). The

Batch (VL/ WS = 2, 10 g of soil)

• Xα-HCH = 100%, XβHCH = 50%, XCOCs = 49%, XPS = 15% (14 days) • At pH > 12, HCHs were dehydrochlorinated to TCBs • TCBs have higher solubility in water and are easily oxidable by the hydroxyl radicals than the parents’ pollutants (HCHs) • The hydrolysis of β-HCH to TCBs is the limiting step • Xα-HCH = 100%, XβHCH = 93%, XCOCs = 95%, XPS = 30% (14 days) • Temperature plays a crucial role in the process as the hydrolysis of β-HCH (limiting step) was favored by its increase

CPS = 40 g L−1 pH > 12 CNaOH = 13.5 g L−1 NaOH:PS (mol:mol) = 2:1 T = 40 °C 100 rpm •T • NaOH addition

Oxidation (PS activated by alkali and intensified by T)

(continued)

• T = 20 °C: XCOCs = 8%, XPS = 8% (14 days) • T = 40 °C: XCOCs = 46%, XPS = 13% (14 days) • The thermal activation of PS at the conditions tested (20 and 40 °C) was inefficient in the HCHs oxidation due to the low solubility of these compounds in water and their refractoriness toward oxidation

CPS = 40 g L−1 T = 20–40 °C Natural pH 100 rpm

References

• CH2O2 = 12 g Dominguez et al. XCOCs = 2%, XH2O2 = 100% (2021b) Fe/Fe0 = 0 (72 h) • CH2O2 = 200 g L−1: XCOCs = 40%, XH2O2 = 100% Fe/Fe0 = 0 at (72 h) • The high carbonate content of the soil led to excessive H2O2 (oxidant) consumption and Fe (catalyst) precipitation

L−1:

Major findings/conclusions

CH2O2 = 12–200 g Fe = 0.5 g L−1 T = 22 °C Natural pH 100 rpm

L−1

CPS = 40 g L−1 pH > 12 CNaOH = 13.5 g L−1 NaOH:PS (mol:mol) = 2:1 T = 20 °C 100 rpm

• CH2O2

Variables studied Experimental conditions

• NaOH addition

β-HCH = 35 mg kg−1

α-HCH = 120 mg kg−1

Oxidation (PS activated by alkali)

Superficial soil (Bailin’s landfill) Øp = 0.2–0.7  mm

Pollutant

Reaction system

•T

Application of different chemical oxidation treatments to the remediation of superficial soils polluted with technical HCH

Oxidation (Fenton process)

Sample type

Oxidation (PS activated by temperature)

Focus of study

Chemical treatment

Table 4  Research studies on on-site treatments of superficial soils

Removal of Organochlorine Pesticides from Soil and Water 259

Oxidation (PS activated by alkali and intensified by T)

β-HCH = 99 mg kg−1

Pollutant

α-HCH = 254 mg kg−1 β-HCH = 99 mg kg−1

Reaction system

Superficial soil Study the effect Batch (VL/ (Bailin’s landfill) WS = 2, 15 g of of the operating Øp = 0.02–0.25  mm soil) conditions of the alkaline activation of PS intensified by temperature for the remediation of superficial soils polluted with technical-HCH

Sample type

Oxidation (PS actiEvaluation of the Superficial soil Batch (VL/ (Bailin’s landfill) WS = 2, 15 g of vated by temperature) effect of temperature and initial Øp = 0.02–0.25  mm soil) oxidant concentration on remediation of superficial soils polluted with technical HCH by thermally activated PS

Focus of study α-HCH = 254 mg kg−1

Chemical treatment

Table 4  (continued)

• Reagents’ addition order •T • VL/WS • CPS • Stirring rate

• CPS •T

Addition of reagents: sim./seq T = 40–60 °C VL/WS = 1–2 CPS = 20–60 g L−1 CNaOH = 13.5 g L−1 (NaOH:PS (mol:mol) = 2:1) Stirring rate = 10–100  rpm

CPS = 10–80 g T = 35–55 °C Natural pH, 100 rpm

L−1

Variables studied Experimental conditions

References

(continued)

Checa-Fernández • Reagent’s addition order et al. (2021d) did not affect the process efficiency • Raising T or CPS accelerates the β-HCH hydrolysis (limiting step) • Increasing the VL/WS ratio accelerated XCOCs conversion • No significant differences in XCOCs were obtained when increasing the stirring rate from 10 to 50 rpm. However, higher XCOCs was achieved by increasing the stirring rate up to 100 rpm • Xα-HCH = 100%, XβHCH = 81%, Cl/Cl0 = 94% and XPS = 29% (Addition of reagents: sim., T = 50 °C, VL/WS = 2, CPS = 40  g L−1, pH > 12, NaOH:PS (mol:mol) = 2:1, 100 rpm, 3 days) • Aqueous solution could be reused in a new batch (separation of aqueous and soil phases: a rapid sedimentation step)

• The increase in T and initial Dominguez et al. (2021a) CPS increases the production of sulfate radicals, and therefore, the XHCHs and dechlorination degree • PS decomposition follows first-order kinetic, and its stability increases in the presence of soil • XCOCs = 83% (T = 55 °C, CPS = 80 g L−1, 9 days) with no chlorinated intermediate compounds • Soil physicochemical characteristics were unaltered after the application of thermal activation of PS, facilitating a subsequent bioremediation treatment

Major findings/conclusions

260 C. M. Domínguez et al.

(a) Surfactants increase the Checa-Fernandez COCs solubility (Csurf = 10  g et al. (2021b) L−1); SDS and E3 solubilize a higher COCs proportion at pH > 12, and T80 at neutral pH (b) High stability of SDS (XPS ≈ 25% at pH = 7 and pH > 12, 5 h); low stability of T80 and E3 at alkaline conditions (XPS  75% at pH > 12, 5  h). T80 is recommended when the SSW is followed by a remediation treatment at neutral pH, and SDS at basic pH (c) SDS (pH > 12): XCOCs = 18% (5 h) T80 (pH = 7): XCOCs = 76% (5 h)

(a) Soil washing: Csurf = 1–10 g L−1, CNaOH = 0–13.5 g L−1 24 h (b) Unproductive consumption of PS: Csurf = 10 g L−1 CPS = 40 g L−1, CNaOH = 0–13.5 g L−1 T = 60 °C (c) COCs oxidation CPS = 40 g L−1 T = 60 °C

VL/WS  liquid/soil phase ratio (VL in ml and WS in g), PS persulfate, Øp particle diameter, COC chlorinated organic compound, Cl/Cl0 Dechlorination degree, US ultrasounds, sim. simultaneous, seq. sequential, surf surfactant, E3 E-Mulse® 3, T80 Tween®80, SDS sodium dodecyl sulfate, SFS surfactant flushing solution

• Surfactant type (SDS, T80, E3) • Csurf • pH

α-HCH = 254 mg kg−1 β-HCH = 99 mg kg−1

Surfactant soil washing (SSW) and subsequent oxidation (PS-based treatment)

Study the use Superficial soil Batch (VL/ of surfactants (Bailin’s landfill) WS = 2, 15 g of for soil washing Øp = 0.02–0.25  mm soil) at neutral and alkaline conditions and subsequent PS-based oxidations treatments for the remediation of superficial soils polluted with technical-HCH

• The US application increases Checa-Fernandez the temperature and promotes et al. (2021c, 2022) the pollutants desorption from soil, increasing the XHCHs • The higher the US power and the initial CPS, the higher the XHCHs and the dechlorination degree • XCOCs = 94%, Cl/Cl0 = 74% and XPS = 25% (165 W, CPS = 60 g L−1, pH > 12, NaOH:PS (mol:mol) = 2:1, VL/WS = 2, 3 h) • The oxidation process did not increase the ecotoxicity of the soil, facilitating a subsequent remediation treatment

US power = 0–245 W CPS = 10–60 g L−1 pH > 12 CNaOH = 13.5 g L−1 NaOH:PS (mol:mol) = 2:1 VL/WS = 2

• US application • US power • CPS

β-HCH = 110 mg kg−1

Oxidation (PS actiStudy the effect of Superficial soil Batch (VL/ vated by alkali and the main operating (Bailin’s landfill) WS = 2, 15 g of Øp = 0.02–0.25  mm soil) intensified by the US) conditions of the alkaline activation of PS intensified by the US for the remediation of superficial soils polluted with technical-HCH

References

Major findings/conclusions

Reaction system

Variables studied Experimental conditions

Sample type α-HCH = 282 mg kg−1

Focus of study

Pollutant

Chemical treatment

Table 4  (continued)

Removal of Organochlorine Pesticides from Soil and Water 261

262

influence of reagents (NaOH and PS) addition order, temperature (40–60 °C), PS concentration (20–60 g L−1), liquid/soil mass ratio (VL/WS = 1 and 2), and stirring rate (10–100 rpm) on COCs degradation and dechlorination was explored (Checa-Fernández et al. 2021d). The process was not affected by the reagents addition order. Increasing reaction temperature and oxidant concentration accelerates β-HCH hydrolysis rate (controlling step) and TCBs oxidation rate, whereas increasing liquid/soil mass ratio and stirring rate was also beneficial. The complete degradation of α-HCH and 81% of β-HCH, with 94% of dechlorination, were achieved in only 3 days (pH > 12, simultaneous reagents addition, 50 °C, PS = 40 g L−1, VL/WS = 2, NaOH/ PS = 2 and 100 rpm). Under these conditions, the oxidant consumption was relatively low (XPS = 29%), allowing the aqueous solution to be recycled in a new soil remediation batch. Moreover, aqueous and soil phases were separated under alkaline conditions by a rapid sedimentation step (Checa-Fernández et al. 2021d). The intensification of the alkaline activation of persulfate by ultrasounds (US) has been investigated for remediating HCHs-polluted sediments (α-HCH and β-HCH concentration = 282 and 110 mg kg−1, respectively) (Checa-Fernandez et al. 2021c, 2022). The application of US improves pollutant desorption and generates radical species from PS activation (Eq. 7). Moreover, US energy increases the system temperature, favoring the kinetics of the remediation process. The influence of US power (0–245 W) and PS concentrations (10–60 g L−1) was evaluated. A COCs conversion above 94% and a dechlorination degree of 74% were obtained in 3 h (VL/Wsoil = 2, CPS = 60 g L−1, NaOH:PS = 2:1, 165 W). Furthermore, ecotoxicity measurements (Microtox® bioassay) of the initial and treated soil demonstrated no potential toxicity of the oxidation process, facilitating a subsequent remediation treatment.

5.2 Surfactants Soil Washing and Oxidation of the Resulting Emulsion The low aqueous solubility of pollutants of concern can limit the efficiency of oxidation processes, mainly in the aqueous phase (Wang et al. 2017). In this context, the use of surfactants has dramatically increased in the last few years. As previously shown, these substances raise the wetting, solubilization, and emulsification of organic pollutants, such as HCHs. Thus, the on-site washing of superficial soils/sediments with surfactant solutions was highlighted as an exciting alternative for sites contaminated with HCHs. The pollutants are transferred from the soil to the surfactant-aqueous phase, and additional treatments are

C. M. Domínguez et al.

required for their destruction. Thus, the washing solution (with high pollutant concentration) should be treated with suitable technologies, such as persulfate-based oxidation processes. The success of the surfactant application followed by a PS post-treatment highly depends on the contaminant/surfactant/oxidant system. Firstly, the surfactant should exhibit high pollutant solubility capacity. Its adsorption onto the soil should also be considered. Furthermore, the oxidant must be efficient in the pollutant’s abatement and stable when in contact with the surfactants. The remediation of lindane spiked soil (100 mg kg−1) was evaluated using an anionic surfactant (SDS) followed by electrolysis using BDD and stainless steel electrodes (Muñoz-Morales et al. 2017), giving rise to complete pollutant elimination. The SDS/soil ratio was determinant in the efficiency of the soil washing step and the performance of the subsequent electrooxidation process (15 Ah L−1). The soil-washing solutions were effectively mineralized by electrolysis: lindane was rapidly oxidized, and no intermediates were identified at the final reaction time. The surfactant (SDS) was slowly degraded under these conditions, releasing sulfate ions into the solution. At the end of the treatment, more than 70% of this compound was recovered, allowing its reuse for further treatments (Muñoz-Morales et al. 2017). Three commercial surfactants (also used for the remediation of the landfills subsoils), an anionic surfactant, SDS, and two nonionic surfactants, T80 and E3, have been tested for the HCHs-superficial soil (α-HCH and β-HCH = 254 and 99 mg kg−1, respectively) washing at neutral and basic pH (Checa-Fernandez Alicia et al. 2021). The partition coefficient (Kd) determined the surfactant capacity, representing the mass ratio of COCs between the soil and the aqueous phases at equilibrium conditions. The lower the Kd, the greater the capacity of the surfactants to solubilize the pollutants. In the absence of surfactants, the Kd decreases at alkaline pH, which is explained by attending to the HCH hydrolysis to TCBs, compounds much more soluble than the parent ones. The addition of surfactants (10 g L−1, VL/ Wsoil = 2) increases the mass of pollutants solubilized in the aqueous phase (decreasing the Kd values) for the three surfactants tested at neutral conditions and for SDS and E3 at alkaline ones. The nonionic surfactant T80 showed low solubilization capacity due to its low stability at pH above 12 (Checa-Fernandez Alicia et al. 2021). The unproductive consumption of PS increased in the presence of surfactants (PS = 40  g L−1, surfactant = 10  g L−1, 60 °C). The ionic surfactant, SDS, led to low PS consumption at neutral and alkaline pH and T80 and E3 at neutral pH, in which sulfate radicals are the main oxidant

Removal of Organochlorine Pesticides from Soil and Water

species. However, under alkaline conditions, the process in which hydroxyl radicals are predominant, the PS consumption associated with the nonionic surfactants was excessive, ruling out this use at these conditions. Thus, under alkaline conditions, the linear alkyl chain of the anionic surfactant is more refractory to radical attack than the polyethoxylated chains of nonionic surfactants. Considering the surfactant capacity and the persulfate unproductive consumption, the soil washing solutions obtained with T80 at circumneutral pH and SDS at basic pH were treated with PS (40 g L−1, 60 °C, 5 h), obtaining an insufficient COCs conversion in the first case and 80% of COCs degradation in the second one. Therefore, although further research is needed, SDS is highlighted as an encouraging alternative for remediating soils contaminated with HCHs (soil washing + oxidation by the alkaline activation of PS) (Checa-Fernandez Alicia et al. 2021).

6 Future Perspectives The final step of the treatment train for soil remediation would be its biotreatment (Fig. 6). Bioremediation is a process that uses microorganisms, fungi, yeast, plants, or plant enzymes to bring back an environment negatively modified by contaminants to its natural condition. Contaminants are usually degraded to obtain energy for living organisms. This process could be directly applied to soils with a low concentration of COCs or to contaminated soils after the chemical treatment. Nevertheless, soil characterization tests do not discriminate between compounds available to biological systems and inert, complexed, or unavailable compounds (Corbisier et al. 1996). Therefore, determining the concentration of pollutants in the soil is not enough to predict its bioremediation. Moreover, applying oxidants and surfactants to the soil (superficial and at the subsurface) can affect its biological activity and, therefore, the efficiency of future bioremediation treatments. Despite the importance of this aspect, very little information in this regard has been found in the scientific literature, and therefore this topic requires deeper investigation. This issue is exciting when the alkaline activation of persulfate (the process in which high alkaline pHs are required) is accomplished and when surfactants (SEAR) or surfactants and oxidants (S-ISCO) are simultaneously injected into the subsoil. In this scenario, several bioassays, such as the cladocera Daphnia magna and the marine bacteria Vibrio fischeri, are valuable tools for assessing the bioavailable fraction of soil pollutants and determining their acute toxicity. Thus, the acute toxicity of polluted soils can be accomplished using the Microtox® bioassay. Firstly, to validate this method for

263

determining the acute toxicity of soils from the landfills, samples with different degrees of contamination (in terms of composition and concentration) and different mineralogy (gravels, fines) should be measured. Measurements of the solid phase (polluted soils) and the aqueous phase (water in contact with the soil phase to determine the toxicity of the leachate) will be carried out. In addition, due to the high hydrophobicity of the contaminants, they will be extracted from the soil phase to an organic phase, and the toxicity of this phase will also be measured. Once the method is validated, the original contaminated soils and the soils treated with the different procedures (surfactants, activated oxidants, and surfactants combined with activated oxidants) will be investigated. The synergistic effect (positive or negative) of surfactants and oxidants on soil toxicity will be evaluated by considering the concentration of COCs in each soil sample. Researchers are developing this study from the INPROQUIMA group with interesting results. To obtain toxicity results with another trophic level, an analysis procedure equivalent to that described for Vibrio fischeri should be carried out with Daphnia magna. Finally, a study of soil biological activity before and after the chemical treatments should be performed. In this sense, biological functional diversity and enzyme activity tests can be used to analyze the effect of chemical treatment on soil microorganisms. The remediation of superficial polluted soils from landfills with a relatively low level of contamination (ΣHCHs ≈ 100 mg kg−1) using organic amendments (horse droppings) has been carried out, obtaining auspicious results in just two months of treatment (unpublished results). The possible bioremediation of soils from the polluted site contaminated with HCHs showing different levels of contamination and using different types of organic amendments is being studied, as well as the evaluation of the soils obtained after the chemical treatments. Finally, the studies carried out in the laboratory on Sardas leachates indicate that biostimulation is sufficient to treat these leachates both aerobically and anaerobically, with yields >99% in less than 15 days. On the other hand, the production of bacterial biomass with and without carbon sources apart from contaminants and the versatility of bacterial consortia from different environmental matrices (soils, sludge, sediments, soils, root systems) to evaluate the diversity of carbon sources used and tolerance levels using different concentrations of toxic soup (solubilizing DNAPL), are being characterized. So far, the results indicate the feasibility of autochthonous consortiums to degrade all chlorinated compounds at high concentrations. In addition, in soils with particulate contamination, the concentration of the contaminants is not a limiting factor since bioavailability is not significantly increased.

264 Acknowledgements  The authors acknowledge the financial support from the Regional Government of Madrid through the CARESOIL project (S2018/EMT-4317), the Spanish Ministry of Science (project PID2019-105934RB-I00), the EU LIFE Program (LIFE17 ENV/ ES/000260) and SARGA, a public company of the Government of Aragon (project ref. 5507001-182 funded). The authors also thank the Department of Climate Change and Environmental Education, Government of Aragon, EMGRISA, M. Oturan, and N. Oturan (Université Paris-Est, Marne-la-Vallée Cedex 2, France) for their support.

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Recent Patents and Modern Industrial Devices for Clean Water Aiman Eid Al-Rawajfeh, Ghada Al Bazedi, Muhammad Kashif Shahid, Hosam Al-Itawi and Jun Wei Lim

Abstract

Keywords

This chapter offers an overview of the latest advancements in the field of clean water production and monitoring. It summarizes a selection of recent, important patents in the field and discusses the technological readiness level of the various patented systems. These patents demonstrate the ongoing efforts to develop innovative technologies and methods for water treatment applications, highlighting the importance of staying up to date with the latest advancements in the field. The chapter concludes by emphasizing the need for continued research and development in the field of clean water, to ensure access to clean and safe water for all.

Membrane water operation · Solar desalination · Heat exchangers · Nanomaterials · Composite membranes · Electrochemical deionization · Microbial fuel cell · Vacuum distillation

A. E. Al-Rawajfeh (*) · H. Al-Itawi  Tafila Technical University, P.O. Box 179, Tafila 66110, Jordan e-mail: [email protected] G. Al Bazedi  Center for Applied Research On the Environment and Sustainability (CARES), School of Science and Engineering, The American University, New Cairo, AUC Avenue, P.O. Box: 74, Cairo 11835, Egypt Chemical Engineering & Pilot Plant Department, Engineering Research Division, National Research Center, Cairo Post Code, 33 El-Bohouth St, Dokki 12311, Egypt M. K. Shahid  Research Institute of Environment & Biosystem, Chungnam National University, Yuseong-Gu, Daejeon 34134, Republic of Korea J. W. Lim  HICoE-Centre for Biofuel and Biochemical Research, Institute of Self-Sustainable Building, Department of Fundamental and Applied Sciences, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia Department of Biotechnology, Saveetha School of Engineering, Saveetha Institute of Medical and Technical Sciences, Chennai 602105, India

1 Introduction Clean drinking water is in short supply globally, and there’s also a lack of water for industrial, agricultural, and irrigation needs. Prolonged drought and persistent water scarcity have hindered economic growth in various regions of the world and may eventually lead to the departure of some urban centers (du Plessis 2023; Rusca et al. 2023). There is an abundance of pure water in other regions of the world, but it is polluted with chemicals and minerals from industrial sources and agricultural methods (Flörke et al. 2018; Mi et al. 2019; Tzanakakis et al. 2020). Innovation may help to reduce water-related hazards and enhance the delivery of water services that are critical to our well-being and long-term development (Shahid et al. 2020; Tan and Zou 2023). Water-related innovation emerges from a diverse set of countries with varying degrees of ambition. They spread at various world sizes (Hyvärinen et al. 2020). This research utilizes patent data to record trends in the innovation of technologies to increase water security, concentrating on where ideas are created, where they may be commercialized, and which subsectors they originate. New technologies can help communities profit from water’s many productive applications, preserve ecosystem services, and manage water-related dangers. Water storage, conservation, and other beneficial applications may be completely realized via innovation. It can aid in the treatment and recycling of wastewater, as well as the prevention of ecosystem contamination. It can help reduce flood threats.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 K. Jlassi et al. (eds.), Clean Water: Next Generation Technologies, Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-031-48228-1_17

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Water security is improved through technological progress in various domains. Evaluating both present and future possibilities in developing new technologies, treatment methods, and equipment for desalination and wastewater treatment is critical for the advancement of the water treatment industry (Shahid et al. 2021; Wijewardane and Ghaffour 2023). With the increasing demand for clean water and sustainable water management practices, there is a growing need for innovative technologies and methods that can improve the efficiency and effectiveness of water treatment processes (Dayarathne et al. 2023; Javed et al. 2019; Shahid and Choi 2022). Recently, there have been noteworthy advancements in the development of new technologies and methods for water treatment. For example, advanced functional materials and membrane filtration, including reverse osmosis and nanofiltration, have become a widely used technology for water desalination and purification (El Fadil et al. 2023; Khan et al. 2022). Additionally, the use of smart sensors and instrumentation has revolutionized the monitoring and control of water treatment processes (Garrido-Momparler and Peris 2022; Murugan et al. 2023). These technologies enable real-time monitoring of water quality parameters, allowing for prompt response to changes in water quality and optimizing treatment processes. Looking to the future, there is a rising focus on the development of sustainable and energy-efficient water treatment technologies. For example, the use of renewable energy sources, such as solar and wind, to power treatment processes is becoming more prevalent (Shahid et al. 2023). Additionally, the development of energy recovery technologies, such as pressure exchange and turbine systems, is gaining momentum, as it allows for the recovery of energy from high-pressure wastewater streams (Gholamian et al. 2023; Guzmán-Avalos et al. 2023). Overall, the prospects for advancing new technologies, treatment methods, instruments, and equipment for desalination applications are positive, driven by the increasing demand for clean water and sustainable water management practices. Fig. 1  Emerging desalination technologies

In conclusion, this chapter provides a comprehensive overview of recent patents and innovations in water treatment systems, including advancements in treatment methods, equipment, and instruments that have the potential to significantly improve the efficiency and effectiveness of water and wastewater treatment processes.

2 Desalination Technology Patent Activity A list of keywords is created for both technical classifications and general desalination systems, encompassing additional emerging innovations not specifically recognized by experts. The distinctions between categories are unclear, and there is data redundancy that extends across all of them. Many of these classifications and arrangements resulted in patents that were not just related to the technical target areas, but also patents that were not. Water-related technologies identified in the article fall into five major categories: • • • • •

Desalination systems Membrane technology Nanotechnology in water treatment Solar desalination systems New trends in desalination and water treatment

A comprehensive review of global patents and licenses was conducted to ascertain whether any category of desalination technology is likely to become more widespread. In the year 2020, two particular types of technology exhibited notably higher levels of patent activity compared to the rest. The initial one involves electrochemical processes, as shown in Fig. 1, which have ten patents, while the second pertains to operational efficiency solutions, boasting nine patents. These two fields exhibited over twice the number of patents compared to the following most active technological categories (BlueTech Research, Patent Watch 2020) (Jong et al. 2021).

Emerging Desalination Technologies Forward Osmosis Electro-Chemical (ED.EDR,EDI) Membrane Distillation

Recent Patents and Modern Industrial Devices for Clean Water Fig. 2  Vendor count of desalination technologies worldwide

The development of desalination technologies should not only be innovative but also set themselves apart from current methods. Emerging technologies are evaluated based on their ability to enhance efficiency, manage pollutant concentration, or introduce unique business models. As shown in Fig. 2, the vendor count of each technology distribution. It is clear that the potential for a technology to be disruptive enough to establish a market presence and compete with conventional solutions is an essential consideration (Jong et al. 2021).

3 Desalination Systems Population growth and fast industrialization have placed a high demand on clean water production. Currently, reverse osmosis is the dominating technology for producing drinking water (RO). However, the typical RO process has a maximum recovery rate of roughly 35–50% since it is limited by the maximum salinity of the feed (e.g., > 70 g/L) and practical considerations including membrane’s mechanical strength environmental and economic apprehensions (Bartholomew et al. 2017; Liang et al. 2021). The salty feed becomes more concentrated as the water recovery rises. As a result, the RO process must use additional energy to counteract the osmotic pressure of the concentrated saline water. Furthermore, the treatment of RO concentrate comes with a substantial cost. WO2022159175 (2022), the current application is oriented at systems and methods for configuring desalination system components to ensure high permeate recovery rates while maintaining a small footprint for operation in point-ofuse applications. The reconfiguration and/or deletion of one or more components of these high-pressure systems can considerably lower the overall footprint of the system, allowing for point-of-use application operability without losing the recovery ratio of a traditional system (Wei et al. 2022).

269 Reverse Osmosis Thermal Desalination Emerging Technologies Other

WO2022151608 (2022), Seawater desalination highpressure pump and turbine-type energy recovery integrated machine is widely used in drilling platforms, and other fields, with the characteristics of high efficiency, convenience, and energy saving. The turbine-type seawater integrated machine utilizes the energy of this part of highpressure seawater, uses a turbine to recover this portion of the remaining energy, and directly drives the high-pressure pump to run. The turbine unit recovers the high-pressure energy of seawater as the motor of the device. The highpressure pump unit at the other end is driven by the coaxial to work and run (Zhang et al. 2022). In CN211871451 (2020), the utility model is related to the technological sector of seawater desalination equipment and discloses a low-temperature multi-effect seawater desalination device (Peiyin et al. 2021). EP4028365 (2020) pertains to a technique for desalinating a first fluid (F1) using a second fluid (F2), with the first fluid (F1) having a lower salinity compared to the second fluid (F2). Both fluids, ideally water, were subjected to a pressure-retarded osmosis (PRO) step and an RO step. The method requires feeding both fluids into a PRO and subsequently introducing the F2 into the PRO under pressure. The F1 is then pressurized by engaging in a pressure exchange with the pressurized F2 that exits the PRO unit. After that, the pressurized F1 is fed into an RO unit to recover a third fluid (F3) having a lower salinity than the F1 (Fourno 2022). The system is designed to minimize energy consumption during the water desalination process, resulting in a reduction in both the cost of the desalination system and the cost of the overall process. A saline solution is fed to a membrane unit at high pressure, for example, between 650 and 950 Psi, in a conventional desalination system utilizing a reverse osmosis membrane (4500 to 6500 kPa). The volume of the solution is lowered and the salinity is raised after passing through the saline side of the membrane unit, with a part of the

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freshwater removed through the membrane. The pressure in this exhaust liquid or concentrate remains high. A feed pump pressurizes the saline solution used to feed the membrane unit. In certain systems, the feed pump has a single cylinder and is controlled by a lever. In bigger systems, the feed pump may be operated mechanically, for as by an electric motor. US20200166025 (2020), the current invention pertains to pumps, and more specifically to pumps for membrane filtering systems such as desalination systems, as well as systems that include the pumps. The invention provides a pump or a desalination system that overcomes the aforementioned shortcomings or at the very least provides the public or business with a beneficial alternative (DENT 2022). The process of freeze desalination is becoming increasingly popular in specialized areas, particularly in cases where more cost-effective or unused energy sources, such as solar cooling, thermoacoustic refrigerators powered by waste heat, and cold energy derived from liquefied natural gas, are accessible (Wijewardane and Ghaffour 2023). The development and advancement of heat and solardriven cooling technologies have contributed significantly to freeze desalination. Recently, Janajreh et al. provided a comprehensive overview of various freeze desalination configurations, while also detailing the advantages and disadvantages of each approach (Janajreh et al. 2023). The article also discusses recent experimental research aimed at investigating the underlying physics of the technology, as well as reviewing the most up-to-date high-fidelity numerical modeling techniques that simulate the freezing of brine and the resulting salt diffusion away from the crystal lattice. These numerical models are made possible by recent advancements in computational power and the integration of multiphysics techniques. Najim evaluated the progress made in freeze desalination techniques, including independent and hybrid methods, which work with or without using the energy discharged during liquefied natural gas regasification (Najim 2022). Additionally, the review explored potential future research and development areas that could facilitate the commercial viability of freeze desalination technology. US20210139346A1 described a method for desalinating saltwater using a single-stage freezing process, in which a cooled intermediate-cold liquid (ICL) was used (Shabgard et al. 2021). The method involved introducing the feed brine and ICL to a crystallization tank, allowing them to form a slurry of ice, brine, and ICL, and then separating the ice, brine, and ICL. The separated ICL was returned to the source of the cooled ICL, while the brine was passed back to the crystallization tank. Finally, the separated ice was melted to obtain desalinated water. The patent application US20230014345A1 described an innovative apparatus, system, and method for desalinating

A. E. Al-Rawajfeh et al.

water (Katz 2023). The apparatus comprised an outer housing with at least one inlet and two outlets, through which contaminated water flowed into the apparatus and purified vapor exited through a first outlet, while contaminated water with a portion removed as vapor exited through a second outlet. An inner tube with a plurality of holes was also located inside the outer housing and was connected to the first outlet. A finned tube heat exchanger was situated within the outer housing, and a heat energy source was connected to the heat exchanger, causing a portion of the contaminated water inside the heat exchanger to form vapor. The vapor flowed through the inner tube and exited the thermal desalination apparatus. By creating condensation sections and separate flow paths within the heat exchanger, the need for additional equipment is eliminated, and less energy is required to produce the steam needed for traditional steam distillation processes. This leads to a reduction in both capital costs and the amount of waste energy or energy costs associated with fluid purification. US10864482B2 introduced an innovative apparatus, system, and method for purifying produced water from a wellbore using energy (Katz 2020). The apparatus included a wellbore with a wellhead attached, at least one energy recapture device connected to the wellhead, and at least one RO membrane connected to the pressure recapture device. The energy recapture device captured fluid pressure from the production fluids, including produced water, while the RO membrane used a portion of the fluid pressure from the energy recapture device to remove contaminants from the produced water and create purified water. The method involved utilizing the apparatus, while the system comprised a control panel that operated the energy recapture device and the RO membrane in a coordinated manner.

4 Membrane Technology US20220152558 (2020) introduced a new method for the fabrication of polymer-based membranes (Baig et al. 2022). The method involves preparing a casting solution containing various components, including titanium dioxide nanoparticles, a solvent made from polyvinylidene fluoride, and a modifying agent made from polyvinylpyrrolidone. This solution is dispersed to form a first element, and then a plurality of active sites is generated on its surface. Finally, a polymer-based membrane is formed by exposing the surface of the first element to a fluorosilane composition, resulting in the creation of a fluorosilane layer on the surface. The fluorosilane composition includes a silane compound that has at least one alkyl substituent featuring between 9 and 21 fluorine atoms. The membranes were fabricated to control water flux, salt rejection, and resist fouling, and were useful in various technologies including RO,

Recent Patents and Modern Industrial Devices for Clean Water

FO, NF, MF, and UF. They were durable and cost-effective due to the simple fabrication method and constituent materials. These methods produced super-hydrophobic and oleophobic membranes. The membranes had many applications such as membrane distillation, treating petroleum-produced water, oily wastewater, highly saline and fouling water, contaminated groundwater, and brackish water. They were advantageous in applications requiring water and/or oilrepellent surfaces, and their cost-effectiveness made them a practical choice for many uses. The invention described in US20220193619 (2022) aimed to increase the water permeability of a polyamide RO membrane by managing a pleated structure of a skin layer to provide a wider surface area. This resulted in a permselective membrane with exceptional water permeability. The invention used a support membrane with a desalination capacity ranging from 1 to 20% under a pressure of 0.1 MPa, accompanied by a permeation flux of 20 L/(m2.h) or above. This allowed for the creation of a permselective membrane with high permeation flux and pressure resistance, independent of the support membrane’s permeation flux. The retention of a lipid membrane by the support membrane further enhanced the performance of the permselective membrane (Matsuyama et al. 2022). WO2022167951 (2022) introduced the concept of the osmotically aided reverse osmosis (OARO) process, aiming to enhance the water recovery of the RO process that had reached its operational limits. Both OARO and RO processes require robust membranes. To meet this demand, robust thin-film composite (TFC) hollow-fiber membranes with high mechanical strength were designed for utilization in both RO and OARO processes (Choong et al. 2022). The TFC hollow-fiber membranes were produced by regulating the flow rates of bore and dope fluids, as well as adjusting fiber dimensions and shape. The resulting TFC-PES hollow-fiber membranes had a pure water permeability (PWP) of roughly 25 to 30 L/(m2.h MPa) (LMH/MPa) and a salt rejection rate of approximately 97.5 to 98.8%. The newly developed membranes offer significant potential for highpressure applications, including RO, PRO, and OARO. Recent research in membrane distillation (MD) has focused on developing membranes specifically for MD applications, with the aim of improving durability and permeation flow (Francis et al. 2022; Sinha Ray et al. 2020). A number of studies have highlighted the need for higher flux MD membranes (Mohanadas et al. 2023) leading Khayet et al. (2006) to pioneer the idea of hydrophobic/hydrophilic composite membranes for MD. These membranes have been shown to meet the needs for greater flux MD membranes, and were created in a single casting stage using the phase inversion method. (Khayet et al. 2006). The process involved combining a hydrophilic base polymer with hydrophobic surface modifying macromolecules (SMMs).

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US20210001274 (2021) developed a model to guide the design of a new membrane for membrane distillation at a small trans-membrane temperature difference, even at low feed water temperatures. This resulted in the creation of a super-hydrophobic composite membrane that is both nanoporous and micro-porous. By operating at extremely low input feed temperatures, this membrane has a tendency to significantly reduce the energy needs of the MD process (Qtaishat et al. 2021). The US20230056889A1 patent application addressed two major challenges facing seawater desalination: high consumption of energy and adverse environmental impressions associated with hypersaline brine (Segawa 2023). To address these challenges, the invention utilized the principle that fluid pressure increases with depth. By relocating the reverse osmosis process to depths where the weight of the water provided the necessary pressure to drive the process, the need for high-intake pressure was eliminated, leading to a significant reduction in energy consumption. Additionally, by adjusting pumping rates, the brine stream could be prediluted to slightly above the original levels, reducing its environmental impact. The system was designed to be simple, which resulted in lower costs for building and installation. This makes seawater desalination more accessible and likely to proliferate around the world. Overall, the invention provided an innovative and sustainable solution to critical issues facing the seawater desalination industry, paving the way for a more cost-effective approach to water supply. US20220002170A1 described systems, devices, and techniques for desalinating ocean water through the utilization of gravitational force (Phatak 2022). An illustrative method for desalinating ocean water encompassed deploying a structure featuring an RO membrane attached to one end. This structure was submerged to a specific depth within a saltwater reservoir, with the depth determined by the critical pressure of activation necessary for the RO membrane to function effectively. The hydrostatic pressure at that depth compelled salt water from the reservoir to pass through the RO membrane, leading to the accumulation of freshwater within an internal cavity of the structure. This collected fresh water was subsequently accessible for external applications. Figure 3 shows a desalination system mounted on a steep sloping terrain. A composite biomimetic membrane with artificial water channels is presented in US20220347633A1 (Barboiu et al. 2022). The membrane has a biomimetic architecture consisting of nanometric supra-molecular aggregates of artificial water channels in a structure of soft material within a rigid polyamide polymer matrix. This architecture provides high water permeability while preventing the transport of cations and anions, resulting in increased transport capacity and high ionic retention. The composite biomimetic membrane with artificial water channels can be used for

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Fig. 3  A desalination setup mounted on a steep sloping terrain (Phatak 2022). In this example embodiment, there was a main vessel, which was a cylinder that had an osmotic membrane fitted at the bottom and the top was open to ambient air (101). The osmotic membrane filtered seawater (102) and desalinated water collected at the bottom of the vessel (103). Anchors were used and could be flexible or rigid (104). A service shaft was dug on land near a steep sloped deep shore (105). An air pressure equalizer conduit (s) was used (106), and an underground reservoir was dug on land to collect fresh water (107). The critical depth (D) was below the sea surface, at which the pressure difference through the membrane was sufficient to start and sustain RO (abbreviated RO)

the desalination of drinking water, brackish water, or seawater. Its high water permeability and selectivity make it an effective tool for removing salts and impurities from water sources, thereby producing clean and safe drinking water. Despite the potential benefits, implementing these systems on a large scale is hindered by several challenges, including the expensive production of aquaporins, limited stability, manufacturing constraints, as well as operational limitations related to the membrane and desalination (Tang et al. 2013).

5 Nanotechnology Water Treatment Nanotechnology shows potential for improving membrane performance and efficiency due to the unique characteristics and shape of nanomaterials, but the immaturity of the technology raises questions about its practical application. Therefore, it is necessary to conduct quantitative analyses of important membrane parameters, such as fouling properties. Figure 4 presents the various types of nanotechnology used in desalination (Bhoj et al. 2021).

WO2013074669 A1 (2013), The current invention pertains to nanoparticles in general and, more specifically, but not exclusively, to films and filters including nanoparticles where the effective pore diameter between practically all nanoparticles is smaller than about 7 nm (Jaeger et al. 2013). In the US, 20,160,207,798 A1 Desalination was also accomplished using nanoporous graphene (Mahurin et al. 2019). They developed a method for passing saline water through a free-standing graphene sheet with pores as small as 1 nm and silicon-passivated pore edges. While in US20180207591A1, Nitrogen-doped graphene oxide quantum dots can be used in a TFC membrane. To improve the performance of the thin film composite membrane, graphene oxide quantum dots can be doped with nitrogen (Yu and Fathizadeh 2018). CN106215720B discloses a technique for manufacturing a UF membrane resistant to organic solvents, which incorporates graphene quantum dots as additives. The resulting UF membrane and its application are also described in the disclosure. As per the innovation, the process involves

Fig. 4  Nanomaterials types used in desalination technologies

Nanomaterials

Quantum Dots

Nanoparcles

Nanosheets

Nanotubes

Nanofibers

Others

Recent Patents and Modern Industrial Devices for Clean Water

introducing graphene quantum dot nanoparticles into the preparation of high molecular weight polyimide UF membranes. Subsequently, the graphene quantum dot-infused polyimide UF membrane undergoes modification through ethylenediamine crosslinking, leading to the synthesis of an organic solvent-resistant polyimide ultrafiltration membrane doped with graphene quantum dots (Baowei et al. 2016). The invention described in US20230032168A1 relates to sintered nanoparticle compounds with anti-pathogenic properties (Silveira 2023). The compounds are made of zeolite, silver nitrate (AgNO3), silver dioxide nanoparticles (Ag2O np), and graphene. Another aspect of the invention is enhanced granulated activated charcoal (EGAC) compounds, which are made of granulated activated charcoal, silver nitrate (AgNO3), silver dioxide nanoparticles (Ag2O np), and graphene. The compounds can be used in various applications, including enhanced filtration systems and pressurized wastewater filtration plants.

6 Solar Desalination Desalination and renewable energies, including wind energy, thermal and electrical solar energy, complement each other quite well. Desalination is frequently sought in areas with an abundance of solar energy. Such facilities are particularly ideal for decentralized operations in regions with poor infrastructure since places with established infrastructure often offer adequate conventional energy for desalination when the volume of water required per person is larger than 10 L per day (Do Thi et al. 2021; Ghazi et al. 2022). In contrast, in locations with inadequate infrastructure, electricity supply based on renewable energies is more dependable than power supply based on conventional energy sources, and people living in tiny villages in poor nations often require less than 10 L of domestic water per day (UNHR 2022). In WO2022158619 (2022), according to the previous art, the salt water desalination apparatus with a multi-stage construction comprises at least one evaporation plate in the device, and the evaporation plate is a plate with a wick formed on the back surface of the plate. As a result, the saltwater travels down toward the wick produced on the back side of the plate, where it evaporates from an energy source such as solar radiation and condenses into fresh water. An embodiment of the present invention’s brine desalination apparatus can lower manufacturing costs by decreasing parts and materials and simplifying the construction, as well as the forward evaporation unit that absorbs solar heat directly. It is possible to prevent deformation or damage to elements such as the spacer by giving the heat-insulating layer and the heat-conducting layer to the solar heat (Park 2022).

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Several Indian patents have addressed solar desalination (IN202241033629; 2022, IN202211033567; 2022 and IN202211033032; 2022) (Gangola et al. 2022; Kaviti et al. 2022; Sunori and Chaudhary 2022). IN202211033032 (2022), includes an evaporator is simply a piece of a water pool with a thickness greater than that of the desalinated water, and atomizers and branch lines of the fume and condensate release framework are positioned above the water pool. The outside layer of the evaporator’s water pool is coated with a film that has floating components molded as balls and may be used for water desalination in dry and waterless areas near oceans and seas. EP4015462 (2020), the current invention pertains to a solar-aided carbon membrane for a desalination system. The desalination device includes a carbon membrane body with a carbon surface and a structure of microchannels and/ or nanochannels, a liquid transportation structure of the carbon membrane body with a desalinated liquid, and a condenser placed above the carbon membrane body (Cruz et al. 2022). As per the disclosure’s illustrative embodiments, the desalination device is exemplified as a purification device. A schematic representation of this is provided in Fig. 5a. Additionally, Fig. 5b and c shows an enlarged sectional view of the carbon membrane body within the desalination device, which serves as an example of a purification device according to the disclosure’s illustrative embodiments. The US11505476B1 patent describes a sub-ambient solar desalination unit that comprises a solar pond alongside a pressure-reducing structure (Sherif et al. 2022). The solar pond is designed to receive saltwater and elevate its temperature through direct exposure to solar radiation while maintaining atmospheric pressure. The pressurereducing structure is connected to the solar pond to receive heated saltwater from it. The central segment of the pressure-reducing structure is configured to maintain a suitably decreased sub-ambient pressure, prompting a phase transition in the heated saltwater. This process leads to the generation of pure water vapor and a concentrated brine. A vapor outlet within the pressure-reducing structure is used to release the pure water vapor, which then enters a freshwater reservoir and undergoes condensation to transform it into pure liquid water. The concentrated brine solution is returned to the solar pond for recycling through an outlet section of the pressure-reducing structure. In CN107416931 (2017), the invention of a flexible self-adaptive focusing solar seawater desalination system is disclosed. This system comprises a seawater pump, a heat regenerator, a condenser, a flexible convex transparent water storage cavity, a heat collector, a flash evaporation tank, a water collection tank, a solar cell panel, a vacuuming system, and other components. The flexible self-adaptive focusing solar seawater desalination system is characterized by the formation of a convex lens after storing

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7 New Trends in Desalination and Water Treatment

Fig. 5  A schematic representation of a desalination apparatus, serving as an illustrative example of a purification device a alongside a desalination apparatus showcasing a purification device c including an enlarged cross-sectional view highlighting a carbon membrane body b all in accordance with descriptive embodiments of the present disclosure (Cruz et al. 2022)

saltwater in the flexible convex transparent water storage cavity. It is suitable for islands without power and underdeveloped regions (Handong et al. 2017). US20220410029A1 describes a system known as the direct-contact, spray-assisted evaporation and condensation (DCSEC) system, which is used for generating freshwater from seawater (Chen et al. 2022). The system consists of a heating block that heats the seawater, multiple evaporation and condensation stages that produce water vapors through flash evaporation, an evaporation-only stage that receives brine from the last stage of the plural evaporation and condensation stages, an input/output block that takes in the brine from the evaporation-only stage and discharges it outside the system, along with cooling water, and a pressure-swing regeneration block that collects the water vapors from the evaporation-only stage and generates a hot vapor that is then used to heat the seawater in the heating block.

The microbial fuel cell (MFC) has gained significant consideration from the research community in the last decade due to its potential for directly converting organic waste into energy via anodic microbial catalysis and microbial/ enzymatic/abiotic cathodic electrochemical processes. This track discusses various features of the technology, including its application and the consumption of energy production for practical needs (Santoro et al. 2017; Shanthi Sravan et al. 2021). US011298660B2 described a method for operating an electrochemical device that involves discharging concentrate reject periodically in a timed batch cycle and replacing it with feed water (Liang et al. 2022). A control module regulates a valve in the recycle line, which periodically opens to discharge concentrate reject in a batch cycle. Feed water is then introduced into the recycle line to replace the concentrate reject. The US20230063865A1 patent presents an electrochemical deionization system that can operate within a specific temperature range to prolong the system’s lifespan and improve its performance (Christensen et al. 2023). The system is designed to regulate the temperature of the solution stream (e.g., seawater or brackish water) flowing through the electrochemical deionization cells to maintain the desired operating temperature range. IN202211021312 (2022), disclosure is primarily concerned with microbial or bio-electrochemical processes. The invention is more precisely oriented to a microbial desalination cell, featuring a cathodic chamber containing a cathode impregnated with a perovskite oxide catalyst, an anodic chamber with an electrically connected anode to the cathode, and a desalination compartment. Furthermore, the current invention encompasses a separator cathode assembly for wastewater desalination, along with a corresponding technique for wastewater treatment. The cell described in this invention is cost-effective, produces a substantial power output, facilitates organic waste degradation, and enhances wastewater desalination efficiency (Tomar 2022). Capacitive desalination technology uses charged electrodes to adsorb ions in water, thereby achieving the goal of water purification. The ion concentration in the channel is significantly reduced as ions are gradually enriched in the electrodes on both sides. During electrode regeneration, the adsorbed ions are rapidly desorbed from the electrode surface and transported away by the water flow in the channel, resulting in the formation of concentrated water. Furthermore, residual chlorine and organic contaminants in water can also be absorbed by capacitive

Recent Patents and Modern Industrial Devices for Clean Water

desalination filters. However, previous art has been limited by the volume constraint of the capacitor desalination filter element, which limits the length of the flow channel. In CN110759438 (2020), a capacitive desalination filter element is disclosed, which includes a capacitive desalination unit with a raw water flow path positioned inside it (Xiaoping 2020). The Brayton cycle adsorption desalination system incorporates an adsorption desalination unit. This unit comprises an evaporator responsible for converting saline water into water vapor, an adsorbent bed that facilitates the adsorption and desorption of the water vapor, and a condenser tasked with transforming the water vapor back into distilled water. As per the US11311818 patent application filed in 2021, the Brayton cycle adsorption desalination system further includes a Brayton cycle unit. This unit encompasses a primary heat exchanger (PHE) and a cooler specially designed to lower the temperature of the output from the PHE (Fig. 6). The PHE establishes a connection between the adsorption desalination unit and the Brayton cycle unit. This arrangement enables the PHE to work as a source of heat for the adsorbent bed. The cooler serves as a link between the Brayton cycle unit and the adsorption desalination unit, facilitating the absorption of water by the evaporator (Almatrafi et al. 2022).

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Given the issues associated with water desalination and purification, innovative systems, techniques, and apparatus for water demineralization and purification with zero discharge are required to develop a sustainable and circular solution. A similar method would help improve water production in marine ecosystems and coastal habitats. US20220212955 (2021), in brief, the invention consists of demineralization systems and techniques of application (Shafie and Magnuson 2022). A heated gas source, such as flue gas, a gas cooling apparatus to cool the heated flue gas, a gas compressor to increase the pressure of the gas, a brine intake to import brine to the system, a heat exchanger to heat the brine, a spray nozzle or other drying system to disperse the heated brine and separate the water from the particulates, and a drying chamber to facilitate isolation of potable or distilled water from the brine and particulates When compared to currently existing demineralization systems, this method provides cost, waste reduction, and overall efficiency benefits. The US20230061678A1 patent application described a solvent extraction process that was developed for desalinating seawater (Chakrabarti 2023). This process utilized a specific type of polar organic solvents that exhibited a unique reverse solubility-temperature behavior, meaning that they had a high solubility for salt-free water at lower

Fig. 6  Brayton cycle adsorption desalination system (Almatrafi et al. 2022)

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temperatures but significantly lower solubility at higher temperatures. To desalinate the seawater, the solvents were added to the seawater or saline water at room temperature. The solvents dissolved the salt-free water, and the solvent–water phase was separated from the salt-rich aqueous phase. The solvent–water phase was then heated to a higher temperature to separate the relatively salt-free water. This desalination process was simple, fast, and energy-efficient. It also had several advantages over conventional methods, such as being ecologically safe. US20230017568A1 developed a method and system for treating desulfurization wastewater with zero discharge capabilities, suitable for various working conditions (Yu et al. 2023). The bottom outlet of a wastewater drying tower and the tail flue of a boiler were both connected to an inlet of a dust collector. The outlet of the dust collector was then linked to the flue gas inlets of a wastewater concentration tower and a desulfurization absorption tower. From there, the desulfurization absorption tower was connected to a chimney and a gypsum cyclone, while the wastewater concentration tower was linked to the former. The gypsum cyclone was connected to a filtrate water tank and a gypsum dewatering machine, which, in turn, was connected to a gas–liquid separating tank. Additionally, the flue gas port of the tail flue of the boiler was connected to the flue gas inlet of the wastewater drying tower. Figure 7 shows a schematic of the disclosure, a system for treating desulfurization wastewater with zero discharge capabilities, suitable for various working conditions. The adaptability of the US20230017568A1 disclosure to various flue gas components allows for the provision of distinct zero-discharge treatment methods for desulfurization wastewater, ensuring that the system operates with high reliability, energy efficiency, and economic viability under different working conditions. The method disclosed in WO2015174973A1 involves purifying processed water through a series of steps (Patel 2015). This includes providing processed water that contains a specific concentration of a dissolved gas and a dissolved ion, filtering the processed water to generate a filtered processed water with a lower concentration of the dissolved gas, and evaporating the filtered process water to generate a water vapor with a lower concentration of the dissolved ion compared to the initial concentration in the process water. The US20230059325A1 patent application described a hydroelectric power generation system that included one or more conduits extending from beneath the sea surface to a predetermined depth into the ground below the sea floor (Sadeh 2023a). Each conduit was connected to a turbine located at the underground distal end. The system also included an underground reservoir designed to collect seawater flowing through the conduit and the connected

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Fig. 7  A schematic of a system for treating desulfurization wastewater with zero discharge capabilities, suitable for various working conditions (Yu et al. 2023). The various components are labeled as follows: 1: Boiler; 2: Economizer; 3: Air preheater; 4: Dust collector; 5: Induced draft fan; 6: Desulfurization absorption tower; 7: Chimney; 8: Gypsum discharge pump; 9: Gypsum cyclone; 10: Gypsum dehydrator; 11: Gas–liquid separation tank; 12: Vacuum pump; 13: Filtrate water tank; 14: Filtrate water pump; 15: Wastewater collection tank; 16: Wastewater delivery pump; 17: Wastewater concentration booster fan; 18: Wastewater concentration tower; 19: Mist eliminator; 20: Spray layer; 21: Circulating pump; 22: Thick slurry tank; 23: Thick slurry pump; 24: Clarifier; 25: Spray water tank; 26: Spray water pump; and 27: Wastewater drying tower

turbine. This hydroelectric power generation system could be used as part of a distributed hydroelectric power generation system, which includes several hydroelectric power generation systems. In such a system, an underground reservoir was included to collect seawater flowing down through all of the conduits and connected turbines in the multiple hydroelectric power systems. Overall, this hydroelectric power generation system was designed to efficiently and

Recent Patents and Modern Industrial Devices for Clean Water

sustainably generate electricity using seawater as the energy source. The system was innovative and had several advantages over conventional power generation systems, such as being less dependent on fossil fuels and having a low environmental impact. Moreover, the US20230040672A1 patent application described a hydroelectric power generation system that included at least one penstock (Sadeh 2023b). The penstock extended through the sea floor to a predetermined depth into the ground below the sea floor. Each penstock was connected to a turbine located at the underground distal end. The system also included an underground reservoir designed to collect seawater flowing through the penstock and connected turbine. This hydroelectric power generation system could be used as part of a distributed hydroelectric power generation system, which includes several hydroelectric power generation systems. In such a system, an underground reservoir was included to collect seawater flowing down through all of the penstocks and connected turbines in the multiple hydroelectric power systems. Overall, this hydroelectric power generation system was designed to efficiently and sustainably generate electricity using seawater as the energy source. The system was innovative and had several advantages over conventional power generation systems, such as being less dependent on fossil fuels and having a low environmental impact. US20220168692 (2022) describes a method and system for cleaning semi-permeable membranes used in FO and RO processes. The invention involves implementing a pulsed-flow regime in the fluid stream, creating a higher shearing force for improved foulants evacuation. Additionally, a backward wash may be provided by injecting additional solution for a predetermined injection time in such a way that net driving pressure becomes RO opposite to normal PRO operation, resulting in a backward flow from the first side of the membrane to the second side of the membrane to lift and evacuate foulants (Liberman and Liberman 2022). The patent application US20220363570A1 (Chidambaran et al. 2022) describes procedures and assemblies for purifying or reducing the brine volume using an advanced vacuum distillation (AVMD) process. The AVMD process is designed to attain increased flux by directing vapors via an AVMD distillation unit. In one scenario, a tank circulates brine, housing one or more membrane pouches that are either immersed in the circulating brine or situated above the water level of the heated circulating brine. In different variations, the membrane pouches are positioned external to the tank holding the heated circulating brine while maintaining a connection with it. The circulating brine is heated to generate water vapor. Utilizing a vacuum, the water vapor is pulled through the membrane, allowing it to undergo condensation and subsequently

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be employed for additional advantageous purposes. This method is capable of concentrating brine to high levels, generating solids or crystals that can be separated and used. The advanced vacuum distillation process presented in this patent offers an innovative and efficient means of purifying or reducing the volume of brine. By circulating brine in a tank, heating it to create water vapor, and passing the vapor through a membrane using a vacuum, the process is able to achieve high levels of concentration and generate useful byproducts. This invention represents a significant advancement in the field of water treatment and provides a promising solution for managing brine waste. The US20230051291A1 patent application describes a system for carbon dioxide fixation consisting of an electrolytic cell and a settling tank (Sano et al. 2023). The electrolytic cell functions by electrolyzing seawater to generate sodium hydroxide. In the settling tank, the generated sodium hydroxide, concentrated seawater, and CO2 are mixed to form a reaction that results in the precipitation of magnesium carbonate. This process fixes the CO2 to magnesium present in the concentrated seawater. Overall, this system offers a simple and cost-effective approach to CO2 fixation using seawater as the primary source. The system could help mitigate CO2 emissions, a significant contributor to both global warming and climate change. Furthermore, the system’s reliance on seawater as a primary source makes it a readily available and renewable resource for this process, offering potential for widespread adoption. The invention described in US20230018348A1 pertains to a system for generating vapor that combines vapor–liquid ejector supercharging with flash vaporization technology (Yang et al. 2023). This system is used for waste heat utilization and steam generation. It consists of a vapor–liquid ejector, a flash vaporization tank, and an intermediate heat exchanger. The vapor–liquid ejector uses high-pressure steam to raise the temperature and pressure of low-pressure water that is absorbed from the flash vaporization tank. The pressure-increased water is then flashed into low-pressure saturated steam upon entering the flash vaporization tank. Any saturated water that is not flashed is collected at the bottom of the flash vaporization tank. By using a small portion of high-pressure steam, this system can generate multiple low-pressure flash vaporization saturated steam, which can be used for heavy oil thermal recovery, seawater desalination, or sewage treatment equipment. The system allows for the recovery and utilization of waste heat such as flue gas from a boiler, improving the economy of the thermal process. Additionally, the vapor source provided by this system is flexible and adjustable. The vapor source system described in this disclosure utilizes vapor–liquid ejector supercharging and flash vaporization technology to generate low-pressure flash vaporization saturated steam, while recovering and utilizing waste heat from sources such

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as flue gas of boilers. This system improves the economic efficiency of thermal processes and provides a flexible and adjustable vapor source for heavy oil thermal recovery, seawater desalination, and sewage treatment equipment.

8 Future Potentials and Challenges In 2021, according to the International Desalination Association (IDA), the worldwide operational volume for desalination reached 79.35 million cubic meters per day, and an additional 6.38 million cubic meters per day of new capacity were agreed upon within that same year (Belmehdi et al. 2023). Desalination is acknowledged as the water treatment method with the highest energy consumption, utilizing a total of 75.2 terawatt-hours of energy annually (Nassrullah et al. 2020). The energy necessary to generate 1 m3 of drinking water varies depending on the water source, ranging from 0.37 kWh/m3 for surface water to 8.5 kWh/m3 for seawater (Nassrullah et al. 2020). Despite the lower energy costs of treating groundwater and surface water, their supply is inadequate to meet the growing demand for freshwater, making seawater desalination the most viable solution for global water scarcity, despite its high energy costs. Renewable energy resources including wind, solar, and geothermal energy, have been researched and developed to desalinate seawater due to concerns over the high energy requirements and environmental impact of non-renewable energy sources (Shahid et al. 2023). While not all renewable energy sources are suitable for all desalination technologies and are subject to various factors, including accessibility, cost, infrastructure, and government regulations, they offer promising solutions for water security, energy sustainability, and environmental sustainability. Solar-powered desalination systems are being implemented in different regions globally. In a recent instance, an organization based in California employed solar desalination technology to clean 1.6 billion gallons of saline agricultural runoff in the drought-affected Central Valley, a region acclaimed for its productive soil (Wijewardane and Ghaffour 2023). At present, a substantial solar desalination project is undergoing the stages of design and construction within Saudi Arabia, featuring an overall capacity of 60,000 cubic meters per day. In addition, an innovative plug-andplay containerized solution has been commercialized, which operates off-grid utilizing solely solar energy to generate freshwater from seawater (Wijewardane and Ghaffour 2023). Nanotechnology has the potential to improve membrane performance and efficiency in desalination. Advanced functional materials exhibited promising efficiency in water and wastewater treatment (Shahid et al. 2019). Studies have suggested surface alteration and integration of nano-fillers

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to improve membrane performance and reduce fouling during water treatment. Surface modification techniques including physical adsorption, photo-initiated graft polymerization, atom transfer radical polymerization, and plasma graft polymerization, have been adopted and examined by researchers. However, integrating nanoparticles into the membranes is more favorable than surface modification. Nanoparticles enable enhanced manipulation of membrane structure and mechanisms related to fouling (Yasir et al. 2023). Most of the studies overlooked the potential issue of nanoparticle leaching from fabricated membranes. Further research on particle leaching is needed for the scale-up of these advancements. The major challenges in nanotechnology are the potential health and environmental risks associated with the production and use of nanomaterials and the need for standardized methods to assess the performance and safety of these materials. The small size and unique properties of nanoparticles make them more reactive and potentially hazardous than larger particles, raising concerns about their potential impact on the health of humans and the environment. The costs associated with desalination processes are affected by several factors, including maintenance, concentrate disposal, capital investment, energy, labor, and financing interest duties (Papapetrou et al. 2017). Among these, energy expenses generally constitute the most significant element of the overall cost of water production across all desalination methods. Thermal desalination methods like MSF, MED, and TVC use low-temperature heat for evaporation and electricity for pumping water, with energy costs accounting for almost 60% of entire production expenses in these processes (Alawad et al. 2023). In contrast, the energy expenditure associated with RO, the primary membranebased desalination technique, makes up roughly 44% of the complete water production expenses. The production costs of desalination systems powered by renewable energy vary based on the specific type of system. Within this group, the wave-powered RO unit exhibits the lowest average production cost at approximately 0.95 $/m3, followed by solar multi-effect distillation (MED), solar multi-stage flash (MSF), wind-powered RO, and wind-powered mechanical vapor compression (MVC) at 2.55, 3.00, 3.60, and 6.50 $/ m3, respectively (Alawad et al. 2023). Conversely, the photovoltaic (PV)–powered RO system holds the highest production cost within the realm of renewable-energy-powered desalination systems, averaging around 14 $/m3. Desalination processes play a significant role in meeting the growing demand for freshwater resources. However, the energy-intensive nature of these processes and factors such as energy costs, capital investment, maintenance, and financing interest rates can significantly impact production costs. Employing renewable energy sources to energize desalination systems can aid in mitigating the

Recent Patents and Modern Industrial Devices for Clean Water

environmental repercussions. Despite the higher production costs associated with renewable-energy-coupled desalination systems, their environmental benefits make them an attractive option, particularly in remote areas lacking access to electricity. Furthermore, technological advancements in desalination processes have the potential to reduce production costs and enhance their efficiency.

9 Conclusion The water-related technologies have made significant progress in the past two decades, with innovations in desalination processes, membrane technology, nanotechnology in water treatment, solar-power-driven desalination, etc. These advancements offered solutions to address the rising global demand for clean and safe water, which is a fundamental need for sustaining life and economic growth. However, despite these achievements, several issues and challenges exist, such as high costs, system efficiencies, and environmental concerns. Therefore, continuous research and development are required to overcome these challenges and ensure the accessibility of clean water. The development of sustainable and efficient water-related technologies will play a critical role in meeting this challenge and securing a better future. In conclusion, this chapter highlights the importance of staying informed with the latest advancements in water-related technologies to address the challenges of sustainable water management, ensuring access to clean and safe water.

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Index

A Activated carbon fiber, 122, 131 Activation, 245, 252, 255, 257–263 Active anode materials, 146 Active chlorine, 151, 152 Adsorption, 183–187, 195, 196, 227, 228, 232, 233, 235 Advanced oxidation, 117, 120, 137 Advanced Oxidation Process (AOP), 107, 114, 117–120, 137, 218, 219, 249, 258 Advanced Vacuum Distillation (AVMD), 277 Aerobic fluidized membrane bioreactor, 222 Air-lift multilevel circulation membrane bioreactor, 223 Alternative raw materials, 45 Anaerobic membrane bioreactor, 221, 224 Anodic Fenton, 117, 136, 137 Antibiotic, 96–103 Applicability, 150 Aquaculture, 95–97, 100–104 Asymmetric membrane, 44, 49 Atrazine, 120, 123 B Bimetallic catalyst, 162, 169, 172 Biochar, 159, 160, 165–167, 169–179 Biodegradation, 217, 218, 222–224 Bio-electrochemical reaction, 189 Biofilm, 221, 223 Biofouling, 218, 219, 221 Biomass treatment, 165 Biosourced material, 159 Boron-Doped Diamond (BDD), 120, 121, 123–137 C Capacitive deionization, 25–27, 32 Carbon electrode, 26, 31, 32, 34, 36 Carbon felt, 120, 123–135 Carbon materials, 29, 34–36 Cavitation, 110 Ceramic membrane, 41, 42, 44, 45, 48–52, 62 Charge efficiency, 29–32 Chemical Oxygen Demand (COD), 229–234 Chemical redox, 183, 184 Chromium, 183, 196 Clay, 41, 42, 44, 45, 52 Clean water production, 267, 269 Composite membrane, 59, 271, 272 Contaminant, 96, 97, 101, 103, 104 Conventional water treatment technology, 200, 201 Cr(III), 183–195 Cr(VI), 183–196

Current density, 228–231, 234 D Decentralization, 145, 146, 149–151, 154 Decontamination, 183, 184, 186, 187, 190, 194–196 Degradation, 107–111, 113–115 Dense Non-Aqueous Phase Liquid (DNAPL), 241–246, 248, 250, 252–257, 263 Desalination, 41, 42, 47, 51, 53, 57, 58, 62–64, 69, 70, 74–76, 80 Desalination performance, 26, 34, 35, 37 Design methodologies, 228, 230 Dew biological characteristics, 1 Dew chemical characteristics, 1, 22 Dew condensation, 3, 15, 17, 19, 21 Dew condenser shapes, 21 Dew physical characteristic, 1 Dew water, 1, 15, 21, 22 Domestic sewage, 217 Drinking water, 199, 200, 202, 211 Drinking water quality monitoring, 83–86, 90, 92 Droplet growth, 5 E Electrical conductivity, 234 Electrical double-layer, 25, 27 Electrochemical, 97, 101–104 Electrochemical anaerobic membrane bioreactor, 223 Electrochemical deionization, 274 Electrochemical desalination, 26 Electrochemical devices, 151 Electrochemical membrane bioreactor, 221, 223 Electrochemical oxidation, 145, 146, 152, 153 Electro-Fenton, 117–124, 128, 133–137 Electrolysis, 183, 187–190 Electrooxidation, 231 Electro-sorption, 26, 27, 35–37 Electrospun nanofiber, 75, 76, 78, 80 Electrostatic interaction, 63, 64 Empirical model, 229 Energy recovery, 268, 269 Environmentally friendly, 232 Environmentally technologies, 227 Etching, 74 F Fenton, 107, 108, 110–112, 115 Fenton-like reaction, 169, 177 Fenton process, 117–122, 134, 136, 137 Fenton reaction, 118, 119, 136, 137

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 K. Jlassi et al. (eds.), Clean Water: Next Generation Technologies, Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-031-48228-1

283

284 Fenton’s reagent, 117–120, 137 Fered Fenton, 117, 119, 136 Fish, 95–102, 104 Flocs pollutants, 229 Fluoroalkylsilane, 49 Forward osmosis membrane, 69–73, 75, 76, 78–80 Free radicals, 163, 173 G Groundwater, 239–245, 248–254, 256–258 H H2O2, 118–120, 136, 137 Heat exchanger, 270, 275, 277 Heavy ions monitoring, 88, 92 Heterogeneous catalysts, 160 Heterogeneous Fenton, 118 Heterogeneous •OH, 118–120, 122, 132–135 Hexachlorocyclohexane (HCH), 239, 240, 243, 250, 256 Hierarchical materials, 160 Hollow fiber, 46–49, 52 Hollow fibre membrane, 62 Homogeneous •OH, 118–120, 134–136 Hormone, 96–98, 101, 104 Hybrid processes, 115, 227 Hydrochar, 165 Hydrodynamic cavitation, 107, 110, 115 Hydrophobic membrane, 41, 42, 47, 52 Hydrothermal synthesis, 163, 165 Hydroxyl radical, 107, 110, 111, 117, 120, 121, 136 I Immobilization, 183, 184 Industrial wastewater, 200, 209, 217 Innovative technologies, 199, 200, 204, 211 Innovative water treatment technology, 199, 200 In Situ Chemical Oxidation (ISCO), 240, 252, 255, 257, 258 In situ Chemical Reduction (ISCR), 240, 248 Interfacial polymerization, 69, 72, 73 Ion-exchange membranes, 29, 32, 33 L Landfill leachate, 217, 223 Light rain biological characteristics, 2 Light rain chemical characteristics, 2, 22 Light rain collection, 2, 7 Light rain physical characteristics, 1, 2, 6 Lindane, 239–243, 245–249, 251, 253, 255, 262 Low-cost membrane, 45 M Membrane bioreactor, 217, 219, 223 Membrane cleaning, 219 Membrane distillation, 41, 42, 221, 224, 271 Membrane filtration, 268 Membrane fouling, 217, 220, 221 Membrane separation, 217, 218 Mesoporous silica, 159–161, 163–168, 173–176, 178, 179 Metal deposition, 162 Metal-organic frameworks, 57, 58 Microbial Fuel Cell (MFC), 218, 219, 223, 274

Index Microorganisms, 152 Microplastics, 199, 205 Micropollutant, 96–98 Mineralization, 107, 108, 110, 115, 117–134, 136, 137 Mixed-matrix membrane, 59–61 Molecularly Imprinted Polymers (MIPs), 102, 103 Monometallic catalyst, 172 Municipal wastewater, 217, 221 N Nanofiber-based membrane, 69, 75, 76, 79 Nanoplastics, 199, 207 Nanotechnology, 268, 272, 278, 279 Non-active anode materials, 146, 147, 154 Nucleation on liquids, 4, 5 Nucleation on solids, 4 O Organic pollutant mineralization, 162, 173 Organic pollutants, 117–123, 134, 136, 137 Osmotic membrane bioreactor, 221, 224 Ozonation, 109, 111–113, 116 Ozone, 107, 109–113, 115, 116 P Persulfate, 243, 248–251, 255, 257, 258, 262, 263 Pesticide, 95, 96, 100, 103 Pesticide monitoring, 86, 92 PH and temperature monitoring, 87, 92 Phase inversion, 44, 46–49, 52, 72, 73, 75, 79 Photocatalysis, 107, 108, 113–115, 191–196 Photocatalysts, 170, 176, 177 Photo-Fenton, 117–119 Picloram, 121 Plastic pollution, 199, 200, 209, 211 Porous carbon, 159 Portable sensors, 84, 85 Pressure-Retarded Osmosis (PRO), 269, 271, 277 R Reduction, 183–196 Remediation, 183, 186, 187, 239, 243, 245, 246, 249, 250, 252, 253, 255–263 Remote control, 90 Renewable energies, 146, 154, 273 S Sabiñánigo, 239, 241, 242 Sacrificial anode, 229 Salt rejection, 63–65 Secondary growth, 59–63, 65 Seeding treatment, 62 Sensor, 95–97, 101–104 Sewage wastewater, 217, 221, 223 Sintering, 41, 42, 45–48, 52 Smart sensors, 85, 87 Soil, 239–245, 249, 251–255, 257–263 Soil treatment, 145, 153 Soil washing, 145, 146, 153 Solar powered desalination, 278 Sonochemistry, 107, 115

Index Sulphate radical, 107, 114–116 Surface functionalization, 175 Surface modification, 42, 49, 52, 61, 62, 65 Surfactant, 243, 252–257, 261–263 Surfactant Enhanced Aquifer Remediation (SEAR), 252, 255 Sustainable, 268, 271, 275, 279 Sustainable development goals, 150 Synthesis designation, 59 T Thermal conversion, 159, 165, 178 Thin film composite membrane, 70, 72, 75 Toxicity, 122, 131, 132, 134, 136 Track-etching, 69, 72, 74 Treated water, 203

285 W Waste, 95–97, 100 Wastewater, 117–119, 121–123, 129, 131–134, 136, 137, 199–206, 209, 211 Wastewater treatment, 51 Water disinfection, 146, 154 Water flux, 58, 64, 65 Water pollutant monitoring, 84 Water-stable membrane, 58, 65 Water storage, 273, 274 Water treatment, 69, 74–76, 132 Wearable sensors, 84, 91, 92 Wet impregnation, 161, 166, 168, 172 Wireless sensor network, 83, 88, 92 Z Zero-Valent Iron (ZVI), 243, 245, 249

U Ultrafiltration, 273 Ultrasound, 107–111, 113, 115