Modeling technologies for desalination of brackish water — toward a sustainable water supply

Available online at www.sciencedirect.com

ScienceDirect Modeling technologies for desalination of brackish water — toward a sustainable water supply Soraya Honarparvar, Xin Zhang, Tianyu Chen, Chongzheng Na and Danny Reible Brackish groundwater is a largely untapped water resource that is available in much of the arid US. The low salinity of brackish water (1000–10 000 mg/L TDS) makes it a viable alternative water supply for municipal, industrial, and agricultural applications. Improvements in desalination technologies are required to fully utilize these waters. Electrodialysis (ED), capacitive deionization (CDI), and membrane capacitive deionization (MCDI) are tunable techniques with low energy requirements and operational costs and have advantages over conventional reverse osmosis (RO) in many applications. The aim of the current effort is identifying the conditions under which these technologies may be applicable and developing models of these processes for the purposes of optimization and design. A steady-state 2D ion transport model for ED and a 2D transient ion transport-adsorption model for (M)CDI are presented. The models are capable of successfully describing the concentrations and potential distributions in the processes during brackish water desalination. The models are used to describe the effects of thermodynamics, hydrodynamics, and operating conditions on ion transport in these systems. Address Texas Tech University, United States Corresponding author: Reible, Danny ([email protected])

Current Opinion in Chemical Engineering 2019, 26:104–111 This review comes from a themed issue on Energy, environment and sustainability: sustainability modeling Edited by Heriberto Cabezas

https://doi.org/10.1016/j.coche.2019.09.005 2211-3398/ã 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Introduction Fresh water resources are limited and account only for 3% of the water on the Earth, of which only one third is available as liquid water [1]. Climate change, population growth, intensive agricultural use, and industrial development put pressure on these limited freshwater resources and exacerbate water scarcity issues [2]. In the US, agricultural irrigation and thermoelectric power generation were the two main users of freshwater in 2015, although agricultural use is primarily consumptive and Current Opinion in Chemical Engineering 2019, 26:104–111

thermoelectric power generation is largely associated with temporary withdrawals [3]. The rapid growth of unconventional oil and gas production, attributed to the development of hydraulic fracturing and horizontal drilling techniques, has also increased the associated freshwater use in most of the shale basins in the US [4,5], many of which are largely dryland areas. Drylands that contain arid, semi-arid, and dry subhumid regions cover about 40% of the Earth’s land surface and more than 2 million km2 of the land area in the US [6]. The large quantities of freshwater use by agriculture, thermoelectric power, and oil and gas explorations in the arid and semi-arid areas of the western US can intensify local water shortages [4,7,8,9]. Often the quality of the water used in hydraulic fracturing and other non-potable uses is higher than what is needed [2]. Thus, exploring alternative water resources with lower quality to support a ‘fit-for-purpose’ water use model can help conserve freshwater. Enabling brackish water for irrigation, for example, could dramatically ease demands for high-quality freshwater and aid in the economic development of agricultural regions such as Southern High Plains of Texas [7]. In addition, poor-quality brackish waters could be upgraded for high quality potable water needs if treatment technologies are effective and efficient. Brackish water is a saline water with total dissolved solids (TDS) less than that of seawater. The US geological survey (USGS) has defined a TDS level between 1000–10 000 mg/L for brackish ground water in the US and categorized these waters according to their chemical compositions into four main groups. The first three groups include water types with sodium-bicarbonate, calcium-sulfate, and sodium-chloride as major components while the last group includes water containing a low concentration of a variety of cations and anions [10]. In some cases, brackish water can be used directly or after diluting with freshwater for hydraulic fracturing, power plants, and irrigation of high salt-tolerant crops [7,9,11]. However, the existence of minerals with concentrations above their solubilities increases salt precipitation and scaling issues. Thermodynamic analyses of phase equilibria in these saline waters help evaluate scaling, which can be used to assess potential uses or salinity management techniques [12,13,14]. Total or partial desalination of brackish water to remove scale-precipitating components or reduce TDS to manageable levels can make www.sciencedirect.com

Modeling technologies for desalination of brackish water — toward a sustainable water supply Honarparvar et al. 105

these alternative water resources suitable for industrial, agricultural, and municipal uses. The choice of desalination technique depends on many factors including the chemistry of feed water, final use of treated water, and energy consumption of the desalination process [15]. Desalination techniques can be categorized as thermal, chemical, membrane, electro-membrane, and electrochemical processes [16–18]. Widely used thermal desalinations technologies include multi-stage flash (MSF) and vapor compression (VC). The thermal processes are energy-intensive and are most suitable for areas with low energy costs such as the Middle East [19]. Ion exchange and solvent extraction are among the chemical desalination processes which can be used for removal of ions from saline waters but their efficiency is sufficiently high only at low ionic concentrations [20,21]. Membrane techniques include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). These are pressure driven processes to remove particles, bacteria, and salts from water via size exclusion through membranes with different pore sizes [16]. RO is a widely used technique due to its relatively low energy consumption compared to thermal processes. The technology is mature and accounts for 65% of the installed desalination capacity in the world [22]. However, high-pressure operations and the sensitivity of membranes to the quality of feed water increase both capital and operational costs. These challenges encourage the exploration of electro-membrane and electrochemical desalination techniques for brackish water [18]. In electro-membrane technologies such as electrodialysis (ED) and electrodialysis reversal (EDR), ion exchange membranes (IEMs) are used. IEMs pass counterions (ions with opposite charge to that of the fixed charge groups of the membranes) but block co-ions (ions with the same charge to that of fixed charge groups of the membranes). In ED (R), an electric field provides the driving force for selective transport of ions through IEMs and desalinating water [16]. Capacitive deionization (CDI) is an emerging electrochemical process which involves the adsorption of ions into porous electrodes under an electrostatic field and has the potential advantage of eliminating the need for membranes and the associated pretreatment steps [23,24]. CDI can also be used with IEMs to improve adsorption capacity although with the disadvantage of potential increasing pretreatment requirements. This review focuses on ED, CDI, and membrane CDI (MCDI) processes and modeling approaches for their optimization and design. The review discusses the unique attributes of these techniques that may make them reliable options for brackish water desalination.

ED process ED is a low-pressure electro-membrane technique and relative to RO, requires small energy input for www.sciencedirect.com

desalination of low salinity brackish water [19,25]. Optimizing the operating conditions of ED can significantly improve the energy consumption of the system, especially for desalination of feed water with higher salinity [26]. Compared to RO, membranes used in ED have higher chemical and mechanical stability and can sustain higher temperatures [27,28]. Hence, less pretreatment and additive chemicals are required for ED. The plate and frame configuration of ED means the membrane treatments can be implemented relatively simply compared to the spiral wound configuration of RO. In general, less biofouling and mineral scaling occur on membranes and they can further be controlled by switching to reverse mode. The quality of the desalinated water can be adjusted by changing imposed electrical potential, enabling ED for partial desalination of saline water. Because of the electrical nature of the process, ED is also capable of selective removal of ions, for example, divalent ions which are often the source of precipitation and scale. The separation efficiency in ED relies on cell design, system hydrodynamics, membrane properties, and operating conditions. We develop a 2D ion transport model for ED with the aim of identifying and optimizing the effective parameters for ion removal. The ionic fluxes are described using the Nernst-Planck (NP) equation with Teorell’s diffusion for high concentration and with Fick’s diffusion for dilute solutions [29–31]. To investigate the hydrodynamic effects, both spacer-free and spacer-filled cells are modeled and the laminar flow Navier-Stokes (NS) equations are solved to identify the velocity profiles. No-slip boundary conditions are assumed on surfaces of IEMs and spacer filaments [32]. Figure 1a represents a schematic of the spacer-free cell. The non-ideal solution effects caused by higher ionic concentrations are modeled using the polyelectrolyte nonrandom two-liquid (polyelectrolyte NRTL) activity coefficient model [33]. Substituting the NP equation in molar balance equation at the steady-state (st-st) condition results in a set of N equations and N + 1 unknowns including the concentration of N species and potential distribution in the cell. The equations can be solved with the additional constraint of electroneutrality. Local electrochemical equilibrium known as Donnan equilibrium is applied at IEMs-solution interfaces causing step changes in concentrations and potential in these regions [34]. The developed model accounts for co-ion transport through membranes and relaxes the ideal membrane assumptions applied in prior modeling efforts [35,36]. The experimentally measured current density versus electrical potential curves in ED show a low voltage region with a linear increase in current with potential (known as ohmic regime) followed by a plateau (known as limiting current density), and end with a linear increase at high potential (known as overlimiting current density). Our model is applicable to ED operated in the ohmic regime. Current Opinion in Chemical Engineering 2019, 26:104–111

106 Energy, environment and sustainability: sustainability modeling

Figure 1

(a)

(b) Concentrate outflow

Diluate Concentrate outflow outflow CMg2+,inlet/CNa+, inlet

= 0.25

to Na percentage removal ratio

2.1

2

1.9

1.8

Mg

2+

+

Anode

Anion exchange membrane

Cation exchange membrane

Cathode

2.2

1.7

Inlet Feed

1.6 2

4

6

8

10

Cell length, cm

(c) 3 CMg2+,inlet/CNa+, inlet

= 0.25

2.5

2.25

+

to Na percentage removal ratio

2.75

Mg

2+

2

1.75

1.5 0.4

0.6

0.8

1

1.2

Cell potential, V Current Opinion in Chemical Engineering

(a) A schematic of the spacer-free ED cell, (b) The Mg2+ to Na+ selective percentage removal ratio versus cell length in the diluate channel of the spacer-free cell at V = 0.3 V and feed solution with ionic strength of 1779 mol/m3, (c) The Mg2+ to Na+ selective percentage removal ratio versus cell potential in the diluate channel of the spacer-free cell at L = 2 cm and feed solution with ionic strength of 1779 mol/m3.

The 2D ion transport model is capable of qualitatively describing the concentration and potential distributions in both spacer-free and spacer-filled cells. The modeling results for an aqueous NaCl solution showed that the impacts of the solution non-ideality are minor for the Current Opinion in Chemical Engineering 2019, 26:104–111

salinity range of brackish water. Using spacers in channels results in higher limiting current densities than the current obtained in the spacer-free cell. This increase in current density is attributed to the enhanced cross-channel mixing in the spacer-filled cell. The model has been employed for www.sciencedirect.com

Modeling technologies for desalination of brackish water — toward a sustainable water supply Honarparvar et al. 107

an aqueous Na+-Mg2+-Ba2+-SO42 -Cl quinary solution to evaluate the ability to selectively remove scale precipitating ions. The results indicate that cell length, imposed electrical potential, the use of spacers, the ion concentrations and total ionic strength in the feed solution, and membrane properties affect the selective removal of ions in the cell. Increases in divalent ion concentrations and Donnan potential drops at the IEMs-solution interfaces benefit selective removal of divalent to monovalent ions in the cell. Increases in the cell length and imposed electrical potential decrease the selective Mg2+ to Na+ removal in the diluate channel of the spacer-free cell as demonstrated in Figure 1b and c, respectively. To minimize the required membrane surface, ED units are preferred to be operated at high electrical potential, increasing the possibility of reaching limiting and overlimiting current regimes. Thus, the model needs to be extended to account for the phenomena taking place in these high current regimes including water splitting, gravitational convection, and electro-convection [37,38]. Such effort involves replacing electroneutrality by Poisson equation due to increases in thicknesses of space charge regions, correcting the NS equations to account for electrostatic body forces, accounting for water dissociation reactions, and considering solution density changes. The developed model can be employed to characterize performance of an ED cell operated in the ohmic regime and for designing experiments to optimize the cell performance. However, for meaningful comparison of the modeling results with experimental data, the model framework should be improved to describe the flow behavior in 3D, take into account the effects of spacer geometry, consider biofouling and mineral fouling on the membranes and spacers, account for water transport through the membranes, and be expanded to more and different membrane types.

(M)CDI process CDI is a competitive technology for desalination of low salinity brackish water due to the low input potential and low-pressure operating conditions required [39,40]. CDI is a membrane-less technique and thus does not require pre-treatment to prevent membrane fouling. The salinity of CDI effluent can be tuned by changing operation conditions, allowing fit-for-purpose desalination [41]. Similar to ED, the inorganic and organic fouling can be controlled by switching the polarity of the electrodes and using pulsed field in CDI. In general, less fouling and scaling issues are observed for CDI compared to membrane techniques such as RO [42,43]. CDI can also provide selective removal of ions based on the ionic charge and hydrated radius [44,45]. MCDI contains IEMs between spacers and electrodes to allow easy access of counterions and prevent the www.sciencedirect.com

penetration of the co-ions, improving the salt removal ratio of the cell. In MCDI, selective ion removal can be achieved by tailoring the membrane properties [46,47]. The use of IEMs in MCDI cell decreases the extent of Faradaic reactions occurring in the cell and improves the charge efficiency of the process [48–50]. However, the high cost of ion exchange membranes [51] increases the capital and maintenance costs of MCDI compared to CDI. CDI and MCDI are emerging technologies and there are limitations on successful coupling of the electrode pairs into stacks, and stacks into modules, to scale up the process. Enhancing the long-term stability of the electrodes without increasing the total cost is another challenge for both techniques [52]. The energy demand of the (M) CDI processes have been compared with RO and several studies have demonstrated lower energy consumption for desalination of low salinity brackish water with (M)CDI [53,54,55]. However, comparing the energy consumption of a lab-scale (M)CDI and a large-scale RO may not provide a valid conclusion due to the more comprehensive energy needs in a full-scale system [56]. Here we use a model to compare CDI and MCDI performance. (M)CDI is described with a fully coupled 2D model for ion transport and adsorption behavior in the cell during charging. For both CDI and MCDI cells, the electrodes are modeled as a series of macropores through which ions are transported to the collection surface present in micropores. Chemically modified electrodes have been investigated in the literature and are shown to improve the ion removal in (M)CDI cells [57,58]. However, the focus of the current effort is modeling commercially available carbon cloth electrodes. The ionic fluxes in channel and in electrode macropores are described using the NP equation. The ion adsorption in electrode micropores is described using the Nernst equation. The Darcy’s law is employed to calculate the flow velocity in the spacer-filled channel treated as a saturated porous media [32]. In MCDI, the NP equation is used to calculate the ionic fluxes in non-ideal IEMs accounting for co-ion transport through membranes as well. Donnan equilibrium is applied at the IEMs-solution interfaces. Figure 2a illustrates a half CDI cell containing a half of spacer-filled channel and an electrode. Because of electroneutrality, the concentration distribution in both halfcells of a CDI cell are identical. Figure 2b shows the change of ion concentration in the effluent of the half-cell from 50 to 3000 s with an influent concentration of 20 mol/m3. Initially, the electrode experiences a high adsorption rate in the micropores of electrodes, resulting in a rapid decrease in ion concentration. As micropores become increasingly saturated, the effluent concentration asymptotically increases back to the influent concentration of 20 mol/m3. As shown in Figure 2c, increases in the imposed potential slows the rate of system equilibration. Current Opinion in Chemical Engineering 2019, 26:104–111

108 Energy, environment and sustainability: sustainability modeling

Figure 2

(b)

(a)

0.8

y = 0.8 mm

Vertical line at the exit 0.7

Porous electrode

0.6

Inflow

y-Direction, mm

y = 0.4 mm

Outflow

Spacer-filled channel y x

0.5

0.4

0.3

Symmetric line 0.2

0.1

(c)

0 0

20

5

10 15 Concentration, mol/m3

20

18

Effluent concentration, mol/m3

16 14 12 10 8 6 4 2 0 0

500

1000

1500

2000

2500

3000

Time, s Current Opinion in Chemical Engineering

(a) The schematic of the half-CDI cell, (b) Concentration distribution in the vertical line at the exit of the half CDI cell at V = 1 V, Q = 83.33 mm3/s, and c0 = 20 mol/m3, ( ) at t = 50 s, ( ) at t = 500 s, ( ) at t = 800 s, ( ) at t = 1000s, ( ) at t = 1500s, and ( ) at t = 3000 s, (c) Transient concentration distribution of outflow for initial concentration of c0 = 20 mol/m3 and inflow flow rate of Q = 83.33 mm3/s, ( ) at V = 0.6 V, ( ) at V = 0.8 V, and ( ) at V = 1.0 V.

The use of MCDI increases the rate of desalination and increases salt removal efficiency relative to CDI. The model describes 2D concentration and potential distributions inside the cell, which can neither be measured in the lab, nor have they been simulated well by prior models [59,60,61]. The overall energy efficiency of the system is a strong function of the quality of the effluent water and the degree of saturation achieved in the electrodes. The model can be used to optimize the energy efficiency, which is often achieved by cycling the system more rapidly rather than allowing the electrodes achieve near saturation. Current Opinion in Chemical Engineering 2019, 26:104–111

The modeling framework needs to be extended to multicomponent solutions to analyze selective ion removal. Adjustments are also necessary to expand the modeling framework to account for Faradaic reactions and effects of pore size distribution in the electrodes. The developed model can qualitatively represent the experimental data measured for (M)CDI cells and can be used to identify the critical parameters affecting the performance of the cells. However, the simplifying assumptions used in the modeling framework and the lack of key characteristics associated with the membranes www.sciencedirect.com

Modeling technologies for desalination of brackish water — toward a sustainable water supply Honarparvar et al. 109

and electrodes make the exact prediction of experimental data challenging.

Conclusion Meeting future demands for water requires the exploitation of non-traditional sources of water. The relatively low salinity of brackish groundwater makes desalination feasible but better process design and optimization is required to fully utilize available technologies. ED and (M)CDI have the potential to reduce the cost of desalination by simplifying pretreatment and promoting selective ion removal. A 2D ion transport model suggest that the non-ideal solution impacts on ion transport in ED are minor. However, hydrodynamics plays a significant role and using spacers in the channel increases the limiting current density values in the cell. The model is used to investigate the effective parameters for selective divalent ion removal. The results indicate that decreasing the cell length and cell potential enhances the selectivity toward divalent ions. The developed modeling framework is limited to an ED cell operated in the ohmic regime and further improvements are required to expand the model for limiting and overlimiting current transfer. A 2D transient model with coupled transport and adsorption is developed for a spacer-filled (M)CDI cell and used to estimate concentration and potential distributions in the cell. The model can be used to investigate the adsorption and transport phenomena in the cell and adjust the operating conditions to achieve optimal desalination performance. Comparing MCDI and CDI indicates that using IEMs in the MCDI improves the ion removal ratio compared to the membrane-less CDI cell at the cost of potential requiring greater water pretreatment. The current model does not account for Faradaic reactions and pore size distribution effects in electrodes. The model does not currently simulate multicomponent solutions and ion selectivity.

Conflict of interest statement Nothing declared.

Acknowledgements The authors gratefully acknowledge the financial support of the Maddox Foundation and the Donovan Maddox Distinguished Engineering Chair Endowment.

References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as:  of special interest  of outstanding interest 1.

Fennell A: Freshwater: supply concerns continue, and uncertainties complicate planning. Government Accountability Office, Tech. Rep. GAO-14-430. 2014 . Available: https://www. gao.gov/assets/670/663343.pdf.

www.sciencedirect.com

2.

Connor R: “Managing Water Under Uncertainty and Risk: The United Nations World Water Development Report 4,” UNESCO Reports. . Available: 2012 http://www.unesco.org/new/fileadmin/ MULTIMEDIA/HQ/SC/pdf/WWDR4%20Volume%201-Managing %20Water%20under%20Uncertainty%20and%20Risk.pdf.

3.

Dieter MAMC, Caldwell RR, Harris MA, Ivahnenko TI, Lovelace JK, Barber NL, Linsey KS: Estimated use of water in the United States in 2015. US Geol Surv Circ 2018, 1441 Available: https:// pubs.usgs.gov/circ/1441/circ1441.pdf.

4.

Kondash AJ, Lauer NE, Vengosh A: The intensification of the water footprint of hydraulic fracturing. Sci Adv 2018, 4 eaar5982.

5.

Reible DD, Honarparvar S, Chen C-C, Illangasekare TH, MacDonell M: Environmental impacts of hydraulic fracturing. Environmental Technology in the Oil Industry. Springer; 2016:199-219.

6.

White RP, Nackoney J: Drylands, People, and Ecosystem Goods and Services: a Web-based Geospatial Analysis. . Available: World Resources Institute; 2003 http://pdf.wri.org/drylands.pdf.

7. 

Uddameri V, Reible D: Food-energy-water nexus to mitigate sustainability challenges in a groundwater reliant agriculturally dominant environment (GRADE). Environ Prog Sustain Energy 2018, 37:21-36 The study focuses on the southern high plains of Texas (SHP) and evaluates the potential use of the brackish groundwater (BGW) in this agricultural area. Depending on the chemistry of the BGW, the study proposes direct use, dilution with fresh water, and desalination of the BGW prior to industrial and agricultural uses. The significance of the study is the evaluation of BGW as an alternative water supply to enhance the lifetime of fresh water resources. 8.

Averyt JFK, Huber-Lee A, Lewis A, Macknick J, Madden N, Rogers J, Tellinghuisen S: Freshwater Use by US Power Plants: Electricity’s Thirst for a Precious Resource. . Available: 2011 https://www.ucsusa.org/sites/default/files/legacy/assets/ documents/clean_energy/ew3/ ew3-freshwater-use-by-us-power-plants.pdf.

9.

Mauter PJJAM, Burton A, Cafaro DC, Chen W, Gregory KB, Jiang G, Li Q, Pittock J, Reible D, Schnoor J: Regional variation in water-related impacts of shale gas development and implications for emerging international plays. Environ Sci Technol 2014, 48:8298-8306.

10. Stanton DWAJS, Brown CJ, Moore RB, McGuire VL, Qi SL,  Harris AC, Dennehy KF, McMahon PB, Degnan JR: Brackish Groundwater in the United States. US Geological Survey; 2017:2330-7102 In this report prepared by the US Geological Survey, a comprehensive assessment of the distribution, chemistry, and physical properties of the brackish ground water (BGW) in the US is provided. The significance of this report is the establishment of a comprehensive database for BGW characteristics in the US. 11. Harto C, Finster M, Schroeder J, Clark C: Saline Water for Power Plant Cooling: Challenges and Opportunities. Argonne, IL (United States): Argonne National Lab; 2014. 12. Saravi SH, Honarparvar S, Chen C-C: Modeling aqueous electrolyte systems. Chem Eng Prog 2015, 111:65-75. 13. Honarparvar S, Saravi SH, Reible D, Chen CC: “Comprehensive thermodynamic modeling of saline water with electrolyte  NRTL model: a study on aqueous Ba2+-Na+-Cl -SO42quaternary system," (in Multi-Language). Fluid Phase Equilib 2017, 447:29-38 The study uses the eNRTL activity coefficient model and develops a comprehensive thermodynamic framework for the aqueous Ba2+-Na+Cl -SO42 quaternary system to calculate phase equilibria properties. The system under study is mainly associated with sulfate scaling and the developed framework is essential in the calculation of scale precipitations. 14. Honarparvar S, Saravi SH, Reible D, Chen C-C: Comprehensive thermodynamic modeling of saline water with electrolyte  NRTL model: a study of aqueous Sr2+-Na+-Cl -SO42 quaternary system. Fluid Phase Equilib 2018, 470:221-231 A comprehensive thermodynamic model is developed for the aqueous Sr2+-Na+-Cl -SO42 quaternary system based on the eNRTL model to enable the scale precipitation predictions. The investigated system is one of the main subsystem associated with sulfate scaling and the accurate calculations of phase equilibria provided by this study is the key to prevent fouling and costly remedial processes. Current Opinion in Chemical Engineering 2019, 26:104–111

110 Energy, environment and sustainability: sustainability modeling

15. Fritzmann C, Lo¨wenberg J, Wintgens T, Melin T: State-of-the-art of reverse osmosis desalination. Desalination 2007, 216:1-76. 16. Younos T, Tulou KE: Overview of desalination techniques. J Contemp Water Res Educ 2005, 132:3-10. 17. Bajpayee A, Luo T, Muto A, Chen G: Very low temperature membrane-free desalination by directional solvent extraction. Energy Environ Sci 2011, 4:1672-1675. 18. Mohsen MS, Al-Jayyousi OR: Brackish water desalination: an alternative for water supply enhancement in Jordan. Desalination 1999, 124:163-174. 19. Schenkeveld MM, Morris R, Budding B, Helmer J, Innanen S: Seawater and Brackish Water Desalination in the Middle East, North Africa and Central Asia: A Review of Key Issues and Experiences in Six Countries. Nimes, Franc¸a: Relato´rio te´cnico, Banco Mundial; 2004. 20. Nishihama S, Onishi K, Yoshizuka K: Selective recovery process of lithium from seawater using integrated ion exchange methods. Solvent Extr Ion Exchange 2011, 29:421-431.

theoretical framework to model overlimiting ion transport in the ED cell is described. This study offers a better understanding of the overlimiting ion transport and addresses the key effects that should be studied further. 38. Urtenov MA-K, Kirillova EV, Seidova NM, Nikonenko VV: Decoupling of the nernst planck and poisson equations. Application to a membrane system at overlimiting currents. J. Phys. Chem. B 2007, 111:14208-14222. 39. Li H, Gao Y, Pan L, Zhang Y, Chen Y, Sun Z: Electrosorptive desalination by carbon nanotubes and nanofibres electrodes and ion-exchange membranes. Water Res 2008, 42:4923-4928. 40. Kim Y-J, Hur J, Bae W, Choi J-H: Desalination of brackish water containing oil compound by capacitive deionization process. Desalination 2010, 253:119-123. 41. Zhao R, Biesheuvel P, Miedema H, Bruning H, Van der Wal A: Charge efficiency: a functional tool to probe the double-layer structure inside of porous electrodes and application in the modeling of capacitive deionization. J Phys Chem Lett 2009, 1:205-210.

21. de los Rı´os AP, Hernandez-Fernandez F, Lozano L, Sanchez S, Moreno J, Godinez C: Removal of metal ions from aqueous solutions by extraction with ionic liquids. J Chem Eng Data 2009, 55:605-608.

42. Kerwick M, Reddy S, Chamberlain A, Holt D: Electrochemical disinfection, an environmentally acceptable method of drinking water disinfection? Electrochim Acta 2005, 50:52705277.

22. Burn MHS, Zarzo D, Olewniak F, Campos E, Bolto B, Barron O: Desalination techniques—a review of the opportunities for desalination in agriculture. Desalination 2015, 364:2-16.

43. Perez-Roa RE, Tompkins DT, Paulose M, Grimes CA, Anderson MA, Noguera DR: Effects of localised, low-voltage pulsed electric fields on the development and inhibition of Pseudomonas aeruginosa biofilms. Biofouling 2006, 22:383390.

23. Hemmatifar A, Stadermann M, Santiago JG: Two-dimensional porous electrode model for capacitive deionization. J Phys Chem C 2015, 119:24681-24694. 24. Knust KN, Hlushkou D, Tallarek U, Crooks RM: Electrochemical desalination for a sustainable water future. ChemElectroChem 2014, 1:850-857. 25. Strathmann H: Assessment of electrodialysis water desalination process costs. In Proceedings of the International Conference on Desalination Costing; Limassol, Cyprus: 2004:3254. 26. Chehayeb KM, Lienhard JH: On the electrical operation of batch electrodialysis for reduced energy consumption. Environ Sci Water Res Technol 2019, 5:1172-1182.

44. Zhao R, Van Soestbergen M, Rijnaarts H, Van der Wal A, Bazant M, Biesheuvel P: Time-dependent ion selectivity in capacitive charging of porous electrodes. J Colloid Interface Sci 2012, 384:38-44. 45. Hou C-H, Huang C-Y: A comparative study of electrosorption selectivity of ions by activated carbon electrodes in capacitive deionization. Desalination 2013, 314:124-129. 46. Kim Y-J, Choi J-H: Selective removal of nitrate ion using a novel composite carbon electrode in capacitive deionization. Water Res 2012, 46:6033-6039.

27. Pilat B: Practice of water desalination by electrodialysis. Desalination 2001, 139:385-392.

47. Yeo J-H, Choi J-H: Enhancement of nitrate removal from a solution of mixed nitrate, chloride and sulfate ions using a nitrate-selective carbon electrode. Desalination 2013, 320:1016.

28. Lee H-J, Park J-S, Moon S-H: A study on fouling mitigation using pulsing electric fields in electrodialysis of lactate containing BSA. Korean J Chem Eng 2002, 19:880-887.

48. Landon J, Gao X, Omosebi A, Liu K: Impact of improvements in energy efficiency in capacitive deionization systems. Meeting Abstracts 2015, 16 1214-1214: The Electrochemical Society.

29. Koryta J, Dvora´k J, Kavan L: Principles of Electrochemistry. John Wiley & Sons Inc; 1993. 30. Newman J, Thomas-Alyea KE: Electrochemical Systems. John Wiley & Sons; 2012. 31. Teorell T: Transport processes and electrical phenomena in ionic membranes. Prog Biophys Biophys Chem 1953, 3:305-369. 32. Bird RB, Stewart WE, Lightfoot EN: Transport Phenomena. John Wiley & Sons; 2007. 33. Yu NHY, Chen C-C: Nonrandom two-liquid activity coefficient model for aqueous polyelectrolyte solutions. J Fluid Phase Equilib 2019, 497:1-9. 34. Donnan FG: The theory of membrane equilibria. Chem Rev 1924, 1:73-90. 35. Probstein RF: Physicochemical Hydrodynamics: An Introduction. Butterworth-Heinemann; 2013. 36. Benjamin MM, Lawler DF: Water Quality Engineering: physical/ chemical Treatment Processes. John Wiley & Sons; 2013. 37. Nikonenko NDPV, Belova EI, Sistat P, Huguet P, Pourcelly G,  Larchet C: Intensive current transfer in membrane systems: modelling, mechanisms and application in electrodialysis. Adv Colloid Interface Sci 2010, 160:101-123 The study provides a review of the four main mechanisms causing overlimiting current densities in an electrodialysis (ED) cell. The Current Opinion in Chemical Engineering 2019, 26:104–111

49. Tang W, He D, Zhang C, Kovalsky P, Waite TD: Comparison of Faradaic reactions in capacitive deionization (CDI) and membrane capacitive deionization (MCDI) water treatment processes. Water Res 2017, 120:229-237. 50. Kim KTY-H, Chang J, Sharma K, Yiacoumi S, Mayes RT, Bilheux HZ, Santodonato LJ, Tsouris C: Potential limits of capacitive deionization and membrane capacitive deionization for water electrolysis. Sep Sci Technol 2019:1-14. 51. Yee RS-L, Rozendal RA, Zhang K, Ladewig BP: Cost effective cation exchange membranes: a review. Chem Eng Res Des 2012, 90:950-959. 52. Welgemoed T, Schutte C: Capacitive deionization technologyTM: an alternative desalination solution. Desalination 2005, 183:327-340. 53. Suss M, Porada S, Sun X, Biesheuvel P, Yoon J, Presser V: Water desalination via capacitive deionization: what is it and what can we expect from it? Energy Environ Sci 2015, 8:2296-2319. 54. Zhao R, Porada S, Biesheuvel P, Van der Wal A: Energy consumption in membrane capacitive deionization for different water recoveries and flow rates, and comparison with reverse osmosis. Desalination 2013, 330:35-41. 55. Długołę cki P, van der Wal A: Energy recovery in membrane capacitive deionization. Environ Sci Technol 2013, 47:49044910. www.sciencedirect.com

Modeling technologies for desalination of brackish water — toward a sustainable water supply Honarparvar et al. 111

56. Qin ADM, Epsztein R, Patel SK, Owoseni O, Walker SW,  Elimelech M: Comparison of energy consumption in desalination by capacitive deionization and reverse osmosis. Desalination 2019, 455:100-114 The study compares the energy consumptions for desalination of low salinity brackish water with capacitive deionization (CDI) and reverse osmosis (RO) processes. Equal plant size and capacity and similar desalination performance are considered for both systems. 57. Biesheuvel P, Hamelers H, Suss M: Theory of water desalination by porous electrodes with immobile chemical charge. Colloids Interface Sci Commun 2015, 9:1-5. 58. Gao X, Porada S, Omosebi A, Liu K-L, Biesheuvel P, Landon J: Complementary surface charge for enhanced capacitive deionization. Water Res 2016, 92:275-282.

www.sciencedirect.com

59. Guyes EN, Shocron AN, Simanovski A, Biesheuvel P, Suss ME: A one-dimensional model for water desalination by flow-through electrode capacitive deionization. Desalination 2017, 415:8-13. 60. Biesheuvel P, Zhao R, Porada S, Van der Wal A: Theory of membrane capacitive deionization including the effect of the electrode pore space. J Colloid Interface Sci 2011, 360:239-248. 61. He F, Biesheuvel P, Bazant MZ, Hatton TA: Theory of water  treatment by capacitive deionization with redox active porous electrodes. Water Res 2018, 132:282-291 A model is proposed for ion concentration distribution in the electrodes of the Faradaic capacitive deionization (FaCDI) cell, in which the electrode surfaces are functionalized with redox polymers. The modeling results indicate that the FaCDI provides higher salt adsorption capacity compared to CDI.

Current Opinion in Chemical Engineering 2019, 26:104–111