Energy Consumption of Brackish Water Desalination: Identifying the Sweet Spots for Electrodialysis and Reverse Osmosis

Electro-driven technologies are viewed as a potential alternative to the current state-of-the-art technology, reverse osmosis, for the desalination of brackish waters. Capacitive deionization (CDI), based on the principle of electrosorption, has been intensively researched under the premise of being energy efficient. However, electrodialysis (ED), despite being a more mature electro-driven technology, has yet to be extensively compared to CDI in terms of energetic performance. In this study, we utilize Nernst-Planck based models for continuous flow ED and constant-current membrane capacitive deionization (MCDI) to systematically evaluate the energy consumption of the two processes. By ensuring equivalently sized ED and MCDI systems-in addition to using the same feed salinity, salt removal, water recovery, and productivity across the two technologies-energy consumption is appropriately compared. We find that ED consumes less energy (has higher energy efficiency) than MCDI for all investigated conditions. Notably, our results indicate that the performance gap between ED and MCDI is substantial for typical brackish water desalination conditions (e.g., 3 g L-1 feed salinity, 0.5 g L-1 product water, 80% water recovery, and 15 L m-2 h-1 productivity), with the energy efficiency of ED often exceeding 30% and being nearly an order of magnitude greater than MCDI. We provide further insights into the inherent limitations of each technology by comparing their respective components of energy consumption, and explain why MCDI is unable to attain the performance of ED, even with ideal and optimized operation.

Electro-driven technologies are viewed as a potential alternative to the current state-of-the-art technology, reverse osmosis, for the desalination of brackish waters. Capacitive deionization (CDI), based on the principle of electrosorption, has been intensively researched under the premise of being energy efficient. However, electrodialysis (ED), despite being a more mature electro-driven technology, has yet to be extensively compared to CDI in terms of energetic performance. In this study, we utilize Nernst–Planck based models for continuous flow ED and constant-current membrane capacitive deionization (MCDI) to systematically evaluate the energy consumption of the two processes. By ensuring equivalently sized ED and MCDI systemsin addition to using the same feed salinity, salt removal, water recovery, and productivity across the two technologiesenergy consumption is appropriately compared. We find that ED consumes less energy (has higher energy efficiency) than MCDI for all investigated conditions. Notably, our results indicate that the performance gap between ED and MCDI is substantial for typical brackish water desalination conditions (e.g., 3 g L–1 feed salinity, 0.5 g L–1 product water, 80% water recovery, and 15 L m–2 h–1 productivity), with the energy efficiency of ED often exceeding 30% and being nearly an order of magnitude greater than MCDI. We provide further insights into the inherent limitations of each technology by comparing their respective components of energy consumption, and explain why MCDI is unable to attain the performance of ED, even with ideal and optimized operation.

The potential of electrodialysis as a cost-effective alternative to reverse osmosis for brackish water desalination

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications.

Comparison of energy consumption in desalination by capacitive deionization and reverse osmosis

Correlation equation for evaluating energy consumption and process performance of brackish water desalination by electrodialysis

Side effects of antiscalants on biofouling of reverse osmosis membranes in brackish water desalination

Brackish water desalination using reverse osmosis and capacitive deionization at the water-energy nexus

This review aims to succinctly summarize recent advances of four key membrane processes (e.g., reverse osmosis (RO), forward osmosis (FO), electrodialysis (ED), and membrane distillation (MD)) in membrane materials and process designs, to elucidate the contributions of these advances to the steadfast growth of brackish water membrane desalination processes. With detailed analyses and discussions, the ultimate purpose of the review is to shed light on the future direction of brackish water desalination using membrane processes. Brackish water has widely varying particulate matter and boron contents, posing great risks of membrane fouling and excessive boron levels to the membrane desalination processes. Recent advances in these four membrane processes largely focus on improving fouling resistance, boron rejection, water flux, and energy efficiency. Aquaporin membranes and thin-film composite polyamide membranes incorporated with nanoparticles exhibit excellent performances for RO and FO, whereas super-hydrophobic membranes prove their great potentials for MD. While recent advances in RO and ED process designs are orientated towards membrane fouling prevention by exploring respectively novel energy-saving membrane-based pre-treatment and reversal operation, recent studies on FO and MD are centered on reducing the energy costs by advancing the fertilizer-drawn concept and utilizing waste heat. Membrane processes are dominating brackish water desalination, and this trend is hardly to change. Membranes based on nanoparticles and other novel materials are deemed the next membrane generation, and innovative membrane process designs have demonstrated great potentials for brackish water desalination. Nevertheless, further works are needed to scale up these novel membrane materials and designs.

Environmental Engineering ScienceVol. 19, No. 6 IntroductionMembrane Separations in Aquatic SystemsMenachem Elimelech and Mark R. WiesnerMenachem ElimelechSearch for more papers by this author and Mark R. WiesnerSearch for more papers by this authorPublished Online:6 Jul 2004https://doi.org/10.1089/109287502320963346AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail "Membrane Separations in Aquatic Systems." , 19(6), p. 341FiguresReferencesRelatedDetailsCited byEffect of branching in zwitterionic polymer brushes grafted from PES UF membrane surfaces via AGET-ATR(c)PJournal of Membrane Science, Vol. 672A study of inline chemical coagulation/precipitation-ceramic microfiltration and nanofiltration for reverse osmosis concentrate minimization and reuse in the textile industry5 October 2021 | Water Science and Technology, Vol. 84, No. 9Fabrication and characterization of high flux poly(vinylidene fluoride) electrospun nanofibrous membrane using amphiphilic polyethylene‐block‐poly(ethylene glycol) copolymer10 December 2020 | Journal of Applied Polymer Science, Vol. 138, No. 17Geothermal direct contact membrane distillation system for purifying brackish waterDesalination, Vol. 500Operating parameters optimization of combined UF/NF dual-membrane process for brackish water treatment and its application performance in municipal drinking water treatment plantJournal of Water Process Engineering, Vol. 38Recent Developments and Future Challenges of Hydrogels as Draw Solutes in Forward Osmosis Process3 March 2020 | Water, Vol. 12, No. 3Hierarchical fibrous microfiltration membranes by self-assembling DBS nanofibrils in solution-blown nanofibers1 January 2018 | Soft Matter, Vol. 14, No. 44A Novel Polyvinylidene Fluoride Tree-Like Nanofiber Membrane for Microfiltration19 August 2016 | Nanomaterials, Vol. 6, No. 8The effect of suspended matter concentration on the coagulation–flocculation and decantation process for low brackish water C (NaCl) = 3 g/L24 April 2015 | Desalination and Water Treatment, Vol. 57, No. 13Performance of reverse osmosis (RO) for water recovery from permeates of membrane bio-reactor (MBR)2 August 2013 | Desalination and Water Treatment, Vol. 52, No. 4-6Interfacially synthesized chlorine-resistant polyimide thin film composite (TFC) reverse osmosis (RO) membranesDesalination, Vol. 309Fouling in reverse osmosis (RO) membrane in water recovery from secondary effluent: a review25 February 2012 | Reviews in Environmental Science and Bio/Technology, Vol. 11, No. 2Influence of electrospun fiber size on the separation efficiency of thin film nanofiltration composite membraneJournal of Membrane Science, Vol. 392-393Characterization of bacterial population associated with a brackish water desalination membraneDesalination, Vol. 269, No. 1-3Using nanocomposite materials technology to understand and control reverse osmosis membrane compactionDesalination, Vol. 261, No. 3Modeling the effects of fouling on full-scale reverse osmosis processesJournal of Membrane Science, Vol. 314, No. 1-2Cake-Enhanced Concentration Polarization: A New Fouling Mechanism for Salt-Rejecting Membranes6 November 2003 | Environmental Science & Technology, Vol. 37, No. 24 Volume 19Issue 6Nov 2002 To cite this article:Menachem Elimelech and Mark R. Wiesner.Membrane Separations in Aquatic Systems.Environmental Engineering Science.Nov 2002.341-341.http://doi.org/10.1089/109287502320963346Published in Volume: 19 Issue 6: July 6, 2004PDF download

The desalination of brackish water provides water to tens of millions of people around the world, but current technologies deplete much needed nutrients from the water, which is determinantal to both public health and agriculture. A selective method for brackish water desalination, which retains the needed nutrients, is electrodialysis (ED) using monovalent-selective cation exchange membranes (MVS-CEMs). However, due to the trade-off between membrane selectivity and resistance, most MVS-CEMs demonstrate either high transport resistance or low selectivity, which increase energy consumption and hinder the use of such membranes for brackish water desalination by ED. Here, we introduce a new method for fabrication of MVS-CEMs, using molecular layer deposition (MLD) to coat CEMs with ultrathin, hybrid organic–inorganic, positively charged layers of alucone. Using MLD enabled us to precisely control and minimize the selective layer thickness, while the flexibility and nanoporosity of the alucone prevent cracking and delamination. Under conditions simulating brackish water desalination, the modified CEMs provides monovalent selectivity with negligible added resistance—thereby alleviating the selectivity–resistance trade-off. Addressing the water-energy nexus, MLD-coating enables selective brackish water desalination with minimal increase in energy consumption and opens a new path for tailoring membranes' surface properties.

Assessment of salt-free electrodialysis metathesis: A novel process for brine management in brackish water desalination using monovalent selective ion exchange membranes

A nanofibrous composite reverse osmosis (RO) membrane with a polyamide barrier layer containing interfacial water channels was fabricated on an electrospun nanofibrous substrate via an interfacial polymerization process. The RO membrane was employed for desalination of brackish water and exhibited enhanced permeation flux as well as rejection ratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium periodate systems and surface grafting with different alkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl, and octadecanyl groups. The chemical structure of the modified nanocellulose was verified subsequently by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and solid NMR measurements. Two monomers, trimesoyl chloride (TMC) and m-phenylenediamine (MPD), were employed to prepare a cross-linked polyamide matrix, i.e., the barrier layer of the RO membrane, which integrated with the alkyl groups-grafted nanocellulose to build up interfacial water channels via interfacial polymerization. The top and cross-sectional morphologies of the composite barrier layer were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to verify the integration structure of the nanofibrous composite containing water channels. The aggregation and distribution of water molecules in the nanofibrous composite RO membrane verified the existence of water channels, demonstrated by molecular dynamics (MD) simulations. The desalination performance of the nanofibrous composite RO membrane was conducted and compared with that of commercially available RO membranes in the processing of brackish water, where 3 times higher permeation flux and 99.1% rejection ratio against NaCl were accomplished. This indicated that the engineering of interfacial water channels in the barrier layer could substantially increase the permeation flux of the nanofibrous composite membrane while retaining the high rejection ratio as well, i.e., to break through the trade-off between permeation flux and rejection ratio. Antifouling properties, chlorine resistance, and long-term desalination performance were also demonstrated to evaluate the potential applications of the nanofibrous composite RO membrane; remarkable durability and robustness were achieved in addition to 3 times higher permeation flux and a higher rejection ratio against commercial RO membranes in brackish water desalination.

Performance evaluation of a brackish water reverse osmosis pilot-plant desalination process under different operating conditions: Experimental study

Experimental performance analysis for reverse osmosis pilot plant subjected to different brackish salinity spectrum