Perspective and Roadmap of Energy-Efficient Desalination Integrated with Nanomaterials

Evaluation of Electrodialysis Desalination Performance of Novel Bioinspired and Conventional Ion Exchange Membranes with Sodium Chloride Feed Solutions

Electrodialysis (ED) desalination performance of different conventional and laboratory-scale ion exchange membranes (IEMs) has been evaluated by many researchers, but most of these studies used their own sets of experimental parameters such as feed solution compositions and concentrations, superficial velocities of the process streams (diluate, concentrate, and electrode rinse), applied electrical voltages, and types of IEMs. Thus, direct comparison of ED desalination performance of different IEMs is virtually impossible. While the use of different conventional IEMs in ED has been reported, the use of bioinspired ion exchange membrane has not been reported yet. The goal of this study was to evaluate the ED desalination performance differences between novel laboratory‑scale bioinspired IEM and conventional IEMs by determining (i) limiting current density, (ii) current density, (iii) current efficiency, (iv) salinity reduction in diluate stream, (v) normalized specific energy consumption, and (vi) water flux by osmosis as a function of (a) initial concentration of NaCl feed solution (diluate and concentrate streams), (b) superficial velocity of feed solution, and (c) applied stack voltage per cell-pair of membranes. A laboratory‑scale single stage batch-recycle electrodialysis experimental apparatus was assembled with five cell‑pairs of IEMs with an active cross-sectional area of 7.84 cm2. In this study, seven combinations of IEMs (commercial and laboratory-made) were compared: (i) Neosepta AMX/CMX, (ii) PCA PCSA/PCSK, (iii) Fujifilm Type 1 AEM/CEM, (iv) SUEZ AR204SZRA/CR67HMR, (v) Ralex AMH-PES/CMH-PES, (vi) Neosepta AMX/Bare Polycarbonate membrane (Polycarb), and (vii) Neosepta AMX/Sandia novel bioinspired cation exchange membrane (SandiaCEM). ED desalination performance with the Sandia novel bioinspired cation exchange membrane (SandiaCEM) was found to be competitive with commercial Neosepta CMX cation exchange membrane.

Cerium oxide doped nanocomposite membranes for reverse osmosis desalination

Cerium oxide (CeO₂) nanoparticles (NPs) have indicated great potentials as nanofiller owing to its high surface area, antioxidant properties and low cost. In this paper, thin film nanocomposite (TFN) RO membranes were proposed to be prepared through incorporation of hydrophilic CeO₂ NPs in polyamide (PA) selective layers via interfacial polymerization (IP). EDX, XPS, SEM, AFM, contact angle and zeta potential were used to examine the property and morphology of the prepared membranes. CeO₂ NPs were successfully embedded in the PA network, which endowed the TFN membranes with rougher surfaces and thinner PA layers. The TFN membranes were fabricated with different CeO₂ NPs contents (0, 50, 100, 150, 200, 400 mg/L). With increasing CeO₂ NPs loading amount, the hydrophilicity improved from 85.4° to 65.7° and the surface charge declined from -19.4 to -34.2 mV. These characteristics contributed to a 50% enhancement in water flux of TFN-CeO₂100 membrane (containing 100 mg/L of CeO₂ NPs) without compromise the NaCl rejection (98%). Moreover, CeO₂ embedded membrane exhibited an enhanced fouling resistance property through preventing the adhesion of hydrophobic foultants. This study demonstrated the desirable applicability of CeO₂ NPs in synthesizing novel TFN membranes for desalination application.

Desalination Processes' Efficiency and Future Roadmap

For future sustainable seawater desalination, the importance of achieving better energy efficiency of the existing 19,500 commercial-scale desalination plants cannot be over emphasized. The major concern of the desalination industry is the inadequate approach to energy efficiency evaluation of diverse seawater desalination processes by omitting the grade of energy supplied. These conventional approaches would suffice if the efficacy comparison were to be conducted for the same energy input processes. The misconception of considering all derived energies as equivalent in the desalination industry has severe economic and environmental consequences. In the realms of the energy and desalination system planners, serious judgmental errors in the process selection of green installations are made unconsciously as the efficacy data are either flawed or inaccurate. Inferior efficacy technologies' implementation decisions were observed in many water-stressed countries that can burden a country's economy immediately with higher unit energy cost as well as cause more undesirable environmental effects on the surroundings. In this article, a standard primary energy-based thermodynamic framework is presented that addresses energy efficacy fairly and accurately. It shows clearly that a thermally driven process consumes 2.5-3% of standard primary energy (SPE) when combined with power plants. A standard universal performance ratio-based evaluation method has been proposed that showed all desalination processes performance varies from 10-14% of the thermodynamic limit. To achieve 2030 sustainability goals, innovative processes are required to meet 25-30% of the thermodynamic limit.