Enhanced energy recovery using a cascaded reverse electrodialysis stack for salinity gradient power generation

Sustainable energy harvesting and on-site disinfection of natural seawater using reverse electrodialysis

Seawater is a cost-effective and abundant electrolyte used as an electrode rinse solution to enable optimum utilization of reverse electrodialysis (RED). However, it is associated with several limitations, including the use of precious electrode materials, and its long-term stability must be addressed prior to its application in the field of seawater technology. In this context, a novel RED based on carbon electrodes was designed, and the experimental conditions were optimized for maximizing the harvesting of energy with aquaculture wastewater disinfection and recycling. The power obtained by RED, with a current density of 30 A/m² and a flow rate of 424 mL/min, designed by response surface methodology, was in good agreement with the predicted maximum power density (0.64 W/m²). The treatment was sustainable, mainly due to an anodic reaction of electro-generated sodium hypochlorite (NaOCl) under natural conditions, which afforded a high disinfection efficiency (above 99.5 ± 0.2% within 1 min under continuous flow (pH 8)), even under real seawater conditions and in aquaculture wastewater. Simultaneously, a stable power of 0.1 ± 0.03 W (0.25 ± 0.07 W/m²) generated a reasonable specific energy (within 0.02 kWh/m³). Inorganic fouling was efficiently suppressed using a surface-modified carbon cathode for 680 h. Thus, the on-site seawater disinfection by RED described herein is practically feasible and could offer a sustainable and energy-efficient alternative to seawater recycling.

Comparison of Physicochemical Properties of Two Types of Polyepichlorohydrin-Based Anion Exchange Membranes for Reverse Electrodialysis

The development of the most effective, suitable and economic ion-exchange membranes is crucial for reverse electrodialysis (RED)—the most widely studied process to harvest salinity gradient energy from mixing seawater and river water. RED utilizes two types of membranes as core elements, namely cation exchange membranes (CEM) and anion exchange membranes (AEM). Since the preparation of AEMs is more complex compared to CEMs, the design and development of anion exchange membranes have been the focus in this study. Homogeneous AEMs based on two types of polyepichlorohydrin (PECH) with different chlorine amounts (PECH-H, 37 wt% and PECH-C, 25 wt%) were synthesized, and first-time benchmarking of the membrane properties was conducted. In addition to physicochemical membrane properties, some instrumental analyses such as SEM, FTIR and DSC were investigated to characterize these anion-exchange membranes. Based on the results, although the PECH-H-type membrane had enhanced ion-exchange properties, PECH-C-based anion-exchange membranes exhibited a higher power density of 0.316 W/m2 in a lab-scale RED system. Evidently, there is room for the development of new types of PECH-C-based AEMs with great potential for energy generation in the RED process.