This study presents the pareto-optimal design of a domestic point-of-use batch electrodialysis (ED) system. Specifically, the optimal geometry, flow-rates, and applied voltage for total cost minimization were explored for varying production rate (9–15 L/h) and product concentration (100–300 mg/L) requirements, while feed concentration and recovery ratio were maintained at 2000 mg/L and 90%, respectively. Capital cost dominated over energetic cost; hence, optimal designs maximized current density. Capital cost was significantly higher for 100 mg/L systems, than 200 and 300 mg/L: $141 vs. $93 and $79, at 12±0.5 L/h of production. Pumps were an important consideration, contributing up to 46% of the total cost. Large membrane length-to-width aspect ratios (3.5:1 to 6:1) and thin channels (0.30–0.33 mm) promoted high current densities, and 11–21 cm/s velocities optimized mass transfer against pressure drop. Optimal voltages were 0.9–1.3 V/cell-pair at 9 L/h, and decreased at higher rates. Lastly, higher production was obtained primarily by increasing cell-pair area rather than number of cell-pairs (36–46). It was additionally observed that active area increased linearly with feed concentration (1500–2500 mg/L), while recovery (60–90%) minimally affected design. This work also suggests that voltage control during the batch process, and less expensive pumps, can further reduce cost.
Bibliographical noteFunding Information:
This work was supported by the Tata Center for Technology and Design at MIT and Eureka Forbes Ltd. We also thank Professor Olivier L. de Weck for providing guidance and feedback on the optimization tasks.
© 2018 Elsevier B.V.
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