Effects of number of cell pairs on the performance of microbial desalination cells

• Adding more cell pairs increases charge transfer efficiency in an MDC.
• Salt removal rate in mg h− 1 also increases with more CPs.
• More CPs result in more water loss and lower water recovery.
• Applying an external voltage can improve desalination and reduce operating time.
• Both water recovery and desalination performance should be evaluated for MDCs.

Microbial desalination cells (MDCs) are being developed as a low-energy desalination technology. Most MDCs in the previous studies contained one cell pair (CP, a pair of cation and anion exchange membranes) and very few had multiple CPs (< 5). The effect of the number of CPs on the MDC performance has not been well understood. Herein we examined the current generation, desalination, and water recovery in a bench-scale MDC containing up to 10 CPs, fed with salt water containing either 35 or 5 g L− 1 NaCl. It was found that current generation decreased with more CPs, while the charge transfer efficiency increased; the highest value of 450% was achieved with 10 CPs when treating 35 g L− 1, which also yielded the highest salt removal rate of 90.8 ± 8.3 mg h− 1. Applying an external voltage of 0.8 V greatly increased current generation and salt removal rate, and decreased the desalination time from 12 to 4 h. Water loss tended to be more serious and water recovery became lower with more CPs and/or lower salinity of the salt water. The results suggest that both desalination performance and water recovery should be evaluated when developing the MDC technology.

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