Effect of Cathodic Electron Acceptors on the Performance of Microbial Desalination Cell

Abstract

The effluent discharged from domestic and industrial activities contains both organic and inorganic matter, which requires effective treatment before discharging into the water body. Recently, a new bioelectrochemical system called microbial desalination cell (MDC) is developed for simultaneous removal of organic matter and dissolved solids along with energy recovery. Four MDCs, each consisting of five chambers, viz. anodic, cathodic, desalination, and two concentrate chambers, were operated in batch mode. The performance of MDCs for total dissolved solids (TDS) removal and power generation was observed using different cathodic electron acceptors, viz. oxygen, dichromate, permanganate, and hypochlorite. At 5 g/L of initial TDS concentration in desalination chamber, the TDS removal efficiencies of 52 ± 3, 55 ± 3, 58 ± 2 and 64 ± 2% were observed with oxygen, dichromate, permanganate and hypochlorite as catholyte, respectively. The TDS removal was further enhanced to 72 ± 2, 78 ± 4, 82 ± 3 and 89 ± 2% with oxygen, dichromate, permanganate and hypochlorite as catholyte, respectively, under 30 g/L of TDS concentration of saline water. Maximum sustainable power densities of 18, 26, 60 and 207 mW/m2 were generated with oxygen, dichromate, permanganate and hypochlorite as catholyte, respectively, at 100 Ω external resistance when 5 g/L TDS concentration was used for desalination. At 30 g/L of TDS concentration, the sustainable power densities increased to 25, 35, 84 and 347 mW/m2 with oxygen, dichromate, permanganate and hypochlorite as catholyte, respectively, due to reduced internal resistance of the cell. Hence, there is a scope to improve the electricity recovery in MDC using chemical catholytes. Higher TDS concentration in desalination chamber leads to higher desalination performance as compared to lower TDS concentration. High redox potential of hypochlorite favoured higher desalination performance as compared to other electron acceptors. Hence, cathodic electron acceptors have a significant effect on TDS removal and electricity recovery in the system.