Long-term investigation of fouling of cation and anion exchange membranes in microbial desalination cells

The fouling of ion exchange membranes in microbial desalination cells (MDCs) was investigated through an eight-month operation. Multiple MDCs were set up by using cation (CEM), anion (AEM), and/or proton (Nafion) membranes. The MDCs exhibited relatively constant reduction of conductivity of artificial seawater during the testing period (46.3±6.3% in the CEM-MDC and 78.7±0.8% in the Nafion-MDC in an operating cycle). However, the current generation decreased from 99 to 56A/m3 in the CEM-MDC after 250days, and from 97 to 46A/m3 in the Nafion-MDC after 130days, indicating the presence of membrane fouling. Theoretically the MDCs removed 6.7–12.1kgTDS/m3/d with a high charge transfer efficiency of 230–440%, suggesting that electric current was not the only factor to drive desalination; water dilution played an important role in conductivity reduction as well. It was observed that the AEM contained significant biofouling, resulting from wastewater and microbial growth on organic compounds migrating across the membrane, while the CEM had substantial inorganic scaling, mainly consisting of calcium and magnesium. The membrane resistance of the CEM increased more significantly than that of the AEM, indicating that CEM needs more maintenance during MDC operation. [Display omitted] •Operation of microbial desalination cell (MDC) results in membrane fouling.•Biofouling dominates anion exchange membrane (AEM).•Inorganic scaling appears on cation exchange membrane (CEM).•The membrane resistance of CEM increases more significantly than AEM.