Enhanced water desalination efficiency in an air-cathode stacked microbial electrodeionization cell (SMEDIC)

• Ion exchange resins (IERs) between membranes improved desalination performance.
• Desalination rates for systems with IERs were 1.9–2.2 times those without IERs.
• Improved desalination extent was due to the reduction in membrane stack resistance.
• The use of IERs rather than spacers is useful even at high initial salt concentrations.

A microbial desalination cell was developed that contained a stack of membranes packed with ion exchange resins between the membranes to reduce ohmic resistances and improve performance. This new configuration, called a stacked microbial electro-deionization cell (SMEDIC), was compared to a control reactor (SMDC) lacking the resins. The SMEDIC+S reactors contained both a spacer and 1.4±0.2 mL of ion exchange resin (IER) per membrane channel, while the spacer was omitted in the SMEDIC-S reactors and so a larger volume of resin (2.4±0.2 mL) was used. The overall extent of desalination using the SMEDIC with a moderate (brackish water) salt concentration (13 g/L) was 90–94%, compared to only 60% for the SMDC after 7 fed-batch cycles of the anode. At a higher (seawater) salt concentration of 35 g/L, the extent of desalination reached 61–72% (after 10 cycles) for the SMEDIC, compared to 43% for the SMDC. The improved performance was shown to be due to the reduction in ohmic resistances, which were 130 Ω (SMEDIC-S) and 180 Ω (SMEDIC+S) at the high salt concentration, compared to 210 Ω without resin (SMDC). These results show that IERs can improve performance of stacked membranes for both moderate and high initial salt concentrations.