Wastewater treatment, energy recovery and desalination using a forward osmosis membrane in an air-cathode microbial osmotic fuel cell

A microbial osmotic fuel cell (MOFC) has a forward osmosis (FO) membrane situated between the electrodes that enable desalinated water recovery along with power generation. Previous designs have required aerating the cathode chamber water, offsetting the benefits of power generation by power consumption for aeration. An air-cathode MOFC design was developed here to improve energy recovery, and the performance of this new design was compared to conventional microbial fuel cells containing a cation (CEM) or anion exchange membrane (AEM). Internal resistance of the MOFC was reduced with the FO membrane compared to the ion exchange membranes, resulting in a higher maximum power production (43 W/m3) than that obtained with an AEM (40 W/m3) or CEM (23 W/m3). Acetate (carbon source) removal reached 90% in the MOFC; however, a small amount of acetate crossed the membrane to the catholyte. The initial water flux declined by 28% from cycle 1 to cycle 3 of operation but stabilized at 4.1 L/m2/h over the final three batch cycles. This decline in water flux was due to membrane fouling. Overall desalination of the draw (synthetic seawater) solution was 35%. These results substantially improve the prospects for simultaneous wastewater treatment and seawater desalination in the same reactor.

► A microbial osmotic fuel cell (MOFC) was developed that has an air cathode.
► The MOFC has a forward osmosis (FO) membrane between the electrodes.
► Power production was higher than MFCs with anion or cation exchange membranes.
► Stable water flux was established leading to efficient desalination.
► Fouling of the FO membrane needs to be minimized to improve performance.