Sustainable operation of osmotic microbial fuel cells through effective reproduction of polyelectrolyte draw solutes facilitated by cathodic pH increase

Osmotic microbial fuel cells (OsMFCs) take advantages of synergy between forward osmosis (FO) and microbial fuel cells (MFCs) for simultaneous wastewater treatment, bioenergy production, and water recovery. A unique feature for healthy operation of OsMFCs is an appropriate draw solute (DS) that can also act as a catholyte. Herein, polyelectrolytes (polyacrylic acid sodium salts, PAA-Na) was investigated as a DS/catholyte and reproduced with the aid of the high catholyte pH. Such a reproduction method is innovative, because it turns a drawback (high catholyte pH) into a useful resource, thereby reducing the demand for external input and leading to a clean production process. The results have showed that the OsMFC achieved a current density of 159 ± 6 A m⁻³, water flux of 12.7 ± 0.2 LMH, and low reverse salt flux of 0.05 ± 0.00 gMH with 32 wt% PAA-Na (2000 Da) as the DS. The DS recovery efficiency could be as high as 99.86 ± 0.04%, and the reproduced DS was successfully applied in the subsequent operation. With this reproduction method, the highest total operation cost was estimated at 0.104 $ m⁻³. Those results have demonstrated a new approach based on pH-dependent PAA DS reproduction towards further development of OsMFC technology for sustainable water/wastewater treatment and resource recovery.