Examination of inorganic-based draw solutes and mitigation of their reverse solute flux in osmotic microbial fuel cells

BACKGROUND: Osmotic microbial fuel cells (OsMFCs) integrate microbial fuel cell (MFC) and forward osmosis (FO) and can simultaneously achieve wastewater treatment, electricity generation and water recovery. The selection of appropriate draw solutes (DS) and reduction of reverse solute flux (RSF) are the key challenges for OsMFC operation. This study has examined ten inorganic-based DS and investigated the effect of electricity generation on the RSF. RESULTS: The OsMFC exhibited stable electricity generation with Na⁺-series and K⁺-series DS. For NH₄⁺-series DS, the ammonia-nitrogen loss percentage, which varied from 12.5 ± 0.4% to 47.7 ± 2.4%, was significant due to the high pH and aeration in the cathode. Inorganic scaling/precipitation was observed with Mg²⁺-series and Ca²⁺-series DS with DS loss percentage from 13.5 ± 2.8% to 28.0 ± 0.3%. Electricity generation could reduce the specific RSF by 70.3 ± 4.9% and 56.7 ± 13.4% for the Na⁺ and K⁺ DS, respectively. CONCLUSION: The Na⁺-series and K⁺-series DS was identified as the ideal DS for the OsMFC because of stable electricity generation and water flux and significant RSF reduction. NH₄⁺-series, Mg²⁺-series and Ca²⁺-series DS were not appropriate due to significant loss. Bioelectricity generation could reduce both RSF and specific RSF.