Production of electricity and water in an osmotic microbial fuel cell by using EDTA-Na2 as a recoverable draw solute

Abstract

Osmotic microbial fuel cell (OsMFC) is an emerging biotechnology that integrates forward osmosis (FO) membrane into microbial fuel cells. Selection of an appropriate draw solute (DS) could affect both water extraction and electricity generation. Herein, we have investigated a promising DS - EDTA-Na2, a widely used chelating agent. The OsMFC with the EDTA DS achieved 779.6 ± 18.5C (electricity production) and 1.22 ± 0.02 LMH (water flux), both of which were comparable to that with the NaCl DS at the same conductivity. However, the EDTA DS resulted in a significantly lower reverse solute flux (RSF) of 0.36 ± 0.08 gMH and a lower catholyte pH that could ensure healthy operation of the tested FO membrane. The OsMFC with the EDTA DS exhibited a positive forward flux for Na+ ions, likely related to the effect of EDTA-Na complexion. Due to the lumping effects of EDTA dissociation equilibrium and membrane surface chemistry, a higher catholyte pH led to a higher water flux and reduced RSF, but lower electricity production. The cyclic voltammetry tests revealed that the reverse-fluxed EDTA species might have chelated FeII/III redox coupled to facilitate electron transfer on the anode surface, but the EDTA DS in the cathode could interfere with the cathodic reaction through assisting in metal wires oxidation. In the reuse test, >90% of EDTA DS could be recovered and then successfully reused in the subsequent OsMFC operation. The results of this study would encourage further exploration of using EDTA-based compounds as a draw solute for OsMFC applications.