Abstract
A pilot-scale dual-chamber microbial electrolysis cell (MEC) equipped with a carbon gas-diffusion cathode was evaluated for H2O2 production using acetate medium as the electron donor. To assess the effect of cathodic pH on H2O2 yield, the MEC was tested with an anion exchange membrane (AEM) and a cation exchange membrane (CEM), respectively. The maximum current density reached 0.94–0.96 A/m2 in the MEC at applied voltage of 0.35–1.9 V, regardless of membranes. The highest H2O2 conversion efficiency was only 7.2 ± 0.09% for the CEM-MEC. This low conversion would be due to further H2O2 reduction to H2O on the cathode or H2O2 decomposition in bulk liquid. This low H2O2 conversion indicates that large-scale MECs are not ideal for production of concentrated H2O2 but could be useful for a sustainable in-situ oxidation process in wastewater treatment.
Highlights
Microbial electrochemical or electrolysis cells (MECs) are considered a potential sustainable platform for energy-efficient wastewater treatment, due to resource recovery and wastewater treatment
The peak current density was 0.94–0.96 A/m2 (0.47–0.48 A) during the experiments. This current density is much lower than $ 10 A/m2 in MECs fed with acetate medium, the enrichment procedure and inoculum used in this pilot was the same to our lab scale MECs showing $10 A/m2 [23]
The significant difference in this work is the size of the MEC is several orders of magnitude larger than lab scale MECs, which suggests the importance of anode-respiring bacteria (ARB) enrichment in full scale MECs
Summary
Microbial electrochemical or electrolysis cells (MECs) are considered a potential sustainable platform for energy-efficient wastewater treatment, due to resource recovery and wastewater treatment. Several studies have attempted pilot-scale MECs for either electricity or H2 production [3,4,5] to deploy MECs in field. None of these studies provided significant benefits of the recovered resource against input energy and materials. The recovered H2O2 from organic waste or wastewater can be used as an in-situ oxidant in wastewater treatment, improving the sustainability of wastewater management. Similar to a conventional MEC system, H2O2-producing MECs comprise of two chambers separated by an ion exchange membrane. The electrons flow through an external circuit to the cathode where oxygen is electrochemically reduced to H2O2 at the cathode surface by the two-electron pathway shown in Eq (1) below [11]: O2 + 2H+ + 2eÀ → H2O2
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