Bioelectrochemical removal of nitrogenous co-contamination via graphene/polyaniline nanocomposite electrode

Bioelectrochemical system, which feeds microorganisms with green electrons to stimulate pollution bio-removal, has been regarded as a carbon-neutral approach for wastewater treatment. However, wastewater is usually complicated with two or more pollutants that has been rarely studied by bioelectrochemical treatment. Here, the bioelectrochemical removal of nitrate and nitrobenzene/azo dye co-contaminated wastewater were explored and augmented by applying graphene/polyaniline nanocomposite modified carbon paper electrode with a model electroactive bacterium, Shewanella loihica PV-4. It was found that removal rate of nitrobenzene was obviously decreased when adding nitrate as co-contamination in cathode, which was probably attributed to the inactivity of membrane-bund c -type cytochromes from bacteria death. Fortunately, sequential optimization improved bacteria survival rate to 90 %-98 % and fully removed co-contamination within 15 h. Notably, the sludge inoculated cathode showed approaching 100 % removal of 100 mg/L nitrobenzene and 1 mM nitrate within 24 h. Microbial community analysis revealed that functional bacteria such as Rhodocyclaceae with putative genes encoding cytochrome c and electron transport chain were enriched on electrode surface and determined the removal efficiency of co-contamination. This work not only explored the feasibility of co-contamination treatment via bioelectrochemical process but also inspired new ideas to deal with low carbon-to-nitrogen ratio wastewater.