Optimization of a baffled-reactor microbial fuel cell using autotrophic denitrifying bio-cathode for removing nitrogen and recovering electrical energy

•Investigating the performance of upward plug-flow baffled-reactor microbial fuel cell.•Autotrophic denitrifying biofilms successfully replaced abiotic catalysts for cathodic reaction.•Cathodic coulombic efficiency of 97.7 ± 1.9% was achieved.•Inhibition of the intermediate denitrifying compounds, nitrite, on denitrification was observed.

Microbial fuel cells (MFCs) gained emerging attention as an eco-friendly pathway for recovering electrical energy and treating wastewater. The electrochemical catalysis of cathodic reactions was one of the important issues for practical application of MFC technology. Here, it was disclosed the performance of a stake up-flow baffled-reactor MFC in which autotrophic denitrifying microorganisms catalyzed the cathodic reactions, reducing nitrate to nitrogen gas. The maximum power produced in this bio-electrochemical system (BES) was 15 ± 0.4 W m−3 NCV (net cathode volume) at an optimum cathodic nitrate loading rate (CNLR) of 150 g NO3−−N m−3 NCV d−1 using acetate as electron donor. A maximum of 76.5 ± 0.5 A m−3 NCV current and 97.7 ± 1.8% cathodic coulombic efficiency obtained at this CNLR. Autotrophic denitrification achieved on this bio-cathode was 148.3 ± 1.4 g N m−3 NCV d−1 utilizing biological anode. The efficiency of autotrophic denitrification and current generation of this BES was inhibited by the accumulation of denitrifying by-product, nitrite (NO2−), at concentrations beyond 3.59 ± 0.8 mgNO2−−N L−1 in the cathodic stream. The results demonstrated that this bio-cathode based baffled-reactor MFC had a good potential to eliminate abiotic cathodes and thus, made the system more economical and sustainable alternative for wastewater treatment, nitrogen removal and energy generation.