Impact of heterotrophic denitrification on BOD detection of the nitrate-containing wastewater using microbial fuel cell-based biosensors

Abstract

Microbial fuel cell (MFC)-based biosensors are promising alternative biochemical oxygen demand (BOD) detection method. However, the presence of alternative electron acceptor such as nitrate will interfere BOD detection because of the heterotrophic denitrification. So, it is essentially important to investigate how nitrate influences BOD detection and to make correction. In this work, standard BOD solution containing 20–500 mg/L BOD was used to evaluate performance of MFC biosensors impacted with 0–50 mg/L NO3−-N. Results demonstrated the underestimated BOD concentration detected using biosensors with impact of nitrate reduction. Graphical and mathematical method was proposed to make correction, and the corrected BOD concentration accurately indexing the organic matter concentration of the nitrate-containing sample could be obtained. Voltage output, polarization curve and cyclic voltammetry collectively suggested that denitrifying bacteria outcompeted over electricity-generating bacteria for electron donors, and that heterotrophic anodic denitrification was the priority process compared to current production. Generally, the more nitrate in standard solution, the more electron donors consumed for nitrate reduction and the less left for current production. The main nitrogen removal processes in MFC biosensors involved heterotrophic denitrification and ammonification at anode, ammonium transport to cathode chamber, and bioelectrochemical autotrophic denitrification at cathode. Phyla Bacteroidetes, Proteobacteria and Firmicutes were the dominant bacteria, accounting for more than 92% of the whole population in the anode chamber, while the phyla Bacteroidetes, Proteobacteria and Actinobacteria accounted for more than 84% in cathode chamber. The findings in this work provide important insights into BOD detection of nitrate-containing wastewater using MFC biosensors.