Sustainable ammonia-contaminated wastewater treatment in heterotrophic nitrifying/denitrifying microbial fuel cell

Abstract

Abstract Air-cathode microbial fuel cells (ACMFCs) have a remarkable potential in wastewater treatment for scalable-scale and sustainable operation. In this study, a heterotrophic nitrifying/denitrifying air-cathode microbial fuel cell (HND-ACMFC) was investigated with ammonia-contaminated wastewater in long-term operation. Over an operational period of 197 d, high removal efficiencies of chemical oxygen demand (COD, 91%), ammonia (99%), and total nitrogen (TN, 95%) were achieved stably and repeatedly, with continuous bioelectricity production of 0.72 A/m3 and maximum power density of 100 mW/m3. Microbial community structure analysis showed that majority of the dominated bacteria were affiliated with Thauera, Nitrosomonas, Arcobacter, Pseudomonas, Clostridium, and Geobacter, which are identified as nitrogen-removing bacteria (NRB) and/or electrochemically active bacteria (EAB). Scanning electron microscopic analysis demonstrated the presence of a considerable number of bacteria attached to the two electrodes, even in the air-exposed part of the biocathode. Moreover, energy input/output evaluation showed that the maximum normalized energy recovery still reached 0.12–0.21 kWh/kg COD when ammonia nitrogen was depleted efficiently. These results demonstrate that HND-ACMFC is a possible approach to accomplish simultaneous wastewater treatment and energy recovery, and also enhances the activity of functional microorganisms. Hence, HND-ACMFC may benefit the sustainable treatment of ammonia-contaminated wastewater by using MFC technology in view of economical configuration/operation and high performance.