Simultaneous removal of nitrate/nitrite and ammonia in a circular microbial electrolysis cell at low C/N ratios

In this study, the performance of a circular microbial electrolysis cell (MEC) system on removing NO3--N/NO2--N and NH4+-N at low C/N ratios was investigated. With the assistance of active bioelectrode, electron transportation and utilization efficiency between electron donor and acceptor was enhanced in MEC. High rate of nitrogen removal was observed in MEC at 0.2 V, which was 695.6 and 514.5 g-N/m(3)/d, respectively under COD/N = 2 and COD/N = 1. Without carbon source addition, the symbiotic activity of Anammox and electrochemical autotmphic denitrifiers were verified in MEC, in which the demand of NO2--N for NH4+-N removal is calculated to be similar to 1.3. Microbial community analysis revealed that the biocathode was enriched with autotmphic and heterotrophic nitrate/nitrite-reducing bacteria (e.g. 5.09 % Candidatus, 4.35 % Thauera and 3.34 % Comamonas), as well as the fermentative bacteria (e.g. 7.57 % Bacteroidetes). As heterotrophic denitrification, electroactive autotmphic denitrification, partial-denitrification and Anammox can coexist and collaborate in the MEC system, the strict nitritation to produce only nitrite toward Anammox can be avoided.