Operation adjustments of an electrochemically coupled system for total nitrogen removal and the associated mechanism

A coupled system consisting of sequencing batch reactor and microbial fuel cell (SBR-MFC) was designed to buffer pH drift and purify wastewater. The addition of nitrifying sludge and the adjustment of hydraulic retention time (HRT) were performed to achieve better removal of total nitrogen (TN). When anaerobic/aerobic/anoxic phases in one cycle were 6/4/2 h, the removal efficiency of ammonium was 99.0 +/- 1.3%, whereas denitrification was insufficient and the overall removal efficiency of TN was only 29.1 +/- 5.8%. When the phases were adjusted to 6/2/4 h, the removal efficiencies of ammonium were 100.0 +/- 0.0% in both closed and open circuits, and the overall removal efficiencies of TN were 91.4 +/- 0.2% and 71.7 +/- 4.2%, respectively, improved by 20% in MFC mode; the maximum voltage (200 Omega) maintained at 0.1 V. Ammonium-oxidizing bacteria (AOB) and Nitrite-oxidizing bacteria (NOB) in the sludge carried out nitrification. The main denitrification pathways in anoxic phase involved polyhydroxyalkanoate (PHA) denitrification by denitrifying glycogen accumulating organisms (GAOs) and electrochemical denitrification by electrochemical active bacteria (EAB). Few polyphosphate accumulating organisms (PAOs) were present, which accounted for poor P removal. (C) 2019 Elsevier Ltd. All rights reserved.