Applying constructed wetland-microbial electrochemical system to enhance NH removal at low temperature.

NH removal at low temperature (<10 °C) has baffled researchers and engineers for decades. Bioelectrochemical process has been increasingly valued as a promising approach to enhance NH removal by both electrochemical and stimulated microbial processes. The feasibility and the mechanism of enhanced NH removal were investigated in Constructed Wetland-Microbial Electrochemical System (CW-MES) with different electrode spacings including Constructed Wetland-Microbial Fuel Cell (CW-MFC) and Constructed Wetland-Microbial Electrolysis Cell (CW-MEC) at low temperature. Solar cell panel was firstly implemented in CW-MEC to enhance NH removal. The low-temperature operation lasted for about four months, CW-MEC successfully enhanced NH removal while CW-MFC did not exhibit positive effect. The NH-N removal efficiency of CW-MEC achieved 88.2 ± 7.0%, which was 11.7 ± 6.5% higher than conventional constructed wetland (CCW). The maximum NH-N removal efficiency of CW-MEC achieved 100%. The average NH-N mass removal rate was 436.02 mg m d. It was found that NH was mainly removed by the nitrification-autotrophic denitrification process in CW-MES while it was mainly converted to NO in CCW. Ammoxidation and denitrification were both enhanced by electricity while NH was used as the main substrate for electricity generation. AOA (Candidatus Nitrosocosmicus) and NOB (Nitrospira) were the main contributors to nitrification. This study provided a cost-effective and sustainable method for electrochemically enhanced microbial NH removal at low-temperature and revealed the relevant mechanism.