The difference between bioelectricity and direct current on the simultaneous removal of antibiotics and nitrogen in constructed wetlands

Given its advantages in terms of high efficiency and low energy consumption, bioelectrochemistry - integrated constructed wetlands (BEC-CWs) have been applied widely in the various pollutant removal. However, the study on the synchronous removal performance, difference and molecular mechanism of various pollutants in different BEC-CWs is limited. This study explored the difference of performance and mechanisms on the antibiotics and nitrogen simultaneous removal by microbial fuel cell - integrated CW (MFC-CW) and direct current - integrated CW (EC-CW). Results showed that MFC-CW and EC-CW were all performed better ofloxacin (OFLO) removal (>99 %), where the biodegradation was the key contributor (91.00–94.70 %). The MFC can better promote the substrate adsorption, while EC was more conducive to improve plant uptake for OFLO removal in CWs. MFC-CW (78.86 ± 11.61 %) performed better total nitrogen removal than EC-CW (58.84 ± 12.86 %). The anammox gene (107 ∼ 108 copies·g−1) played an important role in the nitrogen removal. The denitrification performance of BEC-CWs was inhibited due to OFLO addition, especially in EC-CW. MFC-CW inhibited the quinolone resistance genes generation and improved nitrogen removal efficiency by increasing the abundances of related microorganisms. The bioelectricity can improve the microbial diversity in CWs compared to direct current. The OFLO degradation in EC-CW were initiated with defluorination, dealkylation, decarboxylation, and opening of piperazinyl ring, while it was defluorination, dealkylation, and decarboxylation in MFC-CW. EC-CW tended to increase the membrane transport and signal transduction, while MFC tended to improve organic compound metabolism and nitrogen transformation. These findings provide new insights into the difference between bioelectricity and direct current on the synchronous removal of various pollutants in the constructed wetlands.