Effects of different anode settings on the performance of nitrogen removal and electrogenesis capacity in constructed wetland-microbial fuel cells

Constructed wetland-microbial fuel cell (CW-MFC) coupling system is a combination of constructed wetland and bioelectrochemical technology, in which the anode is the key factor to limit the output power and pollutant purification performance of the coupling system. Two coupling systems, CW-MFC1 (without granular activated carbon) and CW-MFC2 (with granular activated carbon), were constructed to investigate the effects of the addition of granular activated carbon at the anode on the power generation and nitrogen removal performance of the coupling system. The compositions of microbial communities at the anode and cathode of the two systems were analyzed by high-throughput sequencing technology. The results showed that the output voltage and maximum power density (430 mV, 8.39 mW/m²) of the CW-MFC2 reactor were higher than those of CW-MFC1 (379 mV, 7.77 mW/m²). The ammonia nitrogen removal rate of the CW-MFC2 reactor was 65.72%±3.06% in the early stage of the experimental operation (days 0 to 29), which was significantly higher than that of CW-MFC1 (56.06%±3.71%), and the total nitrogen removal rates of the two were relatively close. On days 30 to 105, the ammonia nitrogen and total nitrogen removal rate of the CW-MFC1 reactor were gradually higher than that of CW-MFC2, especially the total nitrogen removal was more significant (CW-MFC1 42.69%±4.19%, CW-MFC2 32.50%±11.51%). Besides, the high-throughput sequencing results showed that the high abundance of Acinetobacter at the anode and plentiful denitrifying bacteria (Gemmobacter, Geobacter, Flavobacterium, Acinetobacter, and Dechloromonas, etc.) in CW-MFC1 might be the main reasons for the better denitrification performance of CW-MFC1 than CW-MFC2. Overall, adding granular activated carbon to the anode could improve the power generation performance of the CW-MFC coupling system, but it was not conducive to the biological nitrogen removal process.