Fate of sulfadiazine and its corresponding resistance genes in up-flow microbial fuel cell coupled constructed wetlands: Effects of circuit operation mode and hydraulic retention time

Few studies have evaluated sulfadiazine (SDZ) removal and the potential risks of antibiotic resistance gene (ARG) accumulation in up-flow microbial fuel cell coupled constructed wetlands (UCW-MFCs). This study aims to investigate the removal of SDZ, accumulation of ARGs (sulI, sulII, intI), and bacterial community changes in four UCW-MFC reactors with two hydraulic retention times (HRTs) and two circuit operation modes. The results indicated that effluent from a closed circuit UCW-MFC had a lower SDZ concentration due to a higher electrode absorption capacity for SDZ and the dehydrogenase activity of the bacteria. Additionally, the ARG abundance in closed circuit system was higher than that in open circuit system. A lower HRT was correlated with a higher SDZ concentration accumulation on the electrode, which led to a higher ARG abundance. Also, an obvious increase in the ARG abundance was observed during treatment periods. The relative abundance of target ARGs in the anode was higher than in the cathode and the bottom. A cluster analysis of bacterial communities at the phyla level showed they were more significantly affected by HRT. Furthermore, a closed circuit system and a high HRT contributed to high microbial diversity. In addition, five phyla of bacteria might be potential hosts for ARGs. Enrichment of ARG potential hosts induced by SDZ may be responsible for ARG abundance increase. Electricity production characteristics of the UCW-MFCs were also affected by HRT.