Enhancement of chromium removal and energy production simultaneously using iron scrap as anodic filling material with pyrite-based constructed wetland-microbial fuel cell

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Iron scraps was used as the anodic filling material coupled with pyrite as a substrate in a constructed wetland-microbial fuel cell (IsAno-PS) to investigate the power production and treatment of simulated wastewater that contained chromium. During 76 days of operation, the IsAno-PS facilitated the removal of total chromium, ammonia nitrogen, total phosphorus and energy production because of the synergetic effect between pyrite and iron scraps (p < 0.05). By XRD analysis and microbial composition analysis, chemical reduction (adsorption, complexation and reduction) and biological reduction were determined during the chromium removal reaction. According to alpha and beta diversity of microbial community composition in the system, the microbial community was significantly (p < 0.05) influenced by iron scraps. Electrically active bacteria like Firmicutes, were highly enriched, while the Fe (III)-reducing bacteria Geobacter and chromium-reducing bacteria Bacilli increased in the IsAno-PS. In network analysis, adding iron scraps was accompanied by distinct microbial communities, which could conductive to the bioremediation of chromium and participate in nitrogen cycle. Furthermore, Chloroflexi, which related to iron and sulfur cycling was identified as a module hub, implying taxa with low abundances can have important roles in ecosystem function. Iron scraps could affect the chromium removal by regulating the production of EPS. Chromate reductase (ChrR) gene decreased due to Fe2+ released by iron scraps. Overall, iron scraps used as the anodic filling material coupled with pyrite as a substrate in CW-MFCs could be an efficient configuration CW-MFC.