Bioelectricity drives transformation of nitrogen and perfluorooctanoic acid in constructed wetlands: Performances and mechanisms

Abstract

In this study, constructed wetland-microbial fuel cell (CW-MFC) filled with modified basalt fiber (MBF) via iron modification was utilized for treating perfluorooctanoic acid (PFOA) containing sewage. Results showed the significant promotion by bioelectricity on ammonium and total nitrogen by 7.80–8.14 %. Although such enhancement was suppressed by PFOA, higher removal was still observed with closed circuit, and PFOA removal also increased by 9.05 %. Bioelectricity contributed to enrichment of bacteria involved in nitrifying (Nitrospira and Ellin6067), denitrifying (like Thauera and Dechloromonas), iron redox (Geobacter), and sulfate-reducing (Desulfobacter), aligned with up-regulated of functional genes, including amoA, narG , napA, narK, narS, nrfA, sulp and sqr. Enrichment of autohydrogenotrophic and sulfide-oxidizing autotrophic denitrifiers, and nitrate dependent iron oxidation bacteria by bioelectricity all promoted denitrification. Moreover, bioelectricity boosted relative abundance of organic compounds degradation enzymes, such as dehydrogenase, decarboxylase, and dehalogenase, supporting the enhancement on PFOA removal. Generally, PFOA was converted to short-chain perfluorocarboxylic acids (PFCAs) via decarboxylation, hydroxylation, HF elimination, hydrolysis, F- elimination, C-C bond scission, and dehydration in CW-MFC. The final PFCAs-products determined was perfluorobutyric acid. This work estimated feasibility of treating PFOA containing sewage by CM-MFC, and offered new insights on enhancing mechanisms of nitrogen and PFOA conversion.