Enhanced Removal of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) in Constructed Wetlands: Iron Cycling and Microbial Mechanisms

Perfluoroalkyl substances (PFAS) are persistent and ecotoxic chemicals in aquatic environments. To date, little is known about measures for strengthening PFAS removal in constructed wetlands (CWs). In this study, the role of iron oxide and iron-reducing bacteria (FeRB) in perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) removal was investigated in CWs. The removal efficiencies of PFOA and PFOS in the effluent were improved by 33.0 and 40.8%, respectively, in CWs with iron oxide and FeRB. The acetate as an intermediate product was also detected. The PFOS content was 86.7% lower at a substrate depth with poor oxygen. Almost 5.07% of PFOA and 24.6% of PFOS were absorbed by the substrate. Iron oxide increased the proportion of Proteobacteria, especially β-Proteobacteria. Increased proportions of genes that were related to iron reduction or oxidation, e.g., c-type cytochrome, reductase, and PilA, MtrC, MtrD, MshA, and FccA genes, were detected, which contributed to the iron cycle results. Meanwhile, the enhanced function of carbohydrate metabolism and greater proportions of genes involved in acetate decarboxylation (M00357; Methanosarcina and Methanothrix) played an important role in PFOA and PFOS removal. Given the increasing concerns related to PFAS, this study provides an effective and ecological in situ bioremediation method for PFAS removal.