Enhanced removal of perfluorooctanoic acid and perfluorooctane sulphonic acid by direct current in iron-based constructed wetlands

Abstract

Iron minerals have been used for the treatment of PFOA and PFOS in constructed wetlands (CWs). Electron transfer that mediated by iron cycling is the primary mechanism for the removal of PFOA and PFOS. To further improve the electron transfer and enhance treatment efficiency of PFOA and PFOS, direct current with different voltages was applied in iron-based CWs. The results show that PFOA and PFOS removal efficiencies reached 63.2 ± 2.3 % and 57.5 ± 2.2 % at the voltage of 0.3 V, and further improved by 2.7 % and 3.5 % after the voltage increased to 0.8 V. The Cyt C that involved in electron transfer was increased to 174.9 ± 5.2 nmol/L in the cathode of voltage-added CWs. The contents of fulvic-like acids (18.2 %) and humic-like acids (9.5 %) materials that contribute to electron transfer were also 4.1 % and 2.6 % higher than that without direct current. The abundance of Geobacter that involved in electron transfer, PFOA and PFOS removal, was highly enriched in the application of direct current. Moreover, microbial pathways associated with PFOA and PFOS removal such as carbohydrate metabolism (sucrose metabolism), energy metabolism (oxidative phosphorylation), and membrane transfer (bacterial secretion system) were up-regulated. In general, the application of direct current showed excellent removal performance of PFAS through the enhanced electron transfer in iron minerals-based CWs.