The addition of iron-carbon enhances the removal of perfluoroalkyl acids (PFAAs) in constructed wetlands

Abstract

Hazardous perfluoroalkyl acids (PFAAs), particularly perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), have become ubiquitous environmental persistent organic contaminants, posing serious threats to environmental health, which has led to the development of PFAA treatment methods. Wetland construction in combination with iron-carbon (CW–I), a low-maintenance and high-efficiency technology, may be capable of removing PFAAs through physico-biochemical processes. In this study, we aim to investigate the removal efficiency of PFAAs by CW-I as well as the critical functions of all components within the wetlands. Pairwise comparisons of iron-carbon and control groups revealed that iron-carbon significantly enhanced 15.9% for PFOA and 17.9% for PFOS absorption through phytouptake and substrate adsorption, with respective removal efficiencies of 71.8% ± 1.03% and 85.8% ± 1.56%. The generated iron ions stimulated plant growth and further enhanced phytouptake of PFAAs, with PFAAs accumulated primarily in root tissues with limited translocation. Observations of batch adsorption suggest that chemical and electrostatic interactions are involved in the iron-carbon adsorption process, with film and intraparticle diffusions being the rate-limiting events. Fourier transform infrared spectrometer and X-ray photoelectron spectroscopy revealed that PFAA adsorption by substrates occurs at the molecular level, as well as the occurrence of hydrophobic force effects and ligand exchanges during the iron-carbon adsorption process. Additionally, iron-carbon significantly altered the genera, phyla, and community structure of microorganisms, and some microorganisms and their extracellular polymers may possess ability to bind PFAAs. The information provided in this study contributes to our understanding of the PFAA removal processes in CW-I and enriched the classical cases of PFAA removal by CWs.