Biofilm-enhanced PFAS removal in constructed wetlands: Sewage sludge biochar drives adsorption and microbial synergy

Per- and polyfluoroalkyl substances (PFAS) pose significant risks to human health and ecosystems. Constructed wetlands (CWs), as a nature-based solution, are a promising and cost-effective approach for PFAS remediation. However, most studies have focused on plant uptake and substrate adsorption, neglecting the role of biofilms on CW substrates in PFAS removal. This study examines the differences in biofilms on functional (Sewage Sludge Biochar, SSB) and conventional (gravel) materials and their impact on the removal of perfluorobutane sulfonic acid (PFBS), a typical PFAS substitute. Experimental results show that the biofilm adsorption is the dominant way for PFBS removal in SSB-CW, as the SSB-biofilm adsorption capacity (809.0 ± 9.799 μg/g) significantly higher than that of SSB itself and the gravel-biofilm ( P  < 0.05). The high conductivity of SSB, attributed to its graphitic nitrogen content, facilitates the enrichment of electroactive microorganisms and regulates synergistic interactions between electroactive and non-electroactive microbial communities. This, in turn, modifies the biofilm structure and physicochemical properties, leading to increased zeta potential, enhanced hydrophobicity, and altered extracellular polymeric substance (EPS) composition. Consequently, these effects contribute to an improvement in PFBS removal efficiency, reaching 51.162 % ± 0.08. Undoubtedly, biofilms in CWs offer a promising approach for PFAS removal, where their adsorption capacity for PFBS can be regulated through material properties. This regulation reduces PFBS uptake by plants, thereby lowering environmental risks. Given the widespread occurrence of emerging contaminants in aquatic and terrestrial environments, this strategy provides valuable insights for PFAS remediation in surface water, groundwater, and soil systems.