Enhanced fluoride removal in a novel magnesium-carbon micro-electrolysis constructed wetland through accelerated electron transport and anodic sacrifice

High fluoride (F⁻) content in the aquatic environment is a significant‌ issue affecting public health. Constructed wetlands (CWs) are believed to have unique potential for alleviating F⁻ pollution in the aquatic environment. In this study, magnesium (Mg) and iron/nitrogen co-doped biochar (FeNBC) was used as the filler of a novel micro-electrolysis constructed wetland (W_NME). Compared with the control, W_NME significantly enhanced the F⁻ removal efficiency from 19.1 ± 7.3 % to 54.1 ± 8.3 %, in which 90.7 % of total F⁻ removal in W_NME was attributed to the micro-electrolysis filler. The enhancement was attributed to the co-doping of iron and nitrogen, which improved the surface morphology, element distribution, and electrochemical performance of FeNBC. This led to an increase in the potential of FeNBC by 9.8 %, thereby increasing the potential difference within the Mg-C micro-electrolysis system. The Mg²⁺ release from anodic sacrifice in W_NME was promoted, which led to an increase in MgF₂ as the precipitate. Micro-electrolysis promoted the enrichment of electrochemically active bacteria in W_NME, resulting in enhanced electron transfer and high F⁻ removal efficiency. This study provided new insights for F⁻ removal in CWs and would shed light on the optimization of micro-electrolysis CWs for F⁻ removal from the aqueous phase.