An oxic/anoxic-integrated and Fe/C micro-electrolysis-mediated vertical constructed wetland for decentralized low-carbon greywater treatment

The treatment of decentralized low-carbon greywater in rural area, particularly in cold weather, remains a challenge. Oxic/anoxic process and Fe/C micro-electrolysis were incorporated into vertical constructed wetland to develop ME-(O/A)CW for practical decentralized low-carbon greywater treatment. ME-(O/A)CW provided NH₄⁺-N, TN, TP and COD removal of 94.3%, 86.2%, 98.0% and 92.7%, respectively, at hydraulic loading rate of 0.9 m³/(m²·d) under low ambient temperature of −11.5 to 8.0 °C. Effective nitrification, phosphorus-accumulating and organic-degradation were proceeded in the aerobic layers and efficient H₂-/Fe²⁺-mediated autotrophic denitrification and Fe³⁺-based phosphorus immobilization were developed in the anaerobic layers through in-situ H₂-/Fe²⁺-supply by Fe/C micro-electrolysis. AOB (e.g. Nitrosomonadales), NOB/PAOs (e.g. Nitrospira), autotrophic denitrificans (e.g. Thiobacillus, Hydrogenophaga and Sulfurimonas), heterotrophic denitrificans (e.g. Denitratisoma) and Fe(II)-oxidizing bacteria (e.g. Ferritrophicum) dominated ME-(O/A)CW and confirmed the reaction mechanisms. The developed ME-(O/A)CW presented significant potential in the practical application for decentralized low-carbon greywater treatment under low ambient temperature.