Long-term performance and microbial insights of an iron–carbon enhanced CW-MFC and shallow sand filtration system for rural greywater treatment

Abstract

A pilot-scale integrated system combining an iron–carbon-enhanced anode constructed wetland-microbial fuel cell with shallow sand filtration (ICCW/MFC-SSF) was developed for decentralized rural greywater treatment. During an eight-month field trial, the system demonstrated robust and stable performance. It achieved high removal efficiencies for COD (92.3%), TN (82.6%), NH₄⁺-N (97.1%), SS (88.1%), turbidity (97.9%), and fecal coliforms (97.8%), with effluent meeting Chinese irrigation standards. The iron–carbon anode may have enhanced electron transfer and oxidative degradation, while the SS may have contributed to further nitrogen removal via reaeration. Dissolved organic matter (DOM) analysis revealed a shift from protein-like to refractory fulvic-like substances. Microbial community analysis indicated niche differentiation, with Proteobacteria dominant in the cathode and Firmicutes enriched in the anode. However, phosphorus removal declined over time due to adsorption saturation, highlighting a key limitation for long-term application.