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

## TL;DR

A pilot system combining an iron–carbon anode and sand filtration effectively treated rural greywater for eight months, removing most contaminants but facing phosphorus removal challenges.

## Contribution

The study introduces a long-term field-tested integrated system for rural greywater treatment using an iron–carbon-enhanced microbial fuel cell and sand filtration.

## Key findings

- The system achieved over 90% removal of COD, TN, NH4+-N, SS, turbidity, and fecal coliforms.
- Microbial analysis showed Proteobacteria dominance in the cathode and Firmicutes enrichment in the anode.
- Phosphorus removal declined over time due to adsorption saturation.

## 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.

A pilot-scale iron–carbon enhanced constructed wetland-microbial fuel cell coupled with shallow sand filtration demonstrated stable, efficient removal of organics, nutrients and pathogens from rural greywater during long-term field operation.