Onsite treatment of decentralized rural greywater by ecological seepage well (ESW)

Seepage well, as an ancient facility for sewage collection and treatment in China, still has reference significance for effective treatment of source-separated greywater in rural China under the background of rural revitalization. This study surveyed the discharge characteristic of rural greywater, and proposed onsite treatment of decentralized rural greywater using a novel ecological seepage well (ESW). In northwestern China, four rural households produced greywater with an average quantity of 128–146 L/d, with chemical oxygen demand (COD) of 213.6–235.9 mg/L as the main pollutant. For treating greywater, ESW with ceramsite and zeolite mixed in the packing layers and metallic corrugated plates (MCPs) set in the aeration zone achieved higher removal efficiencies of COD, total phosphorous (TP), total nitrogen (TN) and ammonia nitrogen (NH₄⁺-N). When the influent C/N ratio was 16, the enhanced removal performance was realized by cutoff duration of 9 h, and the effluent met the Chinese standard for irrigation water quality with COD, TP, TN and NH₄⁺-N removal efficiencies of 88.58%, 65.60%, 92.94% and 93.65%, respectively. Under the optimal condition, mechanism of pollutant removal by ESW was investigated. The variation of EPS and microbial morphology along the height illustrated that a micro-aerobic environment was formed in the lower layer of ESW. High throughput sequencing indicated plentiful denitrifying bacteria (DNB) and denitrifying phosphate accumulating organisms (DNPAOs), together with a higher relative abundance of ammonia oxidizing bacteria (AOB) than nitrite oxidizing bacteria (NOB) in the lower layer, which was relative to simultaneous nitrification, denitrification and phosphorous removal. This study provided theoretical and practical support for effective treatment mode of rural sewage.