Advanced treatment of decentralized sewage of new city development zones by two-stage anaerobic biofilter soil trench system

Due to the establishment of new development zones far from the urban core, non-point pollution has become a serious environmental issue. This wastewater may cause problems when it becomes connected to a central wastewater treatment plant (CWWTP) for cost reason. Therefore, decentralised wastewater treatment plant (DWWTP) is being paid more attention in China and other developing countries. In this study, a full-scale two-stage anaerobic biofilter soil trench system was designed and investigated for the treatment of wastewater from a new high school, with population of 1000-1200 people. The school is located eight kilometres from Wenzhou city, China. The aim was to evaluate the performance of an innovative soil trench system for small scale treatment of non-point pollution. During normal operation, this system showed a stable treatment performance. The removal efficiency of organic pollutants and suspended substance was high (CODcr: 89-96%; SS: 91-97%). Phosphorus removal was over 90% throughout the testing period (from 90% to 95%). Total nitrogen removal amounted to 68-75%, but high nitrification were observed at 96-99% removal of NH4+-N. Denitrification appears to be the limiting factor. It has been observed that the effluent quality of two-stage anaerobic biofilter soil trench system meet the discharge requirements of water pollution control regulation in China. Furthermore, the treated water can be reused for lawn watering and roads washing as reclaimed water.