Abstract:In response to the problems such as external water intrusion, influent concentration dilution, flood-period overflow, and effluent hard to meet the stringent standards of drainage basin caused by the combined rainwater and sewage from a county wastewater treatment plant (WWTP) in southwest China, the collaborative reconstruction project of “source separation in pipeline network + upgrading and capacity expansion of WWTP” is implemented. For the existing combined sewage pipelines and blind ditches in the old urban areas, the rainwater and sewage are separated and reconstructed, and the damaged sewage intercepting pipelines are excavated, replaced and repaired, the original 30 000 m3/d oxidation ditch process is upgraded to a “AAO + magnetic coagulation sedimentation + denitrifying filter” integrated process, and the treatment scale is expanded to 50 000 m3/d, which systematically optimizes the sewage collection and treatment efficiencies. The result shows that after the source reconstruction of pipeline network, the influent BOD? during flood period increases from 52.3 mg/L to 102 mg/L, and the C/N ratio rises from 1.41 to 3.68. The influent biochemical performance of WWTP is obviously improved. After the technological reconstruction, the effluent quality is enhanced from the Grade A standard in Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002) to the limiting values in Sichuan Provincial Discharge Standard for Water Pollutants in Minjiang and Tuojiang River Basins (DB51/2311—2016). In the economic operation, the unit treatment cost of sewage decreases by 12% with notable reductions in chemical consumption. This project demonstrates the effectiveness of the “plant-network integration” mode in improving quality and efficiency of small-sized and medium-sized municipal sewage systems, offering technical reference and practical experience for similar projects.
