ObjectiveWith the development of the Zhijiang region, the wastewater volume in the region is expected to reach 130 000 m³/d in the near future and 160 000 m³/d in the long term. To meet the demand for wastewater treatment in the region, a new wastewater treatment plant (WWTP) needs to be built to receive 80 000 m³/d of wastewater in the near future (another 50 000 m³/d will be transported to the Qige WWTP through existing pipelines), and 160 000 m³/d of wastewater in the long term. At the same time, considering that the project is located in an important area of the Zhijiang Resort, with high land value and high environmental requirements, in order to minimize land use and eliminate the nimby effect, the project adopts a fully underground construction form.MethodsA new Hangzhou Zhijiang WWTP with a total capacity of 160 000 m³/d and a recent capacity of 80 000 m³/d will be constructed entirely underground. The wastewater treatment process adopts pre-treatment + pre-high-efficiency sedimentation tank + pre-denitrification biological filter + nitrification biological filter + post-denitrification biological filter + post-high-efficiency sedimentation tank + filter cloth filter + chlorination contact tank. The main pollutants COD, BOD₅, and TP emissions in the effluent will comply with the Class Ⅲ water quality standard of the Environmental Quality Standards for Surface Water (GB 3838—2002). Ammonia nitrogen will comply with the Class Ⅲ water quality standard (1.0 mg/L) of the Environmental Quality Standards for Surface Water (GB 3838—2002) from April to October each year, and comply with the Class Ⅳ water quality standard (1.5 mg/L) of the Environmental Quality Standards for Surface Water (GB 3838—2002) from November to March of the next year. SS of effluent is no more than 5 mg/L, TN of effluent is no more than 10 mg/L, all effluent indices are superior to the Class A standard of the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918—2002) The sludge treatment process includes mechanical concentration and dewatering + low temperature drying, and the sludge is transported out after the water content is no more than 45%.ResultsThe land occupation indicator per ton of water in the entire WWTP is only 0.18 m²/(m³·d), which is 1/5 of the national land occupation indicator for WWTP construction. The WWTP has been in operation for nearly a year, and the effluent can stably meet the designed standard. The effluent COD mass concentration is below 20.0 mg/L, with a removal rate of 93.3%; the effluent BOD₅ mass concentration is below 4.00 mg/L, with a removal rate of 97.3%; the effluent SS mass concentration is below 5.0 mg/L, with a removal rate of 97.5%; the effluent TN mass concentration is below 10.0 mg/L, with a removal rate of 75%; the effluent ammonia nitrogen mass concentration is below 1.00 mg/L, with a removal rate of 96.7%; the effluent TP mass concentration is below 0.20 mg/L, with a removal rate of 95%.ConclusionWhen the combined process of biological filter is used for secondary treatment, the effluent can stably meet the designed standards of effluent, and the occupied area is extremely small, making it suitable for engineering projects with high treatment requirements and limited land.