Qijiang Closed Mine Water Treatment Works, Chongqing (Five Passive-Treatment Stations)

Location: Qijiang District, Chongqing - five closed coal mines with excessive mine-water discharge, including the former Houxi mine in Anwen town. Qijiang is a traditional coal-producing district. After mine closures, several abandoned shafts kept discharging water carrying iron, manganese and other pollutants. A district survey found 13 closed mines still discharging; five exceeded pollutant limits and required dedicated treatment. Construction of five treatment stations began in April 2025. The stations use a passive train of cascade aeration, coagulation-sedimentation and oxidation-sedimentation, with no power drive and no full-time operators, cutting both energy demand and O&M cost at source. Each station comprises a diversion channel, a reaction-sedimentation tank and an ecological oxidation ditch, forming a closed natural purification loop: mine water leaves the adit and cascades down the channel for aeration, settles in the reaction tank, then passes through a terraced oxidation ditch where media filtration and plant-root uptake polish the water before it is discharged to the adjacent river. By the end of October 2025 all five stations had completed civil works and entered trial operation, where they remain while the authorities and the developer, Yunan Asset Management, track performance. A joint inspection at the former Houxi mine station confirmed that effluent sampling met all indices and the station was operating normally. The economics are the headline. Conventional mine-water treatment relies on mechanical equipment and chemical reagents at a cost of CNY 3-4 million per mine per year; the passive process cuts treatment cost by more than 90 percent, saving over CNY 20 million a year across the five stations. Effluent indices have remained stable and compliant, improving the district's water environment. Next steps include exploring reuse of the treated mine water, moving from compliant discharge to recycling, and codifying the approach as a replicable model for mining areas. Capacity per station, total investment, the applicable effluent standard and the handover date have not been disclosed and are not estimated here. Sources: "Chongqing Qijiang: passive process turns mine wastewater into living water", Xinhua - Chongqing Channel (source: Qijiang District Party Committee publicity department), 3 December 2025, http://www.cq.xinhuanet.com/20251203/8a8706cd0f664271a20163932b85c928/c.html; Chongqing Qijiang News, 2 December 2025, https://www.cqqjnews.cn/qijiang_Department/Department51/2025-12/02/content_4612966.htm Image: influent monitoring instruments (flow meters) at the former Houxi mine water treatment station in Anwen town, Qijiang, with staff checking operating data (trial operation; image source: Xinhua, photo by Wei Yuansen)