From Sewage Plant to Second Water Source: What Makes Reclaimed Water Projects Work

Three principles behind every treatment train

However many wastewater treatment technologies exist, their basic principles come down to separation, transformation and utilization. Separation uses technical means to strip suspended solids or colloidal particles out of the water so that pollutants fall to a minimum. Transformation applies to pollutants that are dissolved and either cannot or need not be taken out: biochemical, chemical or electrochemical methods convert them into harmless substances, or into substances that are easy to separate. Either way, treatment should push pollutants in a direction that favours control.

Four destinations for the water

Agricultural use is the largest reuse field, mostly crop irrigation governed by the Quality Standard for Agricultural Irrigation Water. Zhentou Village, Sandu Town, Jiande City, Zhejiang Province, adopted a graded treatment, graded utilization model for rural domestic wastewater and reached over 80% resource utilization: three-stage reuse at the front, middle and end sends treated water to farmland irrigation, orchard irrigation and greenbelt sprinkler irrigation, providing over 10,000 tons of water-fertilizer resources a year, saving about 1.5 tons of fertilizer and cutting electricity costs by more than 6,000 yuan. Ningxia Hui Autonomous Region has pursued reclaimed-water irrigation through a dedicated implementation plan.

The risks are documented, though. Sewage irrigation has left real damage: after more than 20 years of it, 2,500 hm2 of farmland in Shenyang's Zhangshi irrigation district was polluted with severe cadmium contamination, 5-7 mg/kg in paddy soil; near-suburban Tianjin saw 23,000 hm2 polluted; near-suburban Guangzhou polluted 2,700 hm2 by sewage irrigation and roughly 13,333 hm2 more by applying contaminated sludge, 46% of cultivated land. A mid-1980s survey of a Beijing sewage-irrigation district found about 60% of the soil and 36% of the brown rice polluted.

Environmental use covers river and lake replenishment and greenbelt irrigation, and ecological replenishment has become a major direction. In 2024 Beijing's river and lake replenishment used 1.182 billion m3 of reclaimed water, 70.5% of the city's total replenishment. Chengdu No. 9 Reclaimed Water Plant supplies ecological base flow to the Qingshui River and Xiaojia River Wetland, and the city's reclaimed-water utilization scale reached 1.25 million tons/day in 2024. Jinan Cuizhai Wastewater Treatment Plant, also called Capital Water, does similar work for dry-season river replenishment.

Industrial use, classified under GB/T 18919-202x Reuse of Urban Wastewater, covers cooling water, washing water, boiler and heating-network make-up water, process water and product water. In water-short regions reclaimed water has become the second water source, sometimes the first: Shanxi Province designated it the first water source for industrial production and requires high-water-consumption industries to prioritize it. Beijing's industrial reclaimed-water use reached 93 million m3 in 2024, over 30% of industrial water use. Huaibei City in Anhui built a full-chain production, distribution, application and management system and hit a 45% utilization rate, with industrial reclaimed-water use of 34.46 million m3 or 32% of the industrial total; Datang Huaibei Power Plant has used 180 million m3 since 2013. Keqiao District in Shaoxing, Zhejiang, put 380 million yuan into a 150,000-ton/day project that, since commissioning in 2023, has supplied 1.26 billion tons to over 270 enterprises in the Binhai Industrial Park and pushed the district's reuse rate above 28%, saving enterprises about 25 million yuan a year. Wuhai Thermal Power Plant in Inner Mongolia saves about 4.8 million m3 of groundwater annually. In high-end manufacturing, semiconductor production is the core ultrapure water scenario: at SEMICON China 2026, ultrapure-water preparation and recycling technologies were showcased with whole-plant water recovery rates up to 90%.

Municipal miscellaneous use covers construction, road sprinkling, car washing and toilet flushing. During construction of the Tianshan Shengli Tunnel, the world's longest highway tunnel, opened at the end of 2025, low-disturbance construction and wastewater reuse were used to protect the Tianshan ecological sensitive zone. Beijing replaced 3 million m2 of landscaping water with reclaimed water in 2024. Reclaimed water also heats and cools: Anyang City in Henan and Qingdao's Shibei District use reclaimed-water source heat pumps, with Qingdao having used about 3.254 million tons by the end of 2023.

The technology stack behind it

Reuse treatment builds on secondary treatment and improves water quality through advanced combined processes, membrane separation, ecological purification and smart management. Common advanced combinations include the pretreatment plus UF plus RO dual-membrane method used at the Dongying Chemical Park reclaimed-water project, and the A2O integrated oxidation ditch plus wetland purification plus UF/RO model used in Shandong Feicheng. Conventional advanced treatment, mechanical mixing, small-grid reaction tank, inclined-plate settler, Type-D filter and chlorination disinfection, is still widespread, for example at Ningbo Beilun Yandong WWTP.

Membrane separation is the core. Ultrafiltration separates particles and soluble matter, reverse osmosis performs deep desalination, and the MBR process integrates biological treatment with membrane separation for efficient solid-liquid separation, as at Jinan Cuizhai WWTP and Beijing Huaifang Reclaimed Water Plant. Ecological purification then polishes compliant effluent through constructed wetlands: Feicheng's Kanghui River Wetland and Anyang's tail-water wetland park rely on aquatic plants and microbes to adsorb and degrade residual pollutants. In industry, electrochemically enhanced descaling, membrane filtration concentration and collaborative treatment, such as feeding brewery wastewater to a WWTP as a biomass carbon source, achieve graded and cascaded reuse inside enterprises and parks.

The MBFB, or Membrane Biological Fluidized Bed, process goes further. On top of compliant discharge it reduces COD, NH3-N and turbidity through a biological fluidized bed and ceramic-membrane separation system, and the water can be reused directly or fed to RO desalination, replacing the long sand filtration, security filtration and UF train. Lower organics greatly extend RO membrane life and cut reuse cost. The inorganic ceramic membrane separation system is the world's first inorganic membrane separation system dedicated to wastewater treatment and, against other organic and inorganic membranes, offers high flux, backwashability and fully automatic operation.

Inside the MBFB reactor, powdered activated carbon (PAC) that has adsorbed large numbers of microbes becomes biological activated carbon (BAC). PAC then does several jobs at once: it adsorbs and enriches small-molecule organic pollutants, adsorbs and protects microbes, adsorbs dissolved oxygen, supports microbial decomposition under locally high pollutant and DO concentrations, and undergoes biological regeneration. Under intense fluidization, mixing, mass transfer and shear, PAC, microbes, DO and pollutants together break down micro-polluted small organics. The Di'er DECLEAN inorganic ceramic membrane system, developed by Seattle Environmental Technology (USA) and upgraded from ordinary ceramic-membrane research, reduces membrane fouling and greatly raises flux, overcoming the two biggest barriers to inorganic ceramic membranes in water treatment, high cost and low flux.

Benefits, and the friction that remains

The benefits are measurable on three axes. Economically, reuse directly cuts water costs: Keqiao saves enterprises 25 million yuan a year, Wuhai Thermal Power saves annual water fees, and Suining in Sichuan saves about 1 million yuan a year. Environmentally it cuts freshwater extraction and discharge: Feicheng's wastewater treatment plus wetland purification plus reclaimed-water recycling system will reduce groundwater extraction by 21 million tons a year at full operation, and Keqiao has cumulatively cut COD discharge by over 2,300 tons and total nitrogen by over 1,100 tons. Socially it builds a water recycling system and supports sustainable development, with a national target that by 2025 reclaimed-water utilization in water-short cities at prefecture level and above should exceed 25%, and in the Beijing-Tianjin-Hebei region exceed 35%.

Four frictions remain. Technology cost is high, processes are complex, and construction and operating capital needs are large. Public awareness and acceptance of reclaimed water are still insufficient. Policy support and standards systems need improvement, and market mechanisms and incentive policies are not yet sound. Supporting infrastructure, especially reclaimed-water pipelines, is difficult and costly to build in built-up areas.

The direction is clear enough. Reuse is moving toward refinement, intensification and digital-intelligence, with big data and AI building smart management platforms; application fields keep expanding from industrial cooling, municipal miscellaneous use and ecological replenishment into agricultural irrigation and regional recycling systems; and systematic planning across the whole chain, sewage collection, purification, ecological storage, distribution and use, is becoming the norm. The renaming from sewage treatment plant to water purification plant to reclaimed water plant reflects that shift from end-of-pipe treatment to resource recycling. Wuhai City is the extreme case: a 94% reclaimed-water utilization rate in 2023, nearly 25 million m3 collected and used, point-to-point delivery from its 2 municipal and 4 industrial-park WWTPs straight to enterprises, and 100% reclaimed water for circulating cooling in thermal power plants.