1、 Typical process flow of reclaimed water reuse
The process of reclaimed water reuse needs to be adjusted according to the quality of raw water, reuse goals, and water volume. The common process can be divided into a three-level system of “pretreatment main treatment deep treatment”. The following are typical cases:
（1） Process of Domestic Sewage Reuse (Taking Urban Miscellaneous Water as an Example)
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Raw water (domestic sewage) → grid → regulating tank → biological treatment (such as A/O, MBR) → sedimentation/filtration → disinfection → reclaimed water reuse tank
Key link analysis:
Preprocessing:
Grille: intercepts large particles of impurities (such as tissues, suspended solids) to prevent subsequent equipment blockage.
Regulating pool: Balance water quality and quantity (domestic sewage water quality fluctuates greatly), creating stable conditions for subsequent treatment.
Main processing:
Biological treatment: Organic matter is degraded by activated sludge process or membrane bioreactor (MBR) (with a BOD removal rate of 80% -95%), and nitrogen and phosphorus are simultaneously removed (such as A ²/O process can make TN<15mg/L and TP<0.5mg/L).
Sedimentation/filtration: Remove suspended solids after biological treatment, commonly using sand filtration and fiber filter to achieve turbidity<5NTU.
Deep processing:
Disinfection: UV, sodium hypochlorite or ozone disinfection is used to kill bacteria and viruses (Escherichia coli count<3/L), meeting urban miscellaneous water standards.
（2） Industrial wastewater reuse process (taking high-purity water pretreatment in the electronics industry as an example)
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Industrial wastewater → pretreatment (neutralization, coagulation sedimentation) → membrane treatment (UF+RO) → ion exchange → high-purity water reuse
Key link analysis:
Preprocessing:
Neutralization: Adjust the pH to neutral (such as neutralizing acidic wastewater with alkali) to prevent corrosion of membrane components.
Coagulation precipitation: Add PAC/PAM to remove colloids and suspended solids, and reduce turbidity to below 1NTU.
Main processing:
Ultrafiltration (UF): intercepts large organic molecules and bacteria, protecting subsequent RO membranes (filtration accuracy of 0.01-0.1 μ m).
Reverse osmosis (RO): removes over 99% of dissolved salts and organic matter, resulting in a conductivity of less than 10 μ S/cm.
Deep processing:
Ion exchange: further removal of residual ions (such as Na ⁺, Cl ⁻) to meet the requirements of electronic grade high-purity water (conductivity<0.1 μ S/cm).
（3） Special water quality reuse process (such as printing and dyeing wastewater)
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Printing and dyeing wastewater → pretreatment (pH adjustment, decolorization) → anaerobic biological treatment → aerobic biological treatment → advanced oxidation (such as ozone/UV) → filtration → reuse
Characteristics: It is necessary to strengthen decolorization and organic matter removal (printing and dyeing wastewater contains dyes and surfactants), commonly using activated carbon adsorption or membrane separation technology to ensure chromaticity<30 times.
2、 The Importance of Reclaimed Water
（1） Relieve water scarcity
Data support: China’s per capita water resources are only 1/4 of the world average, and the water shortage rate in the northern region is 40%. Reclaimed water can replace 20% -30% of fresh water usage, for example:
The replacement rate of reclaimed water in urban greening and road flushing water can reach over 70% (mandatory in cities such as Beijing and Shenzhen).
In the industrial field, the reuse of cooling water in steel plants can save 60% of water, and the reuse rate of process water in chemical enterprises can reach 50%.
（2） Reduce environmental pollution load
Pollutant reduction: Direct discharge of untreated sewage can lead to eutrophication of water bodies (such as excessive TN and TP), while reuse of reclaimed water can reduce the discharge of pollutants such as COD and ammonia nitrogen. For example:
A 100000 ton/day reclaimed water plant can reduce COD emissions by approximately 15000 tons per year (calculated based on influent COD of 500mg/L and effluent COD of 50mg/L).
（3） Significant economic and social benefits
Cost advantage: The price of reclaimed water is usually one-third to one-half of that of tap water (such as 2.5 yuan/ton for Beijing reclaimed water and 5 yuan/ton for tap water). When the annual water consumption of large enterprises exceeds 1 million tons, reusing it can save millions of yuan in water bills.
Policy driven: The national “14th Five Year Plan” for the construction of a water-saving society requires that the utilization rate of urban recycled water reach over 25% by 2025, and cities such as Beijing, Shanghai, Guangzhou, and Shenzhen have introduced mandatory reuse policies.
3、 Scope of application for reclaimed water reuse
（1） Urban miscellaneous use areas
Typical cases of water quality requirements in application scenarios
Green irrigation with turbidity<10NTU and BOD ₅<20mg/L for park lawns and road green belts irrigation (with an annual water consumption of over 500000 tons in Beijing Olympic Park).
The suspended solids in road flushing are less than 50mg/L, and there is no obvious odor in the flushing of urban main roads and squares (Shenzhen consumes over 1 million tons of water annually).
The total number of bacteria in the flushing water is less than 100/mL, and there are no visible impurities in the toilets of office buildings and residential areas (50% of Singapore’s fresh water is used for municipal miscellaneous purposes).
（2） Industrial reuse field
Cooling water: Circulating cooling water for power plants and chemical plants (accounting for 60% -70% of industrial water consumption) is required to have a turbidity of less than 5NTU and a hardness of less than 300mg/L (calculated as CaCO3) to prevent equipment scaling.
Process water:
Textile printing and dyeing: The rinse water needs to be decolorized until the chromaticity is less than 50 times, COD＜100mg/L。
Electronics industry: The reuse of high-purity water requires a conductivity of less than 0.1 μ S/cm (for chip cleaning) and requires the combination of RO+EDI technology.
（3） Ecological and Agricultural Fields
Landscape water replenishment: Water replenishment for urban rivers, lakes, and artificial wetlands (such as 30% of the annual water replenishment for Suzhou moats being reclaimed water), with a requirement of TP<0.5mg/L to prevent algal blooms.
Agricultural irrigation: Irrigation of farmland in arid areas (controlling salt and heavy metals), such as using reclaimed water for irrigation in cotton producing areas in Xinjiang, can save 30% water, but it is necessary to ensure that Cd<0.01mg/L and Pb<0.1mg/L.
（4） Groundwater recharge
In areas with serious shortage of water resources (such as North China Plain), the reclaimed water after advanced treatment can be recharged to the groundwater aquifer to supplement the groundwater level (in accordance with the Technical Code for Groundwater Recharge Engineering (GB/T 19772-2005)).
4、 Typical case: NEWater in Singapore
Process: domestic sewage → microfiltration (MF) → reverse osmosis (RO) → ultraviolet disinfection, water quality meets drinking water standards (conductivity<10 μ S/cm).
Scope of reuse:
30% reinjection into the groundwater layer to prevent seawater backflow;
50% is used for industrial high-purity water (such as chip factories);
20% is further processed to become drinking water.
Meaning: Singapore’s self-sufficiency rate in water resources has increased from 50% in 1998 to 85% by 2025, making new water a core guarantee for national water security.
5、 Development Trends and Challenges
Technological upgrade: The application of MBR (membrane bioreactor), ozone biological activated carbon (O3 BAC) and other combined processes has increased, improving treatment efficiency and water quality stability.
Policy promotion: It is necessary to improve the water quality standards for reclaimed water (such as GB/T 18920-2020 “Urban Wastewater Reuse and Urban Miscellaneous Water Quality”) and establish a unified incentive mechanism for reuse.
Challenge: Industrial wastewater has complex components and high treatment costs (such as the cost of reusing electroplating wastewater reaching 10-20 yuan per ton of water), requiring further reduction of membrane technology costs and improvement of anti pollution capabilities.
The reuse of reclaimed water achieves the dual goals of “throttling” and “emission reduction” through “sewage resource utilization”, which is a strategic technology to solve the water resource crisis. In the future, its application in municipal, industrial, ecological and other fields will be more extensive.
Post time: Jul-04-2025