The Hidden Journey of Power Plant Wastewater: From Waste to Wealth
While we enjoy the convenience brought by electricity, few people notice that power plants generate a large amount of wastewater during the power generation process. This wastewater has a complex composition, and direct discharge will cause severe damage to the aquatic ecosystem. However, through a scientific and rigorous treatment system, power plant wastewater can not only meet discharge standards but also realize resource reuse, completing the transformation from "wastewater" to "usable water".
I. Power Plant Wastewater: A Complex "Environmental Challenge"
Power plant wastewater comes from a wide range of sources. Especially represented by thermal power plants, the types of wastewater are quite diverse. They mainly include circulating cooling water discharge, acid-base regeneration wastewater from chemical water treatment systems, boiler ash and slag flushing wastewater, coal handling system flushing water, oily wastewater, and domestic wastewater in the plant area. The pollutants in different types of wastewater vary significantly, jointly forming treatment difficulties.
Among them, ash flushing water is one of the main pollution sources of thermal power plants, containing a large amount of suspended solids, fluoride, and often having a high pH value; acid-base wastewater comes from the resin regeneration process, requiring precise neutralization for acid-base imbalance; oily wastewater is rich in petroleum substances, which will form an oil film on the water surface if not properly treated; circulating water discharge accounts for more than 70% of the total wastewater discharge of thermal power plants, featuring large water volume, high salt content, and high hardness, making it a key target for resource reuse. If these pollutants enter natural water bodies, they will cause a series of problems such as water eutrophication, fish and shrimp death, and groundwater pollution.
II. Step-by-Step Purification: Power Plant Wastewater Treatment Processes
Power plant wastewater treatment follows the principle of "classified treatment and cascade utilization". According to the type of wastewater and pollutant characteristics, it adopts a combined process of pretreatment, biological treatment, advanced treatment, and terminal disposal to remove pollutants layer by layer and achieve water quality upgrading.
1. Pretreatment: Initial "Load Reduction" to Remove Large Impurities
Pretreatment is the first line of defense in wastewater purification, with the core goal of removing suspended particles, adjusting water quality and volume, and creating conditions for subsequent treatment. For wastewater with high suspended solids content such as ash flushing water and coal handling flushing water, sedimentation tanks, filter tanks and other facilities are used to allow particles to settle naturally or be retained by filter media. Qinling Power Plant adopts ash yard shafts combined with gravel filtration, which can reduce the suspended solids content of ash flushing water to below the discharge standard.
For acid-base wastewater, it first enters a neutralization tank, where acid-base agents are added to adjust the pH value to the neutral range; oily wastewater first passes through an oil separation tank to separate floating oil using the principle of oil-water stratification, and then enters an air flotation tank to remove emulsified oil, reducing interference to subsequent processes. In addition, all wastewater first enters an equalization tank to balance water quality fluctuations and water temperature, ensuring the stable operation of the treatment system.
2. Core Treatment: Precise Degradation to Tackle Key Pollutants
After pretreatment, wastewater needs to go through biological or chemical processes to degrade core pollutants such as organic matter, nitrogen, and phosphorus. The current mainstream biological treatment process is the combined "anaerobic + two-stage A/O + external MBR" process, which is suitable for treating power plant wastewater with high COD, nitrogen, and phosphorus content.
In the anaerobic reactor, anaerobic microorganisms decompose macromolecular organic matter into small molecules, and the biogas produced can be recovered and utilized, with a COD removal rate of 60%-80%; then it enters the two-stage A/O (anoxic/aerobic) system, where the first-stage A/O enhances denitrification, and the second-stage A/O further removes nitrogen and phosphorus. Through the metabolic activity of microorganisms, ammonia nitrogen and nitrate are converted into nitrogen gas for release, while residual organic matter is degraded; finally, through the external MBR (Membrane Bioreactor), ultrafiltration membranes are used to retain activated sludge and macromolecular substances, replacing traditional sedimentation tanks, which significantly increases sludge concentration and treatment efficiency.
For pH exceeding standard and fluoride pollution in ash flushing water, power plants also adopt special treatment technologies. For example, acid substances generated by biological oxidation of pyrite are used to neutralize high pH values, or aluminum sulfate and sodium bisulfate are used to adjust the pH to 7-8; in fluoride pollution treatment, the fly ash method is a model of "treating waste with waste", using fly ash produced by the power plant itself to adsorb fluoride ions, with a removal rate of over 90%, which not only reduces costs but also realizes waste utilization.
3. Advanced Treatment and Terminal Disposal: Towards "Zero Discharge" and Resource Utilization
Wastewater that needs to be reused or discharged in strict compliance with standards requires advanced treatment for further purification. Nanofiltration (NF) and Reverse Osmosis (RO) are core technologies: nanofiltration membranes can retain small-molecule organic matter and divalent ions to soften water quality; reverse osmosis membranes are like refined "molecular sieves", allowing only water molecules to pass through while retaining all dissolved salts and small-molecule impurities, realizing deep desalination.
For high-salt concentrated water, power plants adopt evaporation crystallization technology to realize salt resource utilization. The Mechanical Vapor Recompression (MVR) evaporation technology greatly reduces energy consumption by recovering secondary steam heat, and the crystallized sodium chloride and sodium sulfate have a purity of over 99%, meeting industrial salt standards. The more innovative flue gas atomization evaporation technology sprays concentrated water into the power plant flue in the form of mist, using flue gas waste heat to evaporate water, and the salt is captured by dust collectors, which not only achieves zero discharge of concentrated water but also reduces flue gas discharge temperature, killing two birds with one stone.
III. Turning Waste into Treasure: Environmental and Economic Value of Wastewater Treatment
Power plant wastewater treatment has long gone beyond the single goal of "meeting discharge standards" and moved towards a new stage of "resource recycling". The treated water can be reused in a cascade manner: water with poor quality is used for ash flushing, greening, and road cleaning; water after advanced treatment can be used as supplementary water for circulating cooling water, and even meet the standard of boiler feed water, significantly reducing the fresh water consumption of power plants. The full-process technology of Guodian Hanchuan Power Plant can produce 12,000 tons of industrial salt annually, saving 16 million yuan per year.
In terms of solid waste co-disposal, Guoneng Changzhou Power Plant has taken an innovative path. Through the "low-pressure steam drying + high-temperature incineration" technology, it disposes of 150,000 tons of municipal sludge annually, solving the problem of urban sludge disposal. At the same time, it reduces carbon dioxide emissions by 176,200 tons and saves 67,800 tons of standard coal, realizing the closed-loop utilization of "sludge-energy-building materials" and transforming the power plant from a "power producer" to an "urban environmental service provider".
IV. Future Trends: Low-Carbon and Intelligent Upgrading
With the advancement of the "dual carbon" goal and the tightening of environmental protection standards, power plant wastewater treatment is developing towards low-carbonization and intelligence. Photovoltaic-driven wastewater treatment systems can reduce power consumption by 30%, and microbial electrochemical systems can generate electricity while degrading organic matter; intelligent dosing systems based on digital twins can dynamically adjust the dosage of agents, reducing agent consumption by 18%; AI predictive maintenance can early warn of membrane fouling and extend the equipment operation cycle.
From wastewater discharge to recycling, from single treatment to coordinated governance, the iteration of power plant wastewater treatment technology demonstrates the determination of the energy industry for green transformation. Every drop of purified water not only protects the ecological environment but also builds a water resource circulation system of "water intake - water use - water treatment - reuse", injecting lasting power into the coordinated development of energy and the environment.
