How can industrial wastewater MVR evaporators achieve zero-discharge treatment?

Zero discharge definition: After treatment, all pollutants in industrial wastewater are separated in the form of solids or concentrates, all treated water is reused, and there is no external discharge of waste liquid.

The core function of MVR evaporators is to completely separate water and pollutants from wastewater through efficient evaporation, concentration, and crystallization, making it a key terminal process for achieving zero emissions.

Process Flow Overview

1. Pretreatment Stage: Adjust pH, remove suspended solids, oils, and hardness ions (softening, coagulation, sedimentation, etc.) to prevent evaporator scaling and clogging.

   Advanced oxidation or biochemical treatment degrades some organic matter, improving wastewater evaporability.

2. MVR Evaporation and Concentration: Wastewater enters the MVR evaporator and evaporates at low temperature (typically 60-90℃) under vacuum. Water vaporizes, and the secondary steam is heated and pressurized by a compressor and recycled as a heat source.

   During evaporation, the wastewater is significantly concentrated, its volume is significantly reduced, and most of the water is recovered as steam condensate.

3. Crystallization and Solid-Liquid Separation: The concentrated liquid enters the crystallizer, where salts and other pollutants crystallize out by controlling temperature and concentration.

   The crystals are separated by a centrifuge and dryer, forming solid salts/mixed salts that can be disposed of or utilized as resources.

4. Condensate Reuse and Mother Liquor Treatment: The evaporation condensate is of high quality and can be directly reused in production or further treated with membrane technology before reuse.

   The mother liquor can be recycled for further concentration or treated separately, ultimately achieving zero wastewater discharge. 

Key Technologies and Advantages

1. Extreme Energy Saving and High-Efficiency Separation: MVR utilizes a vapor compression cycle, resulting in low energy consumption and high evaporation efficiency, making it suitable for the deep treatment of high-salt, high-COD wastewater.

2. Low-Temperature Operation and Automated Control: Low-temperature evaporation reduces the decomposition of heat-sensitive substances and equipment corrosion, while an intelligent control system ensures stable system operation.

3. Resource Recovery and Miscellaneous Salt Disposal: Valuable salts can be recovered, significantly reducing the amount of hazardous miscellaneous salts, some of which can be recycled, lowering disposal costs.

4. System Integration and Combined Processes: MVR is often combined with membrane processes and advanced oxidation methods to enhance overall treatment capacity and achieve high reuse rates and zero emissions.

5. Small Footprint and Stable Operation: High equipment integration makes it suitable for companies with limited space, and automated operation ensures long-term stability.

Practical Applications and Results

Typical Cases: In industries such as coal chemical, coking, printing and dyeing, and pharmaceuticals, wastewater treated by MVR evaporation and crystallization achieves a water reuse rate of over 95%, with only a small amount of solid salt transported for disposal or resource recovery, and no wastewater discharge. For example, a coking plant achieved zero wastewater discharge and recovered hundreds of thousands of tons of water resources annually through a "pretreatment + MVR evaporation and crystallization" process, realizing a win-win situation for both environmental protection and economic benefits.

V. Technical Challenges and Solutions

1. Inadequate pretreatment can easily lead to scaling and clogging, requiring enhanced front-end softening and filtration.

2. High-COD and complex wastewater requires optimized combined processes and rational segmented treatment.

3. The technology for resource recovery of mixed salts needs continuous improvement to reduce the pressure on hazardous waste disposal.

VI. Conclusion

Industrial wastewater MVR evaporators, through efficient evaporation concentration and crystallization separation, combined with pretreatment and intelligent control, can achieve complete separation of wastewater and water resource reuse, ultimately achieving the goal of zero discharge. It is a key technological equipment for modern industrial wastewater treatment, green transformation, and sustainable development.