Views: 6 Author: Site Editor Publish Time: 2022-10-26 Origin: Site
Zero liquid discharge(ZLD) technology for industrial wastewater refers to the technology that separates the salts and pollutants from the industrial wastewater after treatment, and sends them to the solid waste disposal unit for treatment or recycling. The treated water can be reused to achieve no wastewater discharge. The increasingly tighter government regulations on the discharge of industrial wastewater due to the environmental effect make ZLD necessary when water is scarce or the local water bodies are protected by law.
Generally, the process of ZLD technology includes pretreatment, concentration and crystallization. The quality of wastewater produced by different industries varies greatly, and the treatment process of each segment should be selected according to the characteristics of each industry.
In order to meet the influent requirements of the subsequent concentration and crystallization process, the purposes of the pretreatment process include removing calcium ions and magnesium ions from the wastewater, and reducing the scaling and blockage of the evaporative crystallizer. In order to remove organic matter and silicon, and meet the requirements of the influent water quality of the subsequent membrane concentration system, the corresponding common process technologies are "two-alkali precipitation method + ceramic membrane filtration", "MBR+ resin softening", "advanced oxidation technology (ozone catalytic oxidation, photocatalytic oxidation)" and so on.
In order to reduce the investment and operation cost of the crystallization process, the concentration process can effectively reduce the processing capacity of the crystallization process. The commonly used process technologies are "ultrafiltration + reverse osmosis + high pressure reverse osmosis", "electrodialysis" and so on.
During the crystallization process, the salt in the concentrated water is mainly separated and reused in solid form or treated as solid waste. The crystallization process should be strictly selected according to the characteristics of the project. The commonly used process technologies are "enhanced evaporation (multi-effect evaporation, mechanical vapor recompression, etc.)", "membrane distillation (direct contact membrane distillation, sweeping gas membrane distillation, vacuum membrane distillation, etc.)" and so on.
In the last decades though, there has been an effort from the water treatment industry to revolutionize the high water recovery and ZLD technologies. Membrane technology has become one of the technologies that involved.