“Breakthrough achieved in the treatment process of coal chemical industry wastewater using \"ED ion-exchange membrane concentration + crystallization for salt separation\"

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On September 12, a reporter from China Chemical Industry News learned during an interview with Inner Mongolia Yitai Coal-to-Oil Co., Ltd. that the pilot test of the crystal salt separation process for the \"zero discharge\" of coal chemical wastewater used by this company has been completed, with partial results achieved. It is reported that the final stage of achieving \"zero discharge\" for coal chemical industry wastewater is evaporation crystallization. The crystalline salts resulting from this process are classified as hazardous waste. The disposal of tens of thousands of tons of such hazardous waste each year imposes a heavy economic burden on enterprises, and it is also restricted by the capacity of local hazardous waste disposal facilities. At the same time, during the concentration and evaporation stage, conventional membrane concentration processes rely on high pressure to overcome osmotic pressure, resulting in high energy consumption, high operating costs, and high safety risks, which increase production costs and hinder the sustainable development of enterprises. The complete ‘zero discharge’ process route for coal chemical wastewater adopted by Yitai Coal-to-Oil Co., Ltd. has been fully verified and tested through on-site pilot tests as well as operational data from actual projects; it represents an effective approach to addressing the issue of coal chemical wastewater treatment. According to Chen Yegang, the inventor of this technology and chairman of Shanghai Dongshuo Environmental Protection Technology Co., Ltd., this process mainly includes: AOP advanced catalytic oxidation technology, ED ion-exchange membrane concentration technology, and crystallization salt separation technology. The AOP advanced catalytic oxidation process can remove over 50% of the COD in wastewater, and it plays a key role in further concentrating the wastewater and carrying out crystallization for salt separation. It prevents organic substances from affecting the concentration and evaporation-crystallization processes, thereby ensuring the feasibility of salt separation through crystallization. ED ion membrane technology combines ion membrane dialysis diffusion with electrochemical processes. By using a homogeneous, selectively permeable ion membrane, it enables the directed migration of ions under normal temperature and pressure driven by an external direct current field, resulting in high separation efficiency, a high concentration ratio, and high current efficiency. After concentration using ED ion exchange membranes, the TDS of the reverse osmosis concentrate can be increased from 30,000 mg/L to over 200,000 mg/L; the concentration factor is 4 times that of traditional processes. This greatly reduces the amount of water that enters the crystallization and salt separation stage. The electricity consumption per ton of water treated is less than 6 kW•h, thereby significantly reducing the energy consumption of systems aimed at achieving zero discharge of coal chemical wastewater. After concentration using ED ion-exchange membranes, the levels of major heavy metals in the two crystalline salts produced by the crystallization and salt separation process—sodium chloride and sodium sulfate—are all below the concentration limits specified in the criteria for identifying hazardous waste. This process achieves \"zero discharge\" of wastewater while enabling the recycling of crystalline salts, reducing the amount of hazardous waste to be disposed of by over 90% and significantly cutting the costs associated with hazardous waste disposal. At the same time, the scale of the subsequent evaporator treatment can be reduced by 75%, resulting in a reduction of overall investment by over 20%. With a significant reduction in the evaporation area, the system can save 60% on steam consumption and reduce operating energy costs by over 40%. At a national expert evaluation meeting held at the end of August under the auspices of the China Petroleum and Chemical Industry Federation, the advancement and breakthrough achievements of this process were unanimously recognized by the experts. The experts present believed that the crystallization and salt separation process for achieving \"zero discharge\" of coal chemical industry wastewater is theoretically feasible, with the key technical aspects properly addressed; it meets the conditions necessary for industrial implementation. This approach creates favorable conditions for truly achieving \"zero discharge\" of such wastewater, thereby laying a solid foundation for the sustainable development of the coal chemical industry. http://www.nmtech.com.cn/*nwen_mhg_xx.asp?id=172437