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The treatment of high salt wastewater is a worldwide problem. China produces more than 300 million cubic meters of wastewater per year. As a result, the high-salt waste generated by secondary production exceeded 10 million tons, and most of them were not properly disposed, which caused tremendous pressure on the ecological environment. In the interviews, industry experts generally believe that the current disposal of high-salt wastewater lacks economic and systematic treatment methods, and the by-products produced by the treatment are difficult to identify. Waste salt is often treated as hazardous waste, making it difficult to maximize economic value.

Missing core technology

It is reported that high-salt wastewater refers to wastewater containing organic matter, and its dissolved solids (TDS) has a mass fraction of at least 3.5%. Because in this type of wastewater, in addition to containing organic pollutants, it also contains a large amount of soluble inorganic salts. China's salty wastewater accounts for more than 5% of total wastewater production and is still growing at a certain rate.

Wu Gang, deputy director of the technical department of China Chemical Environmental Protection Association, said that high-salt wastewater mainly involves fine chemicals such as pesticides, dyes and pharmaceutical intermediates, as well as coal, chemical and oil refining industries. The high-salt wastewater components of pesticides, dyes and pharmaceutical intermediates are complex. It is difficult to handle. The problem of water pollution is particularly acute. Especially for characteristic pollutants, there has been a long-term lack of effective and economical treatment methods.

“In the field of high-concentration salty wastewater treatment, better applied technologies include membrane pretreatment technology, high-concentration salt-containing waste liquid incineration technology, and some enterprises adopt advanced combination technologies such as advanced oxidation and biochemical treatment. In the crystallization, mechanical vapor recompression (MVR) technology is commonly used, and biochemical treatment technology is used in the pretreatment stage. In recent years, the treatment of high-salt wastewater has received more and more attention, but in general, it is related to foreign developed countries. Compared with China's processing technology, there is still a certain gap, which is mainly reflected in the shortage of core technologies." Wu Gang said.

Zhuang Xiangning, director of the Environmental Protection Department of the Quality and Safety and Environmental Protection Department of the China Petrochemical Federation, also acknowledged that the high-salt wastewater is produced in large quantities, and most of them have no way out. At present, the technical support capacity is insufficient.

High cost

Zhang Ke, chief engineer of Tianjin Institute of Technology, said that there are many problems in the operation of high-salt wastewater treatment plants, the most prominent of which is cost. There are three reasons. First, the cost of wastewater treatment in the whole industry is high, and the cost of conventional and unit wastewater treatment methods is high, which is difficult to meet technical and economic requirements. Second, the problem of widespread dispersal and dispersion of processing technologies has not been analyzed and designed from the whole process of cleaner production, resource assessment, cost optimization, technology optimization, market optimization, and recycling industry. Third, most environmental companies and research institutions can only provide unit processes, lack system development and engineering capabilities, and cannot analyze and solve problems for users from the perspective of cost optimization.

Han Yuntao, general manager of Dalian Haiyi Heavy Industry Co., Ltd. said that the current mature technologies for treating high-concentration salt-containing organic wastewater include dilute biochemical method, evaporation concentration method, incineration method, membrane concentration method and catalytic oxidation method. Each treatment method has its advantages and disadvantages. For example, the dilution biochemical method considers the biodegradability of organic matter, which will generate a large amount of wastewater; the evaporation concentration method needs to be further processed after evaporation separation, which will increase the environmental protection cost of the enterprise.

An expert told reporters that if the cost is not considered, the "zero discharge" of the wastewater can be achieved, but after concentration and reuse, the remaining solid waste is difficult to handle. These solid wastes can be hazardous, difficult to landfill, difficult to handle, and expensive to handle.

By-product waste salt is difficult to use

Zhou Xianhui, deputy secretary-general of the China Petroleum and Chemical Industry Federation, said that the waste salt produced by the evaporation and crystallization of high-concentration salt-containing organic wastewater in the chemical industry exceeds 2 million tons per year. At present, waste salt is regarded as hazardous waste in many places and there is no way out. The amount of salt slag that caused the company to hoard.

Some companies also report that some low-risk waste salts are also treated as hazardous waste by local environmental protection departments due to lack of by-product identification and difficulty in identification, so they cannot be sold as products. At present, many projects have problems in extracting impurities from wastewater before they can be stacked. Since these impurities are recognized as hazardous waste, the treatment cost per ton should reach 3000-5000 yuan. Therefore, how to use these salt resources is one of our current research. direction.

Zhou Xianhui said that at present, Luxi, Shanghai chlor-alkali, Yangnong and other companies have had successful cases in the disposal of waste salt. They use polycarbon secondary salt production and mdi waste salt input membrane devices as raw material salts, or use membrane alkali plants to treat epoxy resin-containing salt wastewater, or organic phosphorus secondary salts to produce ionic membranes and soda. Other companies should also strengthen research on centralized disposal of waste salt.

In response to the technology needed in the future, Hu Qianlin proposed to promote comprehensive utilization and resource recovery technologies to achieve waste recycling and high-value utilization. The treatment of high-concentration salt mother liquor and waste salt should be based on harmlessness and resource utilization. Focus on. Encourage the use of catalytic oxidation, high temperature incineration, adsorption analysis, separation (crystallization) and other technologies, according to the standard production of by-product industrial salt; encourage the chlor-alkali, soda ash industry to make full use of its own brine purification, point dissolution, calcination and other equipment advantages, co-processing the production of other industries Waste salt, comprehensive utilization of salt resources; accelerate the demonstration and promotion of polycarbonate, epoxy resin and MDI waste salt in caustic soda production, explore the application technology of pesticide waste salt in ion-exchange membrane caustic soda and soda ash, and explore pesticide waste salt in ion Application techniques in membrane caustic soda and soda ash. In order to achieve natural circulation, “detoxification” treatment and drainage technology for salty wastewater were carried out in areas where conditions permit.