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Zero discharge of wastewater, how far is the reality from the dream?

Public number: Maijishan Forum Source: Time: 2020-02-21 01:44:23

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   Last month, Li Shousheng, president of the China Petroleum and Chemical Industry Federation, and his party conducted a survey of wastewater treatment in the coal chemical industry in Shaanxi, and highly praised coal chemical companies for achieving near zero or even zero discharge of wastewater. How are these zero-emission projects operating? What are the successful experiences? How to resolve bottlenecks such as high operating costs and difficult disposal of biochemical sludge and crystalline salts? A reporter from China Chemical Industry Daily conducted an interview.

   

Each emission reduction process has its own characteristics  

"Our project of this size does not discharge any production waste water, and all kinds of waste water produced by the production unit are recycled to achieve zero waste water discharge." Said Li Wei, general manager of Shaanxi Yanchang China Coal Yulin Energy and Chemical Co., Ltd. The world's first comprehensive utilization of coal and oil and gas resources has been equipped with a zero wastewater discharge system. Through the multi-stage membrane separation and multi-effect evaporation and crystallization, major process technologies have been integrated and innovated to optimize operation. It has been operating stably for more than two years to achieve zero wastewater discharge. And the utilization of most of the salt resources has solved the problem of high-concentration brine treatment, and has opened a new way for the development of energy chemical industry in ecologically fragile areas.

At the production site of Yunenghua, the reporter could not see the sewage outlets and drying ponds common in chemical companies. According to He Changming, deputy director of the Shaanxi Petrochemical Research and Design Institute, which is responsible for the research and development system, the high-salt organic wastewater from the Yunenghua production system is subjected to ultrafiltration to remove particulate impurities, coagulation and clarification, and two-stage ion exchange, MBR biochemical Treatment and two-stage reverse osmosis concentration, of which 80% is recycled and reused, and the remaining 20% is recovered by a six-effect evaporation device at the end, and the mixed salt is crystallized and filtered.

Shaanxi Future Energy Chemical Co., Ltd. also achieved nearly zero discharge of wastewater. The company treats the high-concentration brine produced by the reuse water device, and then returns the clean water to the production system for recycling. The high-concentration brine produced by the reuse water device is discharged into the Hongdun Wastewater Treatment Plant in Yuyang District, which is operated in BOT mode. It adopts microfiltration + reverse osmosis + evaporation crystallization process, and the membrane concentration treatment capacity is 175 cubic meters / hour. Commissioning started in March last year. So far, the system has been operating stably.

 

Aiming at the industrial waste water produced in the process of coal pyrolysis and coal tar hydrogenation production with high oil content, high ammonia nitrogen, high organic matter, etc., Shaanxi Coal Chemical Shenmu Tianyuan Chemical Co., Ltd. adopts an independently developed extraction process and biochemical treatment, advanced treatment, DM membrane Recovery and evaporation crystallization and other technologies, to build a 1 million tons / year high-concentration organic wastewater treatment device, using pretreatment + biochemical treatment + advanced treatment three-stage treatment, effectively reducing tar, ammonia nitrogen, phenols, solid suspended solids, etc. in the wastewater, 70% of the reclaimed water is reused in the production system as circulating make-up water, and the rest is used for clean water to quench the coke, which not only realizes the recycling of water resources and zero discharge of wastewater, but also pioneers the clean production of blue carbon.

   

Many obstacles to industrialization promotion

The reporter learned in the survey that, although coal chemical companies and governments in the western region are increasingly demanding zero emissions, to achieve true zero emissions of wastewater, they face huge cost challenges. At the same time, there is no uniform standard and technical specification for zero wastewater discharge. Most zero discharge technologies have not departed from the traditional membrane concentration + simple evaporation mode, and the system's operation stability is not high, which has become a major obstacle to industrialization promotion and application.

 

Many companies have paid high costs to achieve the zero emission target. Dong Zhengqing, deputy general manager of Shaanxi Future Energy and Chemical Co., Ltd. said that the company's sewage treatment plant operated stably in 2016, with a wastewater treatment capacity of 6.736 million tons, a sewage treatment plant compliance rate of 100%, a reuse water unit compliance rate of 99%, and industrial water reuse The rate is 98.75%. The wastewater treatment and reuse water treatment operating costs are 4.646 yuan / ton and 2.297 yuan / ton, respectively.

 

Yunenghua's zero-discharge system has been in operation for more than two years, and the operating cost per ton of water is 15-20 yuan, which is much higher than the price of raw water. The Shenmu Tianyuan environmental protection facility investment is 746 million yuan, accounting for 35.7% of the total project investment. Among them, the investment of high-concentration organic wastewater treatment equipment was 410 million yuan. After trial operation in recent months, the wastewater treatment cost was estimated to be 39.86 yuan / ton.

 

"Zero emission of coal chemical industry is the development direction. These technologies also have their own advantages, but face the embarrassment of high costs. Only through technological breakthroughs to reduce costs can there be promotion value." Hu Haifeng, a member of the Shaanxi Provincial Decision Advisory Committee, told reporters that membrane concentration technology is For the fragile life of the reverse osmosis membrane, it can combine reverse osmosis and forward osmosis to concentrate high brine and then evaporate and crystallize, which brings hope for low-cost wastewater treatment. At the same time, the government should also give appropriate subsidies to encourage bold innovation .

        

"At present, there is no uniform standard for zero emissions. The rapid development of coal chemical industry in the northern region has a shortage of water resources. The environmental capacity of wastewater discharge is relatively small, which is more suitable for zero emissions. The environmental benefits are greater than the economic benefits." A responsible person told reporters that it is necessary to reduce the cost of wastewater treatment through technical research.

     

Biochemical sludge is extremely difficult to handle

The reporter of China Chemical Industry Daily also found that in addition to the high cost of zero discharge of coal chemical wastewater, the difficulty in disposing of the treated biochemical sludge and crystalline salt is also a common problem. Mixed salt may be classified as a hazardous waste and become a bottleneck.

"Biochemical sludge is not included in the" National Hazardous Waste List "(2016 edition), but local environmental protection departments require identification of biochemical sludge to determine whether it is a hazardous waste. Until the identification conclusion is determined, biochemical sludge can only be temporarily pressed. Hazardous waste management is temporarily stored in the warehouse, and it is difficult to select a qualified hazardous waste disposal unit for transfer and disposal, which is extremely difficult to handle. "Dong Zhengqing said that by analyzing and testing the crystalline salt of the sewage treatment plant, the metal content in the crystalline salt has not reached The standard for the identification of leaching toxicity of hazardous waste identification standards, but currently no hazardous waste identification unit is willing to undertake crystalline salt hazardous waste identification business. If crystalline salts are classified as hazardous waste, disposal costs will be higher.

 

Future Energy recommends that the state subsidize environmental protection facilities such as zero discharge of coal chemical wastewater, encourage companies to carry out research on biochemical sludge reduction technology, and relevant government departments should open up green channels and reduce approval procedures. At the same time, the company will broaden the disposal channels for crystalline salt, and allow the company to sell crystalline salt that meets applicable product quality standards as a by-product.


Qin Nu

 

Shenmu Tianyuan also called on the state to provide tax relief and special fund subsidies to hazardous waste disposal units and comprehensive resource utilization units; to support companies with large environmental investment and zero emissions.

 

It is reported that some companies are currently conducting research on the separation of miscellaneous salts, formulating product standards, and realizing standardized disposal or resource utilization.

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