[Ocean Chemical News] my country’s coal chemical wastewater treatment technology route established

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The distribution of coal resources and water resources in my country is extremely uneven and reversely distributed. Water resources and water environment problems have become bottlenecks restricting the development of the coal chemical industry. In particular, the issuance and implementation of the "Ten Water Measures" have made this problem even more severe. To this end, my country has been committed to the development of "zero discharge" technology for coal chemical wastewater. Related research is gradually in-depth. The entire integrated technology has gradually matured, and the technical route of "pretreatment-biochemical treatment-advanced treatment-high salt water treatment" to achieve "zero discharge" of wastewater has been basically established. Pretreatment Pretreatment generally includes oil separation, acidification, precipitation, air flotation, sand filtration, solvent extraction, etc. Each method has its own advantages and disadvantages, and the solvent extraction method is currently mainly used. In the extraction method, complex extraction agents are gradually eliminated, and solvent extraction has recently emerged due to its advantage of not requiring acid and alkali reconciliation, and gradually occupied the market. Pretreatment should take targeted technical measures according to different water quality conditions. For example, the phenolic-containing acidic wastewater produced by the direct coal liquefaction project of Shenhua Group has high H2S, NH3 and phenol contents. Double-tower steam stripping and isopropyl ether extraction can make the concentrations of H2S, NH3 and phenol reach the range of biochemical treatment. Pretreatment can also remove or decompose macromolecular refractory organic matter in wastewater in advance. For example, n-octanol and cyclohexane are used as extraction agents to extract refractory organic matter in coking wastewater. The biodegradability of wastewater increases from 0.09 to 0.29, and the COD removal rate changes from 68.81% to 88.63%. Biochemical treatment Biochemical treatment generally adopts anoxic and aerobic biological treatment (A/O process) at home and abroad. However, due to the polycyclic and heterocyclic compounds in coal chemical wastewater, the COD index in the effluent after aerobic biological treatment is difficult to reach the standard stably. In order to solve the above problems, some new treatment methods have recently emerged, such as biochar method (PACT), biological fluidized bed treatment method (PAM), immobilized biotechnology, carrier fluidized bed biofilm method (CBR), anaerobic biological method, anaerobic-aerobic biological method, etc. The biochar method (PACT) can treat toxic and harmful organic pollutants that are difficult to biodegrade, and has good treatment effects on high-concentration macromolecular organic matter. ； The degradation efficiency of biological fluidized bed treatment method (PAM) is doubled compared with the suspended growth activated sludge process, and it also has strong nitrification ability to remove ammonia nitrogen. ； Immobilized biotechnology is a new technology developed in recent years. The domesticated dominant bacterial strains have a degradation ability of quinoline, isoquinoline, and pyridine that is 2 to 5 times higher than that of ordinary sludge, and its degradation rate of pyridine and other substances is more than 90%. Advanced treatment: Advanced treatment is to treat biochemical secondary effluent to make up for the limitations of biochemical treatment. It mainly includes coagulation and sedimentation, flocculation and sedimentation, multi-media filtration, activated carbon adsorption, membrane separation, and high-order oxidation and other transportation processes to ensure the quality of the effluent. The more commonly used advanced treatment technologies include electrocatalytic oxidation treatment. Other advanced treatment technologies include coagulation sedimentation, filtration, ozone oxidation, activated carbon filtration, and ultrafiltration. Taking crushed coal pressurized gasification wastewater as an example, biological combination technology is commonly used. Common advanced treatment methods include "ozone + BAF", "Fenton + contact oxidation", LAB, etc. BAF is the core process of current deep treatment. The "ozone + BAF" process combination is increasingly favored by new projects due to its reasonable process and good operating performance. High-salt water treatment wastewater is reused in the system after double-membrane treatment. The concentrated brine evaporates and crystallizes salt. Evaporation and crystallization are the main difficulties in the research and development of coal chemical wastewater treatment technology. Evaporators can generally increase the salt content in wastewater to more than 20%. The salt brine discharged from them is usually sent to evaporation ponds for natural evaporation and crystallization, or to crystallizers, where the crystals are dried into solids and transported to landfills for burial. Technical Difficulties The first few stages of coal chemical wastewater treatment technology are relatively mature. The current technical difficulties are mainly concentrated in the final evaporation crystallization and salt separation links. There are three main problems.: First, serious corrosion and fouling problems affect the continuous and stable operation of the evaporation device. Calcium, magnesium ions, sulfate ions, carbonate ions, silicates, etc. in the sewage produce calcium sulfate, calcium carbonate, etc. during the evaporation and crystallization process, which adhere to form a scale layer, which can easily block equipment and pipelines. ； Second, the operating cost is high. The steam consumption of multi-effect evaporation and the dosage of mechanical recompression process are the main consumption costs of the two technologies. ； Third, construction investment is large. Because concentrated salt water is highly corrosive at high temperatures, it requires high equipment and material selection, resulting in increased equipment and material costs. Development direction According to industry insiders, it is entirely possible to achieve zero discharge of coal chemical wastewater with existing technology regardless of cost. However, taking into account cost factors and the maturity of related technologies, the treatment process must be reasonably designed. It is necessary to choose which technology combination to use based on the effluent quality and site conditions, which process route to superimpose, and to use multiple methods to jointly treat coal chemical wastewater in sections. This is the basic development direction of coal chemical wastewater treatment technology. At the same time, coal chemical wastewater treatment needs to continue to develop unit technologies, such as front-end water treatment processes. It is necessary to find suitable process routes based on each water quality and reduce costs in a refined manner. ； The cost of the evaporation crystallization process accounts for a large proportion of the entire process, and there is an urgent need to develop a crystallization method suitable for high COD and high salt sewage in the coal chemical industry. ； We will do a good job in classifying salt by quality, developing the value of by-products, and reducing the cost of handling crystallized hazardous waste. (China Chemical Industry News)