Coking wastewater treatment

Now I will give some ideas.

Our company is building a sewage treatment plant and is in the design stage.

This post was last edited by cdpulin on 2009-9-22 10:25. There is no practical treatment, but I have done it for graduation project. The main issues are phenol content and oil. The general idea of ​​​​the design is to remove oil first, use extraction method to remove phenol, and then use A/O process for deep treatment.

summary: Based on the actual construction, operation and commissioning of the sewage treatment project of Benxi Beiying Iron and Steel Company, the process flow and principles of the coking wastewater AA/O system were introduced, and the factors affecting the sludge cultivation and acclimation during the commissioning and the nitrification and denitrification reactions were discussed. keywords: Coking wastewater nitrification-denitrification operation management 1 Introduction Coking wastewater is wastewater produced during the high-temperature carbonization of raw coal, gas purification and chemical product refining. There are three main sources.: The first is residual ammonia, which is wastewater produced during coal carbonization and gas cooling. Its water volume accounts for more than half of the total coking wastewater and is the main source of coking wastewater. ； The second is the waste water produced during the gas purification process, such as gas final cooling water and crude benzene separation water, etc. ； The third is wastewater generated during the refining process of tar, crude benzene, etc. and other occasions. Coking wastewater is industrial wastewater containing a large amount of refractory organic pollutants. Its composition is complex and contains a large amount of toxic and harmful substances such as phenol, cyanogen, benzene, and ammonia nitrogen. Coking wastewater discharged in excess of the standard causes serious pollution to the environment. At present, about 50% of domestic coking plants use the traditional aerobic sludge method to treat wastewater. Although the phenol, cyanide, and BOD5 in the effluent basically meet the emission standards, it has been difficult to meet the standards for ammonia nitrogen and onclick="g('COD');">CODcr. The coking and coking wastewater treatment system of Beiying Iron and Steel Group Coking Company uses the traditional activated sludge process, and its effluent onclick="g('COD');">CODcr and NH3-N seriously exceed the standards. When the company overhauled the coke oven in 2000, it also built a coking product recovery process and a phenol cyanide wastewater treatment station with a processing capacity of 70m3/h, using the A-A/O process to treat evaporated ammonia wastewater and other wastewater. After sludge cultivation, domestication, debugging and operation, the pollutants in the external drainage reached the secondary standard in the "Water Pollutant Discharge Standard for the Iron and Steel Industry" (GB13456-1992). 2 Water quality and process flow 2.1 Water quality of coking wastewater At present, the industrial wastewater of Bei Steel Group Coking Company mainly includes final cooling washing water, crude benzene separation water, residual ammonia water and other wastewater. These wastewaters are all collected together and sent to the ammonia evaporation tower to evaporate ammonia. The water volume is not large but the concentration of pollutants is very high. Specific indicators are shown in Table 1 Table 1 Treatment station inlet water indicator type Water quality/mg.l-1PH value Water volume/m3.h-1 Phenol cyanide onclick="g('COD');">CODCr Ammonia nitrogen inlet wastewater 120~200020~1004000~10000300~7005.5~9.025~45 The design value COD is basically stable at 200~300mg/l. 3.1.3 Domestication and cultivation of nitrifying bacteria and denitrifying bacteria. During the sludge cultivation process in anoxic and aerobic tanks, soda ash was used to adjust the pH of the incoming water to stabilize it between 7 and 8.5. As the sludge grew, the aeration volume was gradually increased to keep DO at 3 to 5 mg/l. After one month, bubbles began to form in the anoxic tank, and as the amount of return sewage increased, bubbles also increased. Tests on the inlet and outlet water quality of anoxic and aerobic pools also show that the removal rates of ammonia nitrogen and nitrate nitrogen are also gradually increasing. However, when the SV% of the aerobic pool increases to 25% and the MLSS is around 2.5g/l, due to insufficient air supply, the DO is significantly reduced, the bubbles in the anoxic pool are also significantly reduced, and the nitrification and denitrification effects become worse. 3.1.4 Debugging of the post-coagulation system First, static and dynamic tests were conducted on the polymeric ferric sulfate coagulant. The results showed that the best effect was achieved when the dosage was 100~300mg/l. Since part of the external drainage water from the secondary sedimentation tank is sent to the coke quenching tank for coke quenching, the amount of water entering the coagulation system fluctuates regularly. Therefore, the dosage of pesticides must be adjusted accordingly, otherwise the quality of the external drainage water will be affected. ； In addition, the coagulation sedimentation tank must be drained in time to prevent the concentration of suspended solids and COD in the effluent from increasing. 3.2 Influencing factors 3.2.1 Dissolved oxygen (DO) Nitrifying bacteria are obligate aerobic bacteria that oxidize NH3-N or NO2--N to obtain sufficient energy for growth. Therefore, the level of DO directly affects the growth and activity of nitrifying bacteria. When DO increases, the nitrification rate also increases. When DO is lower than 0.5 mg/l, the nitrification reaction tends to stop. The debugging results of coking wastewater show that the DO of the aerobic pool should be controlled at 3~5mg/l. The presence of oxygen will inhibit the reduction of nitrate by dissimilatory denitrifying bacteria, thus affecting whether denitrification can proceed to the end. There are reports that oxygen can inhibit the synthesis of nitrate reductase by some denitrifying bacteria. Oxygen can serve as an electron acceptor, thereby competitively hindering the reduction of nitrate. The denitrification rate reaches its maximum only when the DO in the environment is zero. ； As DO increases, the denitrification rate gradually approaches zero. The test results also show that the DO in the anoxic zone of the suspended sludge denitrification system should be controlled below 0.5 mg/l, while the DO in the biofilm denitrification system can be slightly higher and controlled below 1.0 mg/l. At present, the blowing system of the phenol cyanide treatment station operates two fans, and the air volume is seriously insufficient. Especially in summer, when the temperature rises, the fan performance decreases, resulting in the dissolved oxygen COD/TKN of the aerobic pool effluent being greater than 4, which is required to control the incoming water quality. When the BOD5/TN in the wastewater is greater than 3, the denitrification reaction can be carried out smoothly to achieve the purpose of nitrogen removal without the need for external carbon sources. When BOD5/TN is less than 3, additional carbon sources need to be added to achieve the ideal denitrification effect. The coking wastewater after ammonia evaporation basically meets the requirement that ('COD');">COD/NH3-N is greater than 6. 3.2.5 Sludge age Due to the limitation of dissolved oxygen, the sludge concentration has been maintained at 2~3g/l, and the corresponding sludge age is 10~15 days, which is lower than the ideal conditions of MLSS > 3g/l and sludge age greater than 50 days. 3.2.6 Control of Toxic and Harmful Substances Nitrifying bacteria grow slowly (generation time is about 31 hours), have low productivity, and recover slowly when the system load is impacted. ； Moreover, nitrifying bacteria are very sensitive to the presence of toxic substances. When the concentration of toxic and harmful substances exceeds a certain amount, it will inhibit the growth of nitrifying bacteria. Improper concentration control of volatile phenols, cyanide, ammonia, benzene, thiocyanide and NO2--N in coking wastewater can inhibit or poison nitrifying bacteria and denitrifying bacteria. After adding NaOH to the ammonia evaporation system to reduce ammonia nitrogen, the COD removal rate of the entire system was significantly improved. The COD removal rate of the aerobic tank was increased from the original 70% to more than 90%. After coagulation treatment, the COD of the system's external drainage onclick="g('COD');">COD reached less than 150 mg/l. 4． Conclusion 4.1 Beigang Group Coking Company uses the AA/O method to treat high-concentration wastewater after ammonia evaporation. onclick="g('COD');">COD and ammonia nitrogen removal rates are 96% and 86% respectively. The external drainage indicators can basically meet the GB13456-92 secondary emission standard. 4.2 The AA/O method is currently a more effective method for treating coking wastewater, but this method has poor resistance to load impact. The role of the accident adjustment pool in stabilizing system operation cannot be ignored and should be paid attention to in design and operation management. ； At the same time, coordination of various drainage processes should be strengthened to minimize fluctuations in system water quality. 4.3 Coagulation and sedimentation treatment plays an important role in ensuring the water quality of the entire system reaches standards, and can further reduce the CODcr concentration by 30~50%. 　　

This paper summarizes the water quality characteristics of coking wastewater, such as large volume, complex composition, and high pollutant concentration, as well as traditional coking wastewater treatment methods and their shortcomings, and proposes a new approach to treat coking wastewater using three-phase catalytic oxidation. The catalytic oxidation technology to treat coking wastewater was analyzed in terms of technical principles and processes, indicating that using this technology to treat coking wastewater is not only technically feasible, but also has good comprehensive benefits. Coking wastewater ； biological treatment ； Catalytic oxidation 1. Source and characteristics of coking wastewater 1. Source of wastewater During the coking production process, a large amount of wastewater containing phenol, cyanide, oil, ammonia nitrogen and other toxic and harmful substances is discharged. Coking wastewater mainly comes from the coking and gas purification processes and the refining process of chemical products, among which the remaining ammonia water generated during the helium evaporation process is the main source. Ammonia distillation wastewater is the wastewater discharged after distillation of mixed remaining ammonia water. The remaining ammonia water is the most important source of phenol cyanide wastewater in the coking plant. It is high-concentration phenol water containing ammonia. It is discharged by the circulating ammonia water pump in the condensation blast section and sent to the remaining ammonia water storage tank. The remaining ammonia water mainly consists of three parts: The wet water on the surface of the furnace coal, the combined water produced by the carbonization of the furnace coal, and the oily process wastewater added to the suction gas pipeline and the gas collecting pipe circulating oxygen water pump. The total remaining ammonia water can be installed with 14% of furnace coal. After the remaining ammonia water is mixed with the process wastewater sent from other production devices in the storage tank, it is called mixed remaining ammonia water. The destination of the remaining ammonia in the mixture is to directly evaporate ammonia, some to remove phenol first and then evaporate ammonia, some to combine with rich ammonia water to evaporate ammonia, and some to deselect ammonia together with rich desulfurization liquid. Before deacidification and evaporation of ammonia, filtration and oil removal are required. The coking plant also contains some other wastewater, which accounts for a small proportion and has low pollution indicators, so it will not be introduced here [1]. 2. Characteristics of wastewater: Coking wastewater contains pollutants including phenols, polycyclic aromatic compounds, and heterocyclic compounds containing nitrogen, oxygen, and sulfur. It is a typical industrial wastewater containing organic compounds that are difficult to degrade. The easily degradable organic compounds in coking wastewater are mainly phenolic compounds and benzene compounds. Pyrroles, naphthalenes, furans, and azoles are degradable organic compounds. Refractory organic compounds mainly include arsine, carbazole, biphenyl, terphenyl, etc. The quality of coking wastewater varies greatly due to the vast differences in the process flow and production operations of each plant. The quality of ammonia evaporated wastewater in general coking plants is as follows:: CODcr3000-3800mg/L, phenol 600-900mg/L, cyanide 100mg/L, oil 50-70mg/L, ammonia nitrogen 300mg/L or so. If CODcr is calculated as mg/L and ammonia nitrogen is calculated as 280 mg/L, then each ton of coke can produce at least 0.65kg CODcr and 0.05kg ammonia nitrogen. The national machine coke production is 70 million tons, so 45,500 tons of CODcr and 3,500 tons of ammonia nitrogen can be produced every year. If the sewage is not treated, how much pollution will be caused to the environment [1]. In general, coking wastewater has the characteristics of complex composition, toxic and difficult to degrade, high organic matter content, high ammonia nitrogen concentration, and large changes in water quality and quantity. Therefore, the removal efficiency of ordinary physical and chemical methods and biochemical methods is low, and the effluent does not meet the standards. Therefore, the key to treating this wastewater is to choose effective treatment methods. 2. Traditional treatment methods of coking wastewater and their shortcomings The traditional treatment methods are mainly active pollution methods, as well as physical and chemical methods such as coagulation. In the activated sludge process, most of the biological adsorption regeneration processes using forced aeration are used [2]. The typical process flow is shown in Figure 1: Production wastewater evaporated ammonia oil removal tank regulating tank flotation tank ammonia water treatment wastewater discharge coagulation sedimentation tank sludge sedimentation tank biochemical aeration tank sludge sent to the coal yard return sludge air Figure 1 The practice of the biological treatment process of coking wastewater shows that although the activated sludge method can remove most phenols and cyanogens, the removal effect of COD and refractory organic matter such as apyrrole, naphthalene, furan, pyridine, apyridine, carbazole, biphenyl, terphenyl, etc. is not satisfactory, and the effluent is difficult to meet the discharge standards. In order to improve the quality of effluent water, many domestic coking plants adopt delayed aeration treatment methods. Although delayed aeration can improve the removal rate of easily degradable substances such as phenols, the removal effect of refractory substances such as quinoline, isoquinoline, indole, pyridine, and dibenzoate is not ideal. According to research by Zhang Xiaojian and He Miao [3, 4], when the inlet water COD is 1300 mg/L and the hydraulic retention time of the aeration tank is 72 hours, the effluent COD is still 246 mg/L. ； This shows that coking wastewater contains a large amount of refractory substances, and the discharge standards cannot be met by simply increasing the aeration time. At present, domestic large and medium-sized coking plants are unable to achieve * * Regarding CODcr emission standards, in order to reduce CODcr to less than 100 mg/L, enhanced microbial methods are often used, such as adding iron salt or activated carbon to the aeration tank. Although adding iron salt can improve the COD removal rate, it increases the amount of sludge discharge and causes sludge treatment problems. The activated carbon adsorption method can achieve a high COD removal rate, but activated carbon itself is expensive. In actual operation, the loss of activated carbon regeneration exceeds 10% each time, which increases the cost of treating wastewater [5]. 3. Analysis of catalytic oxidation treatment of coked wastewater 1. Principle analysis The principle of new high-efficiency catalytic oxidation is to use a strong oxidant - chlorine dioxide to catalytically oxidize organic pollutants in wastewater under normal temperature and pressure in the presence of surface catalysts, or directly oxidize organic pollutants, or oxidize large molecular organic pollutants into small molecular organic pollutants, improve the biodegradability of wastewater, and better remove organic pollutants. In the process of degrading COD, it breaks the double-bonded chromophores in organic molecules, such as azo groups, nitro groups, sulfide hydroxyl groups, carboimino groups, etc., to achieve the purpose of decolorization, while effectively increasing the BOD/COD value, making it easy to biochemically degrade. In this way, the chlorine dioxide catalytic oxidation reaction acts as a bridge between conventional physical and chemical pretreatment and biochemical treatment in high-concentration, high-toxicity, high-salt wastewater. The core of this technology is three-phase catalytic oxidation. These three phases are: The compressed air (gas phase) sent into the tower by the fan, the high-efficiency oxidant (liquid phase) produced by the agent generator, and the catalyst (solid phase) fixed on the carrier. The catalyst is a composite precious metal compound developed by us. It is the role of the catalyst that makes the oxygen in the air also participate in the reaction as an oxidant, thus reducing the consumption of liquid phase oxidant, lowering the treatment cost, improving the treatment efficiency, and increasing the reaction speed. * * Speed ​​up and shorten the residence time of wastewater in the tower. After the wastewater is pretreated to remove impurities in the water, it enters the catalytic oxidation tower. The organic pollutants in the water are decomposed by the oxidant under the action of the catalyst. The benzene ring and heterocyclic organic matter are ring-opened and chain-broken, and the large molecules are turned into small molecules. The small molecules are further oxidized into carbon dioxide and water, thereby greatly reducing the COD value in the wastewater and basically fading the color. At the same time, the ratio of BOD/COD is increased, the toxicity of the wastewater is reduced, the biodegradability of the wastewater is improved, and conditions are created for subsequent biochemical treatment, so that the wastewater can meet the discharge standards after treatment. 2. Description of the oxidizing agent chlorine dioxide. Chlorine dioxide (CLO2), with a molecular weight of 67.46, is one of the few compounds that exists completely or almost completely in the form of monomer free atomic groups in nature. It is a yellow-green or orange-red gas at room temperature. CLO2 vapor looks and tastes exactly like chlorine and has a suffocating smell. Chlorine dioxide is unstable and cannot be heated when heated. It decomposes into oxygen and chlorine when exposed to light and is easily soluble in water. Its solubility is about 5 times that of chlorine. CL- in chlorine dioxide exists with a positive tetravalent valence and can accept 5 electrons. Its electrode potential E0=1.95V is second only to ozone (E0=2.07). It is a strong oxidant. Its available chlorine is 2.6 times that of chlorine. It can react violently with many substances [6]. Chlorine dioxide quickly decomposes when it meets water to generate a variety of strong oxidants, such as HCLO3, HCLO2, CL2, H2O2, etc., and can produce a variety of active free radicals (i.e., free radicals) with extremely strong oxidizing ability. These free radicals can excite active hydrogen in organic molecules and generate R through dehydrogenation reaction. * Free radicals become the inducers of further oxidation and can also replace intermediates through hydroxyl groups. This hydroxyl reaction replaces -SO3H, -NO2 and other groups on aromatic hydrocarbons to form unstable hydroxyl-substituted intermediates. This hydroxyl-substituted intermediate is prone to ring-opening and cleavage until it is completely decomposed into inorganic substances. In addition, chlorine dioxide can also oxidize reducing substances such as S2-. The decomposition products of chlorine dioxide can substitute certain groups in pigments. Therefore, chlorine dioxide can well oxidize and decompose refractory organic substances such as phenols, chlorophenols, mercaptans, secondary amines, and tertiary amines, as well as inorganic substances such as cyanide, sulfide, iron, and manganese in the water. In the presence of catalysts and compressed air, the decomposition of these refractory substances is accelerated, and the consumption of chlorine dioxide is also reduced. 3. Control of process conditions Catalytic oxidation is mainly used to treat refractory wastewater with high pollutant concentration. Taking coking wastewater as an example, traditional physical and chemical processes are generally used as pretreatment to reduce COD and increase PH value, making the wastewater more suitable for catalytic oxidation and reducing treatment costs. After catalytic oxidation, COD is significantly reduced and BOD5/COD is significantly increased. Biochemistry can be used to further remove COD, so that the dewatered water can meet the discharge standards. Therefore, the general process flow of catalytic oxidation treatment of coking wastewater can be determined as shown in Figure 2: Steamed ammonia removal, air flotation, catalytic oxidation, biochemical water effluent Figure 2 General process of catalytic oxidation treatment of coking wastewater The catalytic oxidation device generally adopts the form of a contact oxidation reactor, and a fixed-bed reaction tower is used based on the performance of the catalyst. Make the gas, liquid and solid phases fully contact and oxidize during the mass transfer process [7]. The main influencing factors in the catalytic oxidation reaction are: The PH value, reaction time, and oxidant dosage should be determined through experiments based on the actual situation of the coke wastewater. Change the PH value of the wastewater to promote the catalytic oxidation effect. This is mainly because chlorine dioxide shows different oxidation capabilities at different pH values. According to our wastewater tests on Wuhan Iron and Steel Coking, Jiuquan Coking, Zhenjiang Coking and other plants, the treatment effect is better under acidic to neutral conditions, which is also consistent with the strong oxidizing properties of chlorine dioxide in the pH value range. ； As the reaction time increases, the treatment effect will also increase, but after it increases to a certain value, the treatment effect will tend to be stable, and the optimal hydraulic retention time can be determined from this ； As the dosage of oxidant increases, the treatment effect also improves. When the dosage of oxidant doubles, the cost of chemicals also doubles, but the treatment effect does not double. Therefore, in order to determine the optimal value between treatment effect and operating cost, whether it is pH value, reaction time, and the amount of oxidant, it is ultimately determined based on the actual situation of the wastewater [8]. 4. Project Example The catalytic oxidation wastewater treatment device of the gas production plant of Qinhuangdao Gas Company built in 2002. The raw wastewater COD is 7446mg/L, Q = 40t/d, phenol = 150mg/L, sulfide 10mg/L. The effluent quality after catalytic oxidation treatment is detailed in Table 1 as follows (monthly data is the average of multiple tests): Project date COD (mg/L) Phenol (mg/L) Inlet and effluent removal rate Inlet and effluent removal rate 2002•6 3127.9 68.81 97.8% 540.6 1.273 99.7% 2002•9 3581.1 57.57 98.3% 617.9 4.69 99.2% 2002·12 3237.5 21.43 99.3% 493.4 0.78 99.8% 2003·2 2791.6 50.7 98.1% 480.5 1.3 99.7% 2003·5 2896.7 58.3 97.9% 318.6 5.81 98.4% 2003•8 2737 80 97% 348 2.84 99.1% 2003•10 2644.6 37 98% 274.1 4.7 98% The basic process flow is shown in Figure 3. Raw water coagulation precipitation catalytic oxidation water output Figure 3 After nearly ten years of development, the three-phase catalytic oxidation technology of wastewater treatment process in the gas plant of Qinhuangdao Gas Company has been successfully used to treat pesticide wastewater, pharmaceutical wastewater, dye wastewater, coking wastewater and chemical intermediate wastewater. There are many industrialized treatment facilities. 4. Advantages of three-phase catalytic oxidation technology 1. The catalytic oxidation reaction is carried out at normal temperature and pressure, with mild reaction conditions, high degree of automation, easy operation and low equipment investment. 2. The use of catalysts improves the oxidation efficiency and overcomes the selectivity of organic matter oxidation. The COD removal rate of coking wastewater is more than 90%, especially for the removal of refractory organic matter arsine, naphthalene, furan, pyridine, carbazole, biphenyl, terphenyl, etc., and does not produce secondary pollutants of organic halogenated hydrocarbons. It greatly reduces COD while improving biodegradability, creating conditions for subsequent biochemical treatment. ； Judging from the nature of coking wastewater, the wastewater has high concentration, complex composition, and contains a variety of pollutants that are difficult to treat with conventional processes. Therefore, it is very suitable to be treated by the three-phase catalytic oxidation method. 3. The catalyst preparation method is reliable, has long service life and low loss rate. ； The oxidant is prepared on-site using chemical methods, which is simple, has low investment and operating costs, and the raw materials are easily available ； 4. Since the COD of the effluent treated by catalytic oxidation is greatly reduced and has good biodegradability, there is no need to build a large biochemical tank, and the debugging cycle can also be * * shorten. 5. Three-phase catalytic oxidation can effectively treat coking wastewater. After biochemical treatment, the effluent can fully meet discharge standards and reduce pollutants to very low levels, which has good environmental effects. It can be seen from the above that the three-phase catalytic oxidation method, as a new catalytic oxidation technology, is an efficient treatment technology for coking wastewater and must have broad application prospects. References [1] Li Rongbo China Mercury [2] Yin Chenglong et al. Problems and solutions in coking wastewater treatment. Water Supply and Drainage, 2000, 26(6). [3] Zhang Xiaojian et al. Environmental protection for the removal of organic matter in aerobic biological treatment of coking wastewater, 1994 (8). [4] He Miao et al. Removal characteristics of organic matter in coking wastewater in activated sludge method Water Supply and Drainage, 1996, 22 (10) [5] Fang Zhenwei et al. Analysis of catalytic wet oxidation treatment of coking wastewater Industrial Water Treatment 2003, 1 [6] Huang Junli New water treatment agent - chlorine dioxide technology and its application Chemical Industry Press 2005, 5 [7], [8] He Qihuan et al. Research progress on chlorine dioxide catalytic oxidation technology for the treatment of refractory wastewater Department of Environmental Science and Engineering, Nanjing University of Science and Technology

1 Introduction Coking wastewater is produced in the coking and gas production processes. The wastewater discharge volume is large and the water quality is complex. In addition to inorganic pollutants such as ammonia, cyanide, and thiocyanate, it also contains heterocyclic and polycyclic aromatic compounds (PAHs) such as phenols, oils, naphthalene, pyridine, quinoline, and anthracene. Polycyclic aromatic hydrocarbons are not only difficult to biodegrade, but are also often carcinogens. Therefore, the large-scale discharge of coking wastewater not only causes serious pollution to the environment, but also directly threatens human health. Most of the early coking plants used the traditional activated sludge method to treat coking wastewater. However, after entering the 1990s, as people's awareness of environmental protection increased, our country gradually increased the intensity of pollution control and formulated more stringent emission standards. The "Comprehensive Wastewater Discharge Standard" (GB8978-1996) promulgated in 1996 not only added the NH3-N indicator (NH3-N＜15mg/L), but also made the CODcr emission standard more stringent (CODcr＜150mg/L). The coking wastewater treated by the traditional activated sludge method, especially the two indicators of CODcr and NH3-N, has been difficult to meet the requirements of the emission standards. According to a 1997 survey by the Ministry of Metallurgy, more than 90% of the CODcr and NH3-N processed by coking plants failed to meet standards. In order to improve the removal rate of CODcr and NH3-N, a lot of research and development work has been carried out in recent years from the aspects of microorganisms, process flows and reactors. These works mainly focus on the research of biochemical treatment technology and chemical treatment technology. 2. Progress in Bioaugmentation Technology Bioaugmentation technology is a method of adding dominant strains of bacteria selected from nature or efficient strains produced through gene combination technology to the system in order to improve the processing capacity of the wastewater treatment system to remove a certain type or type of harmful substances. The interaction between the input bacteria and the substrate mainly includes direct interaction and co-metabolism. Bioaugmentation technology emerged in the mid-1970s. Because it can improve the scope and capacity of water treatment without expanding existing water treatment facilities, its application in modern wastewater treatment has attracted increasing attention in recent years. In view of the current status of coking wastewater treatment in my country, combining bioaugmentation technology with ordinary biochemical process technology is undoubtedly a more practical idea. Naphthalene and pyridine are typical refractory organic compounds with high content in coking wastewater. Wang Jing and others isolated two strains of naphthalene-degrading bacteria WN1 and WN2 and a strain of pyridine-degrading bacteria WB1 from the activated sludge used to treat coking wastewater through domestication and enrichment culture. The enhanced effect of adding high-efficiency bacteria and microbial co-metabolism on the biological treatment of coking wastewater was studied. The results show that adding co-metabolic primary substrate, Fe3+ and high-efficiency bacteria can promote the degradation of refractory organic matter and improve the COD removal rate of coking wastewater. When the three work synergistically, the effect is better. 3. Progress in Biological Fluidized Bed Technology In recent years, biological fluidized bed has shown good development prospects in the treatment of phenolic wastewater. The biological fluidized bed uses granular materials such as sand, coke, and activated carbon as carriers. The water flows from bottom to upward, making the carrier in a fluidized state, and biofilm grows and adheres to the surface of the carrier. The carrier particle size is generally 1.0-2.0mm. The biological fluidized bed combines the dual advantages of high efficiency formed by the contact of the completely mixed activated sludge method and the ability of the biofilm method to withstand the impact of load changes. It has good treatment effects. Therefore, in recent years, it has attracted more and more attention in the treatment of refractory organic wastewater. There are four main processes in biological fluidized bed technology, namely air fluidized bed process, pure oxygen fluidized bed process, three-phase fluidized bed process and anaerobic-facultative fluidized bed process. The three-phase fluidized bed reactor is a new biochemical treatment device that organically combines biotechnology, chemical technology and water treatment technology. For example, internal circulation biological fluidized bed, air lifting circulating fluidized bed, activated carbon anaerobic fluidized bed, etc. are used to treat phenol-containing wastewater, and all have achieved relatively good phenol removal effects. In their study on the treatment of coking wastewater in a three-phase gas lift circulating fluidized bed, Cai Jian'an and others used undiluted coking sewage raw water, used NaH2PO4 as the external phosphorus source, and changed the A1LR (the treatment load of the internal circulation side settling three-phase gas lift fluidized bed reactor) by controlling the feed flow rate. When the COD inlet water load increases from 2.75kg/(d·m3) to 13.04 kg/(d.m3), the effluent phenol concentration is 0.43-1.57mg/L, and the removal rate is 99.5-99.8%. It can also maintain good relative stability under the impact of high concentrations of phenol, cyanide and COD, and the aeration amount is about 1/4-1/3 of activated sludge. Geng Yanlou uses anaerobic-anoxic-aerobic process flow, uses biofilm as anaerobic and anoxic reactor, and internal circulation biological fluidized bed as an aerobic reactor to conduct pilot application research on coking wastewater. The results show that the above process is feasible for coking wastewater treatment. When the system inlet water CODcr concentration is less than 1000 mg/L and the system hydraulic retention time is 44 hours, the outlet water CODcr concentration is less than 250 mg/L. Paul M. Sutton et al. used a fluidized bed reactor (FBR) to study the application treatment of coking wastewater from Algome Steel Plant in Canada. The wastewater flow rate was 40m3/h, the phenol content was 1000mg/L, and an equal amount of dilution water was added to control the water temperature. After two weeks, the removal rate of phenol in the fluidized bed reactor effluent reached 99% ； After 5 weeks, the thiocyanate content dropped below 5 mg/L. 4. Progress in immobilized microorganism technology. Immobilized microorganism technology is a technology that has developed rapidly in the world since the late 1960s. It is a method of immobilizing free microorganisms on a carrier through chemical or physical means to make them highly dense and maintain their activity for repeated use. It was initially mainly used for industrial microbial fermentation production and began to be used in wastewater treatment in the late 1970s. There is currently no unified classification standard for immobilized microbial technology in China, and there are many methods, including combined immobilization, cross-linking immobilization, encapsulation immobilization and self-immobilization. Wu Libo et al. used porous ceramsite adsorption and self-immobilization mixed nitrifying bacteria to treat coking wastewater, and compared the changes in bacterial activity before and after self-immobilization. The results showed that the nitrification activities of attached phase and suspended phase strains were similar, but when external conditions changed or toxic substances were present, the resistance of attached phase microorganisms was significantly stronger than that of the suspended phase. In their research on the treatment of phenol-containing wastewater using immobilized cell technology, Zhu Zhu and others proved that red brick is an excellent carrier material through experimental comparison of the degradation of phenol-containing wastewater by the same bacterial species in the fixed state and the free state, and conducted a kinetic analysis of the process of phenol degradation by cells in the two states. The results showed that in both cases, the process of phenol degradation by this strain conformed to the Monad model. Quan Xiangchun et al., in their study on the degradation of quinoline by immobilized Burkholderia picketii, screened out a strain of bacteria using quinoline as the sole carbon and nitrogen source from coked sludge through enrichment culture, and identified it as Burkholderia picketii. Immobilized gel beads and gauze-PVA (polyvinyl alcohol) composite carrier were used to immobilize, and the quinoline degradation effects of the two methods were compared. The kinetics of quinoline degradation of microorganisms immobilized on gauze-PVA composite carrier were also studied. When the quinoline concentration was 50, 100, 300, and 500 mg/L, the degradation kinetic equation followed a zero-order reaction, and the degradation rate constant increased with the increase in the initial concentration of quinoline. Sun Yan et al. isolated and purified a phenol-degrading bacterium from phenol-containing wastewater discharged from a Beijing coking plant. After acclimatization, the bacteria were embedded in sodium alginate. The processing results show that compared with free cells, the maximum reaction rates are 8.3mg.L-1.h-1 and 83.3mg.L-1.h-1 respectively, and the substrate saturation constants are 200mg/L and 285.7mg/L respectively. It can be seen that immobilized cells have great potential in degrading toxic substances. Huang Xia et al. used a composite carrier of stable, porous structure polypropylene non-woven fabric and PVA to embed and immobilize dominant bacterial species to degrade coking wastewater containing quinoline, isoquinoline and pyridine. As a result, the degradation rate of the three refractory organic matter was above 80% after 8 hours of treatment. In the study of ammonia nitrogen removal by immobilized nitrifying bacteria, Wang Lei and others used polyvinyl alcohol as an embedding carrier, added an appropriate amount of powdered activated carbon, embedded fixed nitrification sludge, and treated synthetic wastewater mainly composed of (NH4)2SO4 and glucose. Intermittent experimental results show that under the conditions of 24-28°C, particle filling rate of 7.5%, and residence time of 8 hours, the NH3-N load of the incoming water increases from 0.6kg/(d·m3) to 3.49kg/(d·m3), the NH3-N removal rate can reach 95.5%, and the COD removal rate remains above 80%. With the goal of developing immobilized microbial biological denitrification technology, Zhang Tong et al. conducted experimental studies on individual immobilization and mixed immobilization of nitrification sludge and denitrification sludge. The results show that immobilized nitrification and denitrification mixed sludge can achieve single-stage biological denitrification, and the effect is better than unimmobilized sludge. The ammonia oxidation rate and the denitrification rate of total inorganic nitrogen can be increased to 1.7 times and 13.4 times of unimmobilized sludge respectively. The results also show that light-hardening resin is also a better immobilization medium. 5 Biological denitrification technology Biological denitrification technology was developed based on ordinary biochemical treatment technology. It was first pioneered in Canada in the 1970s and first put into practical application in the United Kingdom in the 1980s. Subsequently, coking plants in France, Germany, Australia and other countries successively used this technology for sewage denitrification treatment. In my country, laboratory research on A/O (anaerobic/aerobic) treatment engineering began in the late 1980s. At present, research on biological denitrification of coking wastewater mainly focuses on AA/O (anaerobic + anoxic/aerobic) and SBR (sequencing batch batch reactor) processes. Compared with ordinary biochemical treatment processes, it can not only remove ammonia nitrogen pollutants in wastewater, but also greatly improve CODcr and other indicators. 5.1 AA/O process The AA/O process is an anaerobic-anoxic-aerobic combined process. It consists of three stages of biological treatment devices. According to the different forms of microorganisms, the AA/O process also includes activated sludge method and biofilm method. Min Zhang et al. studied the anaerobic-anoxic-aerobic (A-A/O) fixed-bed biofilm system for treating coking wastewater. The test results show that the system can remove NH3-N and CODcr stably and effectively. When the total hydraulic retention time (HRT) of the system is 31.6h, the concentrations of NH3-N and CODcr in the effluent are 3.1mg/L and 114mg/L respectively, and the removal rates are 98.8% and 92.4% respectively. Intermittent test results show that anaerobic treatment is different from anoxic treatment. Compared with anoxic treatment, the removal rate of phenol in anaerobic treatment is lower, while the removal rate of complex macromolecular organic matter is higher, and its biodegradation capacity is higher than that of anoxic treatment. In order to overcome the shortcomings of easy loss of suspended sludge, poor water quality and water quantity impact load resistance, and unstable operation, Wu Libo and others used anaerobic-anoxic-aerobic process flow (AA/O) with coking wastewater as the research object, and put spherical fillers in the aerobic section to form a composite reactor to treat coking wastewater. The test results show that the concentration of attached phase sludge in the aerobic composite reactor is higher than that of suspended phase sludge. The attached phase sludge has a higher degradation ability and anti-inhibition ability for three representative pollutants in coking wastewater: phenol, quinoline and ammonia nitrogen than suspended phase sludge. Li Yongmei used anaerobic acidification-anoxic-aerobic (AA/O) biofilm method to treat Shanghai coking plant wastewater. The test results show that when the incoming water COD is 600-1000mg/L and the ammonia nitrogen is 200-280mg/L, in order to achieve good organic matter removal and denitrification effects at the same time, the HRT of the system should be at least 34.5h, the mixed liquid reflux ratio should be 4.0-5.0, the pH value of the aerobic section should be maintained at 7.8-8.0, and the residual alkalinity of the effluent should be 100-200mg/L. Methanol needs to be added as an external carbon source in the anoxic section. The ratio of methanol to nitrate nitrogen is 2.58.: 1 is appropriate. 5.2 SBR process SBR is a new activated sludge process developed in recent years. In the same reactor, it sequentially completes the anoxic, anaerobic and aerobic processes through programmed control of the five stages of water filling, aeration reaction, sedimentation, drainage, and sludge discharge to achieve biochemical treatment of wastewater. Practice has proven that when the SBR process is used to treat high-concentration and refractory organic matter and biologically remove nitrogen, phosphorus and sulfur, it can obtain much better effluent quality than the conventional activated sludge method. Hanqing Yu et al. used SBR process to treat coking wastewater. The results show that using anoxic treatment before and after the aeration section has a better denitrification effect than using other methods (pre-denitrification and post-denitrification). The 4-h anoxic treatment can cause some substrates in the incoming water to be stored in the organisms, leading to denitrification in the second anoxic stage. Under the above conditions, the removal rates of NH3-N and CODcr were 82.5% and 65.2% respectively. Some readily biodegradable organic matter in the feed water, such as phenols and cresols, are used as carbon sources in the denitrification stage. Aeration for 16 hours significantly reduced the concentrations of cresol, 3,4-xylenol and 2-quinoline ethanol, but the removal of quinoline, isoquinoline, indole and methylquinoline was not obvious. Min Woo Lee et al. used sodium acetate as an external carbon source to study the feasibility of using the SBR process to completely remove NH3-N from coking wastewater. The results show that the addition rate of external carbon source can significantly affect the efficiency of denitrification, and the optimal rate is determined by the ratio of COD to NOx-N in the denitrification stage. In the biological denitrification system, the total removal rate of soluble pollutants in wastewater is greater than 95%. Considering that the traditional A/O or AA/O process cannot reduce the COD of coking wastewater to less than 100 mg/L, Li Chunjie and others introduced PVDF (polyvinylidene fluoride) hollow fiber membranes into the SBR reactor, that is, an integrated membrane sequencing batch bioreactor (SMSBR) was used to enhance the treatment of coking wastewater. Preliminary research results show that under the conditions of HRT of 32.7h, mud age (SRT) of 600d, and average COD volume load of 0.45kg/(d·m3), COD in the membrane effluent can be stabilized below 100mg/L (average 86.4mg/L). The COD trapped by the membrane is further degraded in subsequent reactions without significant accumulation. ； Under the condition of ensuring temperature and alkalinity, the NH3-N concentration of the effluent should be lower than 1mg/L. In this process, the membrane fouling rate is relatively fast. 6 Progress in Chemical Technology 6.1 Catalytic Wet Oxidation Technology Catalytic wet oxidation technology uses air to oxidize ammonia nitrogen and organic pollutants in wastewater under high temperature and high pressure conditions under the action of a catalyst, and ultimately converts them into harmless substances N2 and CO2 for emission. Research on this technology began in the 1970s. Coking chemical industry, petrochemical industry, especially toxic pollutants such as: Pesticides, dyes, rubber, synthetic fibers, flammable, explosive and difficult-to-biodegrade high-concentration wastewater are all suitable for catalytic wet oxidation treatment. Our country's research in this field is also relatively early. From 1987 to 1992, Anshan Jiao Yuan cooperated with the Dalian Institute of Physics and Chemistry of the Chinese Academy of Sciences to successfully develop a two-component highly active catalyst, which has a good treatment effect on high-concentration total nitrogen and organic coking wastewater. The disadvantage of this technology is that the catalyst is expensive. In recent years, there have been few domestic and foreign research reports on the use of catalytic wet oxidation technology to treat coking wastewater. 6.2 Electrochemical oxidation technology Li-Choung chiang et al. used PbO2/Ti as electrodes to study the treatment of coking wastewater by electrochemical oxidation. The results showed that after 2 hours of electrolysis, COD in the wastewater dropped from 2143 mg/L to 226 mg/L, with a removal rate of 89.5%. In addition, approximately 760 mg/L NH3-N in the wastewater is also removed at the same time. The study found that electrode materials, oxide concentration, current density and pH value have a significant impact on the removal rate of COD and the efficiency of current during the electrochemical oxidation process. In addition, the chloride/high chloride produced during the electrolysis process can cause indirect oxidation, which plays an important role in the removal of pollutants from coking wastewater. 6.3 Use flue gas to treat coking remaining ammonia or all coking wastewater In order to completely solve the pollution problem of coking wastewater, Yin Guangjin and others adopted a treatment technology that is completely different from the biochemical method, that is, using flue gas to treat coking remaining ammonia or all coking wastewater. This technology has obtained an invention patent and has been successfully used in the coking residual ammonia water treatment project of Jiangsu Huaigang Group. In the boiler flue gas treatment process for coking residual ammonia water, the wastewater contacts the flue gas in the spray tower and undergoes physical and chemical reactions. All wastewater is vaporized, and chemical reactions occur between SO2 in the flue gas, NH3 in the wastewater, and O2 in the tower to generate (NH4)2SO4. The organic pollutants adsorbed in the smoke are decomposed non-toxically in the high-temperature roasting furnace or boiler furnace, so that the entire process achieves zero discharge of waste water and does not cause pollution to the atmospheric environment. This process "treats waste with waste", which not only has good treatment effects, but also has the advantages of low investment and low operating costs. 7 Conclusion In recent years, with the increasingly stringent emission standards, scholars from various countries have conducted some new and useful explorations in coking wastewater treatment technology. Bioaugmentation technology can improve the scope and capacity of water treatment on the basis of existing sewage treatment facilities, and is more suitable for the current status of sewage treatment in my country's coking industry ； Immobilized microbial technology, biological denitrification technology and biological fluidized bed technology have improved traditional biochemical treatment technology from all aspects of microorganisms, process flow and reactors, and will have good application prospects in coking wastewater treatment. ； Chemical technology provides a new idea for the treatment of coking wastewater. Compared with biochemical technology, this method has simple process, fast reaction speed and high purification rate. However, the disadvantage is that the investment and treatment costs are high. summary: Coking wastewater is a refractory organic wastewater with high ammonia nitrogen and organic matter concentrations. This article systematically introduces the research progress in coking wastewater treatment at home and abroad in recent years. Bioaugmentation technology can improve the treatment scope and processing capacity based on the original facilities, and is more suitable for the current situation of coking wastewater treatment in my country ； Immobilized microbial technology, biological denitrification technology and biological fluidized bed technology have effectively improved traditional biochemical treatment technology and will have good application prospects in coking wastewater treatment. ； Compared with biochemical technology, chemical technology has simple processes, fast reaction speed, and high purification rate, but its disadvantage is that investment and treatment costs are higher.

Summary: Taking a coking plant with a coke production capacity of 600,000 t/a as an example, using the process parameters given in actual design or experiments for calculation, it was concluded that the operating costs of using three technologies: ordinary biochemistry, A/O biological denitrification and catalytic wet oxidation to treat the same coking source wastewater - residual ammonia water, are 25.35 yuan/m3, 28.77 yuan/m3 and 29.72 yuan/m3. There is no significant difference between the three, and they can be accepted by coking enterprises. Keywords: Common biochemical method A/O biological denitrification catalytic wet oxidation operating cost comparison 0 Introduction? Catalytic wet oxidation treatment technology and A/O biological denitrification sewage treatment technology are coking wastewater treatment technologies developed in the early 1990s. Both can better oxidatively degrade COD components and ammonia nitrogen pollutants in coking wastewater, so that various pollution indicators in the wastewater can be discharged up to standards. Catalytic wet oxidation treatment technology can also effectively treat BaP and other condensed aromatic hydrocarbon compounds that are difficult to biodegrade, and can decolorize, deodorize, and sterilize. The treated effluent can meet the reuse requirements (effluent quality is shown in Table 1). Compared with ordinary biochemical methods, for a coking plant with an annual output of 450,000 tons of coke, both technologies can reduce the emission of pollutants ammonia nitrogen and CODCr by about 100 tons per year, which has significant environmental benefits. 　?Table 1 Effluent water quality treatment process of three treatment technologies Effluent water quality process name CODCr (mg/L) NH3-N (mg/L) BaP (μg/L) Ordinary biochemical method 200 180 25 A/O biological denitrification method 100 10 20 Catalytic wet oxidation method <50 <10 <2 However, nearly 10 years have passed, and these two excellent water treatment technologies have not played their due role in actual production applications. Among them, A/O biological denitrification treatment technology is only used by a few companies such as Baosteel Coking Plant. Catalytic wet oxidation treatment technology has not yet been adopted by any coking plant (or gas plant). This is extremely disproportionate to the current situation in my country where the water environment is seriously affected by ammonia nitrogen pollution. The main reason is that catalytic wet oxidation treatment technology oxidizes harmful pollutants in wastewater under high temperature and high pressure conditions, and its catalyst is a precious metal compound. ； The equipment and facilities of the A/O biological denitrification treatment process are relatively larger than those of ordinary biochemical treatment processes of the same scale. The process also uses expensive sodium bicarbonate or other alkali sources during its operation. Therefore, compared with ordinary biochemical methods, the unit operating costs of both are much higher. Just like this, people have reason to think that: Although the two coking wastewater treatment technologies have good sewage treatment effects, their expensive operating costs are unaffordable for many companies. Due to technical differences among the three wastewater treatment methods, the requirements for incoming water quality are different. ； As a result, for the same coking plant source wastewater, the required pretreatment conditions are also different, and the scale of wastewater treatment facilities is also different. Under such a premise, it would be unscientific to draw conclusions simply by comparing the unit operating costs of the wastewater treatment facilities themselves. In order to explore the application prospects of two wastewater treatment technologies, the author here conducts a comparative study on the operating costs of catalytic wet oxidation technology and A/O biological denitrification treatment technology and the operating costs of ordinary biochemical treatment technology widely used in existing coking plants, so as to provide reference for design departments and leaders of coking plants, gas plants and other enterprises when making decisions on coking wastewater treatment plans. 1 Prerequisite for cost calculation and comparison? Coking wastewater is wastewater formed during the high-temperature carbonization of coal, gas purification, and chemical product refining. This is an industrial wastewater with complex composition, high concentration, high toxicity, and refractory degradation. It is mainly formed by remaining ammonia (gas condensate). When the ordinary biochemical treatment process and the A/O biological denitrification treatment process are used, since the COD components and ammonia nitrogen concentration in the wastewater are both high, in order to ensure the normal operation of the treatment process, the wastewater must first be pre-treated such as ammonia steaming ； Catalytic wet oxidation treatment technology does not require ammonia pretreatment. Therefore, when calculating and comparing operating costs, the ordinary biochemical treatment process and the A/O biological denitrification treatment process need to include this part of the cost. In addition, given that there are many coking processes, especially gas purification and chemical product recycling processes, the wastewater discharge sources and the quality of the coking wastewater produced by various processes are also different. In comparison, when the gas purification process is the production of ammonium sulfate and the desulfurization and decyanization process, the wastewater discharged is most suitable to be treated by the catalytic wet oxidation process. Therefore, in order to calculate operating costs on the same basis, for a coking plant with an annual coke output of 600,000 tons, the recovery and gas purification process is based on ammonium sulfate, and it is equipped with a desulfurization and decyanization device (such as FRC or T?H process), and the evaporated ammonia must be considered as removing fixed ammonia. At this time, the remaining ammonia water, crude benzene separated water, etc. to be treated total about 15m3/h. The process routes of the three treatment technology solutions are as follows. (1) Ordinary biochemical coagulation treatment process (see Figure 1): Remaining ammonia → steamed ammonia stripping → biochemical treatment → coagulation treatment → discharge ↑ ↑ ↑ ↑ ↑ NaOH steam dilution water NaOH coagulant? Figure 1 Ordinary biochemical treatment (2) A/O biological denitrification? Coagulation treatment process (see Figure 2): Residual ammonia → steamed ammonia stripping → A/O biological denitrification → coagulation treatment → discharge ↑ ↑ ↑ ↑ ↑ ↑ NaOH steam Na2CO3 a small amount of dilution water NaOH coagulant? Figure 2 A/O biological denitrification treatment (3) catalytic wet oxidation treatment (see Figure 3): Remaining ammonia → catalytic wet oxidation treatment → discharge ↑ NaOH? Figure 3 Catalytic wet oxidation treatment? The water volume treated is 60m3/h, 50m3/h, and 15m3/h based on the water volume entering the biochemical treatment device, A/O biological denitrification device, and catalytic reaction device, respectively. The treatment process conditions are: The process parameters of steamed ammonia, ordinary biochemical treatment, and A/O biological denitrification are selected according to the current general parameters, and the process parameters of catalytic wet oxidation are calculated according to the parameters listed in the small test results. Based on this calculation, the technical and economic indicators of the three treatment processes are shown in Table 2 (the treated water volume is calculated as 15m3/h). ?2 Comparative calculation of operating expenses? 2.1 Calculation conditions of operating expenses? The various prices calculated here are as follows. (1)Raw material prices: 　Sodium hydroxide (30%): 400 yuan/t, Na2CO3: ?1200?yuan/t Polyferric sulfate: 350 yuan/t, phosphoric acid (85%): ?2150? Yuan/t ?Table 2 Technical and economic indicators Project unit Ordinary biochemical A/O Biological denitrification catalytic wet oxidation NaOH (30%) t/a 940 935 876 Na2CO3 t/a 490 Polymeric ferric sulfate (PFS) t/a 160 135 Phosphoric acid (85%) t/a 30 25 Industrial water m3/a 210000 140000 Electricity consumption kW·h/a 630000 450000 3540200 Steam t/a 28380 27830 Gas volume m3/a 1251500 Circulating water m3/h 100 100 45 Other infrastructure investment of 10,000 yuan 700 750 773 Capacity: 22 22 10 (2) Power price: 　?Industrial water: 1.0 yuan/m3, electricity: 0.4 yuan/(kW·h), steam: 45 yuan/t, gas: 0.9 yuan/m3, circulating water: 0.15 yuan/m3? (3) Workers’ wages and surcharges: 12,000 yuan/(person·year). ?(4) Catalyst replacement cost: 　After the catalyst has been running for 5 years, all catalysts must be replaced, and the cost of one replacement is 400,000 yuan/m3. ?(5) Workshop expenses: Including depreciation, major, medium and minor repairs and others. For catalytic wet oxidation technology, since the catalyst is replaced every five years and has been depreciated, this part of the cost should be deducted from the depreciation. The operation of the device is based on 20 years, and the depreciation rate is 5% per year (infrastructure investment deducts recovery costs). Major, medium and minor repairs and other expenses are valued at 5% of the equipment investment cost. Other wastewater treatment methods, depreciation and major, medium and minor repairs and other expenses are valued at 5% of their infrastructure investment. ?(6) When calculating fees, land use fees, sewage discharge fees required for discharging wastewater and penalty fees for excessive discharge of pollutants are not taken into account. 2.2 Calculation results Based on the above calculation conditions, the calculation results shown in Table 3 are obtained. It can be seen from this point that the unit operating costs of ordinary biochemical method, A/O biological denitrification technology and catalytic wet oxidation technology, starting from the source of wastewater, are respectively: 25.35 yuan/m3, 28.77 yuan/m3, 29.72 yuan/m3 ； The ratio of the three is 1:1.135:1.172. Compared with the former, although the unit operating costs of A/O biological denitrification technology and catalytic wet oxidation technology are higher, there is no significant difference between them, and they can be accepted by enterprises such as coking plants (gas plants) in my country. Considering only the wastewater treatment device, excluding the cost of pre-treatment facilities such as ammonia evaporation, and calculating based on the scale of the wastewater treatment facility, the operating cost of the ordinary biochemical method is no more than 5 yuan/m3, and the operating cost of the A/O biological denitrification technology is 8 yuan/m3, nearly twice the former. ； The operating cost of catalytic wet oxidation treatment technology is still 29.72 yuan/m3, which is 5 to 6 times that of ordinary biochemical methods. This cost comparison is obviously unfair. 　?Table 3 Operating cost results of three treatment technologies Project unit Ordinary biochemical A/O Biological denitrification catalytic wet oxidation NaOH (30%) Yuan 376000 374000 350400 Na2CO3 Yuan 588000 Polyferric sulfate (PFS) Yuan 56000 47250 Phosphoric acid (85%) Yuan 64500 53750 Industrial water yuan 210000 140000 Electricity consumption yuan 252000 180000 1416080 Steam yuan 1277100 1252350 Gas yuan 1126350 Circulating water yuan 131400 131400 59130 Workers' wages and surcharges yuan 264000 264000 120000 Catalyst replacement cost RMB 600000 Depreciation RMB 350000 375000 116500 Major, medium and minor repairs and other RMB 350000 375000 116500 Total RMB 3331000 3780750 3904960 Unit operating cost RMB/m3 25.35 28.77 29.72 3 Conclusions and Suggestions It can be seen from the above calculation results that the operating costs of catalytic wet oxidation treatment technology and A/O biological denitrification treatment technology are not significantly different from ordinary biochemical methods, and the maximum difference between the three does not exceed 20%. If we also consider land use fees, sewage fees and excessive penalty fees, to a certain extent, the treatment costs of ordinary biochemicals may be higher than those of A/O biological denitrification technology and catalytic wet oxidation technology. Therefore, from the perspective of controlling pollution and protecting the environment, the author suggests that corporate decision-makers and design departments should try their best to promote the implementation of A/O biological denitrification treatment technology and develop catalytic wet oxidation treatment technology, and put the transformation of ordinary biochemical treatment projects in existing coking plants (gas plants) on the agenda as soon as possible

summary: The article focuses on the physical and chemical methods used in the treatment of coking wastewater, as well as the research and application of these technologies and methods. keywords: Coagulation and adsorption wastewater treatment of coking wastewater 1 Introduction Coking wastewater is high-concentration organic wastewater produced in the process of coal-to-coke production, gas purification and coking product recovery. Its composition is complex and contains a large amount of organic pollutants such as phenols, biphenyl, pyridine, indole and quinoline. It also contains toxic and harmful substances such as cyanide, inorganic fluoride ions and ammonia nitrogen. The pollutants have high color and are high-concentration organic industrial wastewater that is difficult to biochemically degrade.');">Industrial wastewater. Therefore, the treatment of coking wastewater has always been a major problem in the field of wastewater treatment at home and abroad. 　　At present, the technologies for treating coking wastewater mainly fall into three categories: physicochemical method, biochemical method and physicochemical-biochemical method. Among them, the physicochemical method is simple and easy to implement and has been widely used in the treatment of coking wastewater. 2 Physicochemical treatment technology of coking wastewater 2.1 Adsorption method The adsorption method for treating wastewater is to use porous adsorbents to adsorb one or several solutes in the wastewater to purify the wastewater. Commonly used adsorbents include activated carbon, sulfonated coal, slag, diatomite, etc. This method has high treatment costs, difficult adsorbent regeneration, and is not conducive to treating high-concentration wastewater. 　　Xia Haiping and Ke Jiajun studied the adsorption effect of bentonite clay mineral on ammonia nitrogen in coking wastewater. The study showed that natural bentonite can effectively adsorb ammonia nitrogen in coking wastewater. ； The adsorption effect of granular bentonite is better than that of powdered bentonite. 　　Wu Shengbiao, Xiao Bo, Shi Xiaoyan and others studied and compared the COD removal efficiency of powdered activated carbon and columnar activated carbon in coking wastewater. The results showed that the COD removal rate of powdered activated carbon can be as high as 98.5%. ； At the same time, the particles of powdered activated carbon have an optimal size range, and powdered activated carbon with a particle size of 0.09mm has the highest COD removal rate from coking wastewater. 　　Fly ash treatment wastewater has been one of the hot topics in the comprehensive utilization of fly ash in recent years. The main components of fly ash are silica and silicates. When fly ash is used as an adsorbent to deeply treat coking wastewater, it has good decolorization effect, good removal effect of COD, volatile phenol, oil, etc., and low cost. 　　Liu Xinxin, Yao De, Dong Fengzhi, and Yang Xinchun gained a preliminary understanding of the mechanism of fly ash treatment of wastewater. Its function is basically adsorption, including physical adsorption and chemical adsorption. The adsorption law conforms to the Freundlich adsorption isotherm. 　　Zhang Changming, Li Aiying, etc. conducted research on the purification and treatment of coking biochemical effluent using fly ash as an adsorbent under laboratory conditions. They pointed out that when the amount of fly ash added is 1.5g/100mL and the soaking time is 20 to 25 minutes, all indicators of the treated wastewater, except ammonia nitrogen, can meet the efflux standards. 2. 2 Chemical precipitation method Liu Xiaolan, Wang Jihui, Huang Wenshui, etc. used chemical precipitants MgCl2·6H2O and Na2HPO4·12H2O (or MgHPO4·3H2O) to pretreat the remaining ammonia water from coking, and achieved good results. The removal rate of ammonia nitrogen in wastewater was as high as more than 99%. The precipitant reacts with NH4+ in the coking wastewater to form magnesium ammonium phosphate precipitate. Under the condition of pH 8.5-9.5, when the added agent Mg2+: NH4+: PO43- (molar ratio) is 1 4: 1: 0.8, the removal rate of ammonia nitrogen in the wastewater reaches more than 99%, and the mass concentration of ammonia nitrogen in the effluent drops from 2000 mg/L to 15 mg/L. achieve * * emission standards. 2. 3 Coagulation and precipitation method The coagulation method is to add coagulant to wastewater and hydrolyze it to produce hydrated ions and hydroxide colloids, which neutralize the charges on the surfaces of certain substances in the wastewater, causing these charged substances to agglomerate. The key to the coagulation method lies in the coagulant. At present, domestic coking manufacturers generally use polyferric sulfate (PFS), and the coagulant is polyacrylamide (PDM). Zhao Ling and Wu Mei studied the application of coagulation and clarification method in the treatment of coking wastewater. Production practice has proved that the coagulation and clarification method is used to deeply treat coking and biochemical wastewater. The dosage of polyferric sulfate (PFS) is 20~30 mg/L and the dosage of polyacrylamide is 0.25-0.13 mg/L. It can remove 45% of COD and 37% of cyanide, achieving good results. 　　Shanghai Coking Plant uses anaerobic-aerobic biological denitrification combined with poly-iron flocculation mechanical accelerated clarification method to comprehensively treat coking wastewater, reducing COD in the effluent

In recent years, my country's coking industry has made great progress, and its technical equipment and environmental protection management levels have been significantly improved. In 2005, my country's coke output reached 243 million tons, an increase of approximately 17.9% over the previous year. While my country has become a major producer and exporter of coke in the world, it has also left pollution within the country. The coking industry is one of the main industries causing environmental pollution in my country. Adhering to the harmonious unity of economic, social and environmental benefits, increasing the treatment of coking wastewater, and promoting the pace of cleaner production have become one of the extremely urgent tasks currently faced by my country's coking industry. The particularity of coking wastewater treatment: Coking wastewater is produced in the process of coking and chemical product recovery and refining. Its treatment difficulties include the following aspects:: The first difficulty is the large amount of wastewater discharge and the complex water quality composition. It contains more than 50 kinds of inorganic and organic compounds, including ammonia nitrogen, cyanide, benzopyrene, monocyclic, polycyclic and even heterocyclic aromatic compounds. Phenols and their derivatives account for about 60%, and they are difficult to biodegrade. ； The second difficulty is the high concentration of ammonia nitrogen. In the case of steamed ammonia wastewater, the COD content is generally as high as 4000 mg/L, and the total ammonia nitrogen content is around 500 mg/L, which has exceeded the limit of traditional biological treatment. ； The third difficulty is that the coking wastewater produced by my country's coking process is also typically local, resulting in the inability of some advanced foreign technologies to effectively solve the problem of coking wastewater treatment in my country. Before the 1990s, most coking plants in my country only used biological dephenolization processes to treat coking wastewater. Coking plants later built or renovated used the ordinary activated sludge method. This method has a low removal rate of ammonia nitrogen and the cost of wastewater treatment is as high as 6 yuan/ton to 8 yuan/ton. The difficulty of clean production in iron and steel enterprises lies in the coking process. The focus of environmental pollution control in the coking process is sewage treatment. The main purpose of coking sewage treatment is to remove organic matter and ammonia nitrogen. Since ammonia nitrogen and polycyclic aromatic hydrocarbons in coking wastewater have toxic and inhibitory effects on microorganisms, the treatment of coking wastewater has become an international technical problem. developed * * The fundamental reason why a large number of coking companies have been closed is due to environmental pressure. At present, most coking enterprises in my country use the conventional activated sludge method for wastewater treatment, which has a small treatment capacity and little effect on nitrogen removal, and cannot meet the requirements of coking wastewater discharge standards. Therefore, it is particularly necessary to develop and research efficient and applicable coking wastewater purification technology and accelerate the pace of coking wastewater treatment. The urgency of denitrification of coking wastewater Wastewater discharge from the coking industry has caused serious pollution to the ecological environment. In recent years, * * A series of relevant regulations have been introduced for the coking industry, such as eliminating soil coking and restricting small machine coking. Some large and medium-sized coking enterprises in our country strictly implement * * The standards related to cleaner production have intensified the treatment of coking wastewater, improved resource utilization, and changed the situation of serious environmental pollution by coking wastewater. According to relevant statistics in 2003,: There are 39 companies in my country's coking industry that have reached the second level or above clean production standards of HJ/T126-2003 "Cleaner Production Standard (Coking Industry)", accounting for 9.75% of the total number of coking companies in my country. ； There are 32 enterprises that have reached Level 3 or above standards, accounting for 8.0% of the total number of coking enterprises. ； Less than 20% of coking enterprises have built sewage treatment devices with denitrification function. But at the same time, the wastewater discharged by many coking companies has exceeded the carrying capacity of the river sections in the region. While causing river pollution and ecological environment damage, it has also put great pressure on companies to survive. Considering the high cost of coking wastewater treatment, many coking companies in my country have their wastewater purification devices switched on and off. Those small coke manufacturers with an annual output of less than 500,000 tons do not have coking wastewater treatment facilities installed, which further exacerbates the deterioration of the ecological environment. In recent years, the recovery of the world economy and the rapid development of the steel industry have promoted the rapid development of my country's coking industry. However, the treatment methods for coking wastewater in my country's coking industry are limited to ordinary biological removal of phenolization technology, and COD and ammonia nitrogen are not treated. “During the Tenth Five-Year Plan period, my country's coke production increased annually by 14.82%. In 2005, 61 new coke ovens were built and put into operation, adding about 27 million tons of new coke production capacity. my country's coking enterprises have improved their equipment level by adopting a large number of new technologies, but some wastewater treatment facilities for expansion and reconstruction of coke ovens still cannot be matched simultaneously. This causes the total amount of coking wastewater pollution to increase with the increase in coke production. For some old plants, due to my country's insufficient environmental protection legal system and other reasons, there is insufficient capital investment in wastewater treatment, and the "three synchronizations" cannot be achieved during coking technology transformation. From a national perspective, the total amount of pollutants discharged by my country's coking industry has increased unabated in recent years. In the next 20 years, our country will fully implement comprehensive pollution reduction policies. The "Eleventh Five-Year Plan" Environmental Protection Plan emphasizes that more stringent total pollutant emission control policies will be implemented. As one of the more polluting industries, the coking industry must adhere to the development of a circular economy, pay attention to wastewater treatment, effectively control the total amount of emissions, increase production without increasing pollution when building, expanding, and rebuilding projects, and strive to achieve "zero" wastewater discharge and reuse of water resources. Coking wastewater denitrification technology needs to be optimized urgently. Coking wastewater denitrification technology includes physical and chemical methods, biochemical methods, etc. The biochemical method is a typical process technology that is relatively economical, effective, has no pollution transfer, and is easy to operate and easy to master. Biological denitrification uses the biochemical action of microorganisms to convert ammonia nitrogen in wastewater into harmless nitrogen through nitrification and denitrification reactions and remove it. At present, the main biochemical denitrification processes used in domestic coking wastewater treatment include the "anoxic-aerobic (A-O)" method and the "anaerobic-anoxic-aerobic (A-A-O)" method developed on the basis of this process. In addition, the "anoxic-aerobic-aerobic (A-O-O)" method is also an extension of the "AO" process, and both belong to the biological denitrification process with "anoxic-aerobic" as the basic process. “The anoxic-aerobic" biochemical denitrification process is as follows: The coking wastewater undergoes nitrification reaction in the aerobic tank. After the ammonia nitrogen is directly oxidized into nitrate nitrogen, it returns to the anoxic tank for denitrification reaction, where the nitrate nitrogen is reduced to nitrogen and escapes, achieving the removal of total nitrogen and the degradation of COD. Our country began to study the "anoxic-aerobic" process in the 1980s. In 1993, this process was applied in the first and second phases of Baosteel's coking wastewater treatment projects, and was later optimized into the "A-O-O" process, which not only improved the purification effect, but also reduced operating costs. Biological denitrification technology using activated sludge has been applied in coking plants of Panzhihua Iron and Steel Co., Ltd., Kunming Iron and Steel Co., Ltd., Shougang Iron and Steel Co., Ltd., Lianyuan Iron and Steel Co., Ltd., and has achieved good denitrification effects. The treated wastewater has reached * * According to the secondary emission standard, the removal rate of ammonia nitrogen and COD can reach more than 95%. These three processes have relatively strict requirements on working conditions, high requirements on the living environment conditions of microorganisms, high investment and operation costs, and limited wastewater treatment capacity, generally below 60 tons/hour, which limits their promotion and application in large and medium-sized coking enterprises. With the expansion of large and medium-sized steel companies, coke production has also reached 3 million tons/year to 4 million tons/year, so it is particularly urgent to develop coking wastewater treatment devices with a capacity of more than 200 tons/hour. Countermeasures for denitrification of coking wastewater Coking production consumes a large amount of energy. The discharge of coking wastewater destroys the ecological environment and causes huge economic losses, which puts great pressure on the coking industry itself and society. my country's coking industry must strengthen its own technological adjustments and change its extensive economic growth model. Specifically, the countermeasures for denitrification of coking wastewater in my country include the following aspects:: First, establish and improve * * Strengthen the coking wastewater treatment mechanism that combines supervision and corporate self-adjustment. “During the Eleventh Five-Year Plan, * * We will strengthen the environmental supervision system, further establish and improve the long-term mechanism for environmental protection, and use policy guidance and legal constraints to coordinate the development of the coking industry. ； Scientifically implement the control of the total discharge of water pollutants, establish a total discharge control system with key pollution sources as the main body, and make pollution prevention and control one of the main tasks in the future. * * It is clearly stated that by 2010, 100% of the coking wastewater discharged by my country's coking industry will meet the discharge standards, and the total discharge amount will be controlled not to exceed the total discharge amount specified by the local environmental protection department. The "Coking Industry Pollutant Emission Standards" also clearly stipulates that as of January 1, 2009, the maximum allowable concentrations of COD and ammonia nitrogen in coking wastewater discharged by my country's coking enterprises are 100 mg/L and 15 mg/L respectively. However, currently more than 80% of my country's coking enterprises are still far away from this indicator. my country's coking industry requires space for survival and development. The direction and goals of corporate structural adjustment must be based on energy conservation and consumption reduction and environmental governance, and establish a development model of a conservation-minded, clean, and recycling enterprise that meets pollutant emission standards and rationally utilizes resources. The second is to research and develop efficient and cheap denitrification processes. As a typical industrial wastewater containing refractory organic matter, coking wastewater's treatment technology and technology have become a hot research topic at home and abroad. In the past 10 years, relevant scientific research institutes, universities and coking enterprises in my country have conducted useful explorations on the "aerobic-anaerobic" reaction mechanism, influencing factors, process length and other theories of biological denitrification technology based on the application of the "A-O" process, proposed some new biological denitrification concepts and theories, and developed technologies such as "intermittent sequence batch biological denitrification" and "catalytic wet oxidation". The core of biochemical treatment of coking wastewater is the use of microorganisms to decompose organic matter. Only by obtaining bacteria with strong adaptability and high decomposition ability can the advantages of biochemical treatment be exerted in a suitable process. Relevant domestic parties have successfully developed efficient microbial groups. Relevant scientific research units have also optimized the "A-O" process and developed the "anoxic-aerobic-aerobic (A-O-O)" internal cycle denitrification process. The future tasks of our country’s relevant scientific and technological workers are: Combining the actual situation of the coking industry and the difficulties of the "A-o" denitrification process of coking wastewater, through the combination of "production, learning, and research", breakthroughs were made in the core and key technologies of coking wastewater treatment, and a large denitrification device with a wastewater treatment capacity of 100 tons/hour or even more than 200 tons/hour, low infrastructure investment, high biological denitrification efficiency, and stable operation was developed. The third is to promote the application of mature and effective coking wastewater treatment technology. my country's coking enterprises should control coking wastewater from the source and process the manpower, and integrate the concept of clean production throughout the entire coking production process to improve resource utilization and reduce the use of industrial water and steam. For wastewater generated from chemical production systems, enterprises should implement "small water concentration, separation of clear and turbid water, and small-radius circulation, limit and eliminate backward processes and equipment that seriously waste resources and energy, and encourage the application of low- and non-polluting processes with high resource utilization efficiency." In the process of wastewater generation, enterprises should strengthen pollution prevention and control, and actively promote technologies such as steam-free ammonia evaporation, horizontal tube coolers, and thermal oil heat transfer for primary and final cooling of gas, so as to reduce the amount of wastewater generated from the source. Jigang Coking Plant and Laigang Coking Plant have achieved remarkable results in achieving "zero" discharge of coking wastewater.: They use coking wastewater that meets secondary emission standards after treatment as blast furnace slag and circulating water supplementary water. This is worth promoting to other companies. In addition, relevant units should also accelerate research on the "nitrification-denitrification" treatment of ammonia nitrogen microorganisms in coking sewage, and gradually move it towards large-scale, efficient and applicable ； Develop and improve intelligent control modes for new aeration equipment, micropore aerators, rotating water distributors and automatic detection technology for sewage treatment ； Apply membrane bioreactor technology to develop efficient sewage treatment agents, and encourage the application of ozone, ultraviolet and other disinfection technologies without secondary pollution in wastewater treatment. When coking enterprises in my country choose wastewater treatment processes, they must take into account local conditions and comprehensive considerations, and determine the process flow based on the actual concentration of organic matter in the wastewater, so that they can achieve the desired denitrification effect.

Coking wastewater is produced during the high-temperature carbonization of raw coal, gas purification and chemical product refining. The composition of wastewater is complex, and its water quality changes with the composition of raw coal and the coking process. Shown in NMR chromatogram: Coking wastewater contains dozens of inorganic and organic compounds. Among them, inorganic compounds mainly include large amounts of ammonia salts, thiocyanide, sulfide, cyanide, etc. In addition to phenols, organic compounds also include monocyclic and polycyclic aromatic compounds, heterocyclic compounds containing nitrogen, sulfur, and oxygen. In short, coking wastewater is seriously polluted and is a prominent environmental problem in industrial wastewater discharge. "Comprehensive Wastewater Discharge Standard" (GB8978-96) Requirements for New Renovation and Expansion Projects of Coking Wastewater: NH 3 -N≤15mg/L, COD≤100mg/L. In the past, biochemical methods were mainly used to remove NH 3 -N and COD in coking wastewater at home and abroad, among which the ordinary activated sludge method was the main method. This method can effectively remove phenol and cyanide substances in coking wastewater, but the removal effect of refractory organic matter and NH 3 -N is poor, making it difficult to meet discharge standards. The treatment of refractory organic matter has attracted great attention from relevant scholars at home and abroad. Many scholars have conducted a lot of research on refractory organic matter. At the same time, they have improved the NH 3 -N removal process in coking wastewater and proposed many practical treatment facilities and technologies to reduce the concentration of effluent COD and NH 3 -N. * * reduce. This article will introduce several advanced and effective coking wastewater treatment technologies. 1 Pretreatment technology of coking wastewater Biological treatment is mainly used to remove organic matter in coking wastewater, but some of the organic matter is not easy to biodegrade, so appropriate pretreatment technology is required. The commonly used pretreatment method is anaerobic acidification. Anaerobic acidification is a process between anaerobic and aerobic. Its mechanism is to change the chemical structure of refractory organic matter through hydrolysis and acidification of anaerobic microorganisms to generate easily degradable substances. Anaerobic microorganisms have different metabolic processes from aerobic microorganisms in the cleavage of rings in heterocyclic compounds and polycyclic aromatic hydrocarbons, and their cleavage is reductive cleavage and non-reductive cleavage. Anaerobic microorganisms have a sound ring-opening enzyme system that is easily induced and relatively diverse, making it easy for heterocyclic compounds and polycyclic aromatic hydrocarbons to undergo ring-opening and cleavage. There are a lot of easily degradable organic matter in coking wastewater, which can be used as the primary energy and carbon source for microbial growth and metabolism in anaerobic acidification pretreatment, meeting the common matrix nutritional conditions for anaerobic microorganisms to degrade refractory organic matter. After coking wastewater is pretreated by anaerobic acidification, it can improve the aerobic biodegradation performance of refractory organic matter and create good conditions for subsequent aerobic biological treatment. Zhao Jianfu et al. used hydrolysis-acidification as a pretreatment process for coking wastewater. After 6 hours of hydrolysis-acidification and 12 hours of aerobic biochemical treatment, the COD removal rate reached 91%, which was nearly 40% higher than the traditional biochemical treatment method. 2 Secondary treatment technology of coking wastewater After pretreatment of coking wastewater, the biodegradability of the wastewater has been improved, but the refractory organic matter cannot be completely decomposed into CO2 and H2O, so secondary treatment must be performed. There are many secondary treatment methods for coking wastewater, including biochemical methods, physical methods, chemical methods, and physicochemical methods. At present, the secondary treatment technologies with good results mainly include the following. 2.1 Catalytic wet oxidation technology Catalytic wet oxidation technology is a new technology developed internationally in the 1980s to treat high-concentration organic wastewater. It uses air oxidation under a certain temperature and pressure under the action of a catalyst to oxidize and decompose organic matter and ammonia in the wastewater into harmless substances such as CO2, H2O and N2, respectively, to achieve the purpose of purification. It is characterized by high purification efficiency, simple process and small floor space. Du Hongzhang et al. developed a wet oxidation catalyst suitable for treating steamed ammonia in coking plants and concentrated coking wastewater before dephenolization. The catalyst has high activity, resistance to acid and alkali corrosion, high stability, and is suitable for industrial applications. The removal rates of CODcr and NH 3 -N are 99.5% and 99.9% respectively. ； Moreover, based on the results of a small trial of the catalytic wet oxidation method to treat coking wastewater, it is estimated that the treatment cost is similar to that of the biochemical method, but the treated water quality is far better than the biochemical method. From the analysis of technical, economic indicators and environmental benefits, it is economically feasible to use catalytic wet oxidation method to treat coking wastewater. 2.2 Bioaugmentation technology Bioaugmentation technology refers to adding microorganisms with specific functions into the biological treatment system to improve the treatment effect of the original treatment system. The added microorganisms can be derived from the original treatment system and added after being acclimated, enriched, screened, and cultured to a certain number, or they can be exogenous microorganisms that did not originally exist. Both methods are used in practical applications, mainly depending on the composition of microorganisms in the original treatment system and the environment. This technology can give full play to the potential of microorganisms and improve the biological treatment effect of refractory organic matter. Selvaratnam et al. improved the phenol removal rate by adding the phenol-degrading bacteria Psendomonas Pvotida ATCC11172 to the activated sludge. The system maintained a phenol removal rate of 95%-100% within 40 days. In the control group without bioaugmentation, the phenol removal rate was initially very high, but soon dropped to about 40%. 2.3 Fanton reagent technology Fanton reagent is very effective in destroying organic molecules. Its essence is that the chain reaction between ferrous iron ions and hydrogen peroxide catalyzes the generation of •OH radicals. The ferric ion catalyst (called Fanton type reagent) can also stimulate this reaction. The •OH radicals generated by these two reactions can effectively oxidize various toxic and difficult-to-treat organic compounds. ； Or use an ultraviolet lamp as a radiant energy source to emit ultraviolet rays into the wastewater. When the hydrogen peroxide is activated by ultraviolet light, the reaction product is a highly reactive •OH radical. This •OH group quickly triggers an oxidation chain reaction, and eventually the organic compound is decomposed into CO2 and H2O. K. Banerjeek et al. experimentally proved that: Both treatment processes, using hydrogen peroxide to add iron salts and using ultraviolet light, hydrogen peroxide and catalysts at the same time, can effectively reduce the COD concentration in coking wastewater. 2.4 Immobilized cell technology Immobilized cell (IMC) technology is a method that uses chemical or physical means to locate free cells or enzymes in a limited spatial area so that they can remain active and can be used repeatedly. Immobilized cells can be prepared by adsorption methods, covalent binding methods, cross-linking methods, embedding methods, etc. Immobilized cell technology gives full play to the degradation potential of efficient bacterial strains or genetically engineered bacteria in degrading organic matter. This technology is characterized by high cell density, rapid reaction, low microbial loss, easy product separation, easy control of the reaction process, low sludge production, and can remove nitrogen and high-concentration organic matter or certain refractory substances. Amanda et al. used PVA-H3BO3 embedding method to immobilize Pseudomonas and ran it continuously in a fluidized reactor for 2 weeks. The inlet water phenol concentration gradually increased from 250mg/L to 1300mg/L, and the effluent phenol concentration was all 0. 2.5 Three-phase gas lifting circulating fluidized bed Cai Jian'an has been proved by experimental research: The use of three-phase gas lifting internal circulating fluidized bed reactor (AZLR) to treat coking wastewater is better than the activated sludge method. Its treatment load is high, the COD inlet water load is 13kg/(d·m 3 ), and the volumetric load of COD removal can reach 7kg/(d·m 3 ). It has strong tolerance to phenol, cyanide and other pollutants, good removal effect, and low aeration energy consumption. Its COD removal rate is 54.4% to 76%, the phenol removal rate is 95% to 99.2%, and the cyanide removal rate is 95% to 99.2%. 2.6 Anoxic-Aerobic-Contact Oxidation Method In this process, the dissolved oxygen is controlled below 0.5 mg/L during the anoxic process. The facultative denitrifying bacteria use the COD in the incoming water as a hydrogen donor to reduce the nitrate and nitrite in the aerobic pool mixed solution to generate ammonia and discharge it into the atmosphere. At the same time, the acid production process during the anaerobic biological treatment reaction is used to decompose some complex macromolecular condensed ring compounds into low molecular organic matter. In the aerobic process, when the dissolved oxygen is in the range of 3 to 6 mg/L, carbonizing bacteria in the aerobic pool first degrade easily degradable carbon compounds, and then nitrite bacteria and nitrate bacteria oxidize ammonia nitrogen. ； During the contact oxidation process, the dissolved oxygen is controlled at 2 to 4 mg/L, which can further degrade refractory organic matter and remove ammonia nitrogen and phosphorus, which plays a key role in water quality. Linfen City Coal Gasification Company in Shanxi Province adopts this process. The effluent water quality changes from COD 3000mg/L, ammonia nitrogen 650mg/L, and phenol 250mg/L before treatment to 140mg/L, 230mg/L, and 0.9mg/L respectively after treatment, which is basically close to the "Integrated Wastewater Discharge Standard". 3. Coking wastewater advanced treatment technology COD and NH 3 -N in the secondary effluent of coking wastewater often exceed the standard, so tertiary treatment should be carried out. Many scholars have developed some three-stage treatment methods, such as chemical oxidation, breakpoint chlorination, flocculation and sedimentation supplemented by chlorination, adsorption filtration supplemented by ion exchange, etc. However, due to economic and technical reasons, these methods are all in the experimental stage. Currently, there are two main types of three-stage treatment methods that are more economically feasible. 3.1 Oxidation pond deep treatment method Oxidation pond deep treatment of coking wastewater is simple and easy to implement, has good treatment effect, low energy consumption, easy management and low cost. The COD inlet water concentration is in the range of 250-400mg/L, and this method has an ideal COD treatment effect. The suitable pH value for the oxidation pond to treat low-concentration coking wastewater is 6-8, and the optimal pH value is 7 ； The suitable temperature range is 25-35℃, and the optimal temperature is 35℃. If domestic sewage is added to coking wastewater, the COD and NH 3 -N removal rates can be improved. Algae absorption is the main way to remove NH 3 -N in the oxidation pond of coking wastewater, and nitrification reaction is an important reaction in the conversion of NH 3 -N in coking wastewater. Wu Hongwei and others have proven through experiments that using oxidation ponds to deeply treat coking wastewater can achieve emission standards for COD and NH 3 -N. 3.2 The results of X-ray diffractometer measurement using fly ash adsorption method show that: The main components of fly ash are SiO 2 , Al 2 SO 5 , NaAlSiO 4 , etc. Fly ash is used as an adsorbent to deeply treat coking wastewater. It has good decolorization effect, good removal effect on CODcr, volatile phenol, oil, etc., and is low cost. Studies by Zhang Zhaochun and others have shown that humic acid substances-Changyan coal as an adsorbent have a fast adsorption rate and considerable adsorption capacity for chemical oxygen-consuming substances in coking wastewater, and can carry out advanced treatment of coking wastewater. Shanxi Coking Plant adopts biochemical-fly ash deep treatment technology for coking wastewater. After treatment, in addition to high ammonia nitrogen, the concentrations of CODcr, volatile phenols, sulfides, cyanides, BOD5 and other pollutants are all lower than * * According to the prescribed allowable discharge standards, 60% of the treated water is reused. 4 Conclusion In-depth research on the advanced treatment technology of coking wastewater is not only a practical problem faced by the current economic construction, but also the focus of future technological research. We should seek efficient and economical treatment technology to improve environmental quality and realize the recycling of water resources.