Lack of data for coking design

1. Reference materials for coking design; 2. Actual data from the site; 3. Papers from various journals as references; 4. Data and materials from industry associations and related conferences as references. Field visits are necessary for 2, 3, and 4.

1. Refer to the design references for coking plants. 2. Take into account the actual parameters and requirements on site. 3. Understand the situation in the same industry. 4. Visit similar coking enterprises in person

I’ll post a few books related to coking processing here for you to study a bit. 1. “Construction, Heating-up, and Commissioning of Coking Ovens” http://bbs.hcbbs.com/thread-156644-1-2.html 2. “Practical Handbook of Coking Chemical Engineering” http://bbs.hcbbs.com/thread-32948-1-1.html 3. “Coking Production Process Technology” http://bbs.hcbbs.com/thread-170150-1-1.html 4. “Fundamentals of Coal Chemical Engineering” http://bbs.hcbbs.com/thread-173538-1-2.html 5. “Practical Handbook on Operational Skills and Safety Management for Frontline Workers in Coking Enterprises” http://bbs.hcbbs.com/thread-124195-1-2.html 6. “Reference Materials for Coking Design” http://bbs.hcbbs.com/thread-3934-1-2.html 7. “Coal Chemistry” http://bbs.hcbbs.com/thread-171848-1-2.html 8. “Compilation of Information on the Coal Tar Industry” http://bbs.hcbbs.com/thread-106220-1-2.html

What was said on the fourth floor is right; as beginners, we should learn more*, right?

Is there a design manual for coking wastewater?

Addressing the environmental pollution caused by coking wastewater. Article abstract: Coking wastewater is generated during the high-temperature carbonization of coal, as well as in the processes of gas purification and chemical product refinement. It contains dozens of pollutants such as phenols, ammonia nitrogen, cyanides, benzene, pyridine, indole, and quinoline. This wastewater has a complex composition, with high concentrations of pollutants, a high color intensity, and strong toxicity; its properties are very stable, making it a typical example of organic wastewater that is difficult to degrade. Its excessive emissions pose a serious threat to humans, aquatic life, and crops. How to improve and address the environmental pollution caused by coking wastewater has become an urgent issue that needs to be resolved. 　　Currently, coking wastewater is generally pre-treated using conventional methods, followed by secondary treatment via biological dephenolization. However, even after the aforementioned treatment of coking wastewater, it remains difficult for parameters such as cyanide, COD, and ammonia nitrogen in the discharged wastewater to meet the required standards. In response to this situation, scholars at home and abroad have carried out... Coking wastewater is generated during the high-temperature carbonization of coal, as well as in the processes of gas purification and chemical product refinement. It contains dozens of pollutants such as phenols, ammonia nitrogen, cyanides, benzene, pyridine, indole, and quinoline. Its composition is complex; the concentrations of pollutants are high, its color intensity is high, and it is highly toxic. Moreover, it is very stable in nature, making it a typical type of refractory organic wastewater. Its excessive emissions pose a serious threat to humans, aquatic life, and crops. How to improve and address the environmental pollution caused by coking wastewater has become an urgent issue that needs to be resolved. 　　Currently, coking wastewater is generally pre-treated using conventional methods, followed by secondary treatment via biological dephenolization. However, even after the aforementioned treatment of coking wastewater, it remains difficult for parameters such as cyanide, COD, and ammonia nitrogen in the discharged wastewater to meet the required standards. In response to this situation, scholars at home and abroad have conducted extensive research in recent years, identifying many relatively effective treatment technologies for coking wastewater. These methods can be roughly divided into four categories: biological methods, chemical methods, physicochemical methods, and recycling. 　　1 Biological treatment method The biological treatment method is a technique that uses microorganisms to oxidize and decompose organic substances in wastewater, and it is often used as the secondary treatment stage in coking wastewater treatment systems. Currently, the activated sludge process is the most widely used aerobic biological treatment technology for coking wastewater. This method involves allowing biological flocs and activated sludge to come into full contact with the organic matter in the wastewater ； Soluble organic matter is absorbed and adsorbed by cells, and ultimately oxidized into end products (mainly CO2). Insoluble organic matter is first converted into soluble organic matter, and then metabolized and utilized. The basic process is shown in Figure 1. 　　 　　Figure 1: Basic process of biological treatment. However, with this technology, it is difficult to meet the standards for pollutants such as CODCr, BOD5, and NH3-N in the effluent; in particular, there is almost no degradation of NH3-N. In recent years, bioenhancement technologies have been developed by focusing on microorganisms, reactors, and process flows, including biological fluidized beds, immobilized biological treatment technologies, and biological nitrogen removal technologies. The development of these technologies has enabled the biodegradation of most organic substances, significantly improving the quality of the treated water, which has made biological treatment a highly promising wastewater treatment technique. The coking plants of Hefei Iron and Steel Group Company, Anyang Iron and Steel Company, and Kunming Coking and Gas Production Plant employ the A/O (anoxic/oxidative) biological nitrogen removal process. Operational results show that this process is stable and reliable, and it achieves good wastewater treatment effects; however, it requires large-scale treatment facilities and results in high investment costs. Shanghai Baosteel Coking Plant has replaced its original A/O biological nitrogen removal process with the A/OO process; the wastewater treatment efficiency is better than that of the A/O process, the operating costs have been reduced, and the benefits are evident. 　　Overall, biological methods have advantages such as the ability to treat large volumes of wastewater, a wide range of applicable waste streams, and relatively low operating costs. Improved new technologies have enabled the treatment of coking wastewater to meet engineering application requirements, which has led to the widespread adoption of this technology both domestically and internationally. However, the biodegradation method requires large amounts of dilution water, large-scale treatment facilities, long retention times, and high investment costs. It also has strict requirements regarding the quality of the wastewater; various factors such as the pH value, temperature, nutrients, concentration of toxic substances, organic matter content in the wastewater, and dissolved oxygen level can all affect bacterial growth and the quality of the treated water. This, in turn, imposes high demands on operational management. 　　2 Chemical treatment methods 　　2.1 Catalytic wet oxidation technology 　　Catalytic wet oxidation technology involves the use of oxygen from the air, under high temperature and pressure conditions and with the aid of catalysts, to oxidize organic substances that are dissolved in water or suspended in it, converting them into harmless substances such as N₂ and CO₂ that can be released. Research on this technology began in the 1970s, evolving from Zimmerman’s wet oxidation technique. In our country, Anshan Coking and Refractory Research Institute, in collaboration with the Dalian Institute of Physical Chemistry of the Chinese Academy of Sciences, has successfully developed a two-component, highly active catalyst that exhibits excellent performance in treating coking wastewater containing high concentrations of ammonia nitrogen and organic substances. 　　The wet catalytic oxidation method has advantages such as a wide range of applicability, fast oxidation speed, high treatment efficiency, low secondary pollution, and the ability to recover energy and useful materials. However, due to the high cost of its catalysts, high treatment costs, the need to operate under high temperature and pressure conditions which imposes strict requirements on process equipment, and high investment costs, this method is rarely used for wastewater treatment in China. 　　2.2 Incineration method The use of incineration to treat wastewater began in the 1950s. This method involves spraying the wastewater in the form of a mist into a high-temperature combustion furnace, where the mist vaporizes completely. The organic substances in the wastewater are then oxidized within the furnace, breaking down into fully burned products such as CO₂ and H₂O, along with a small amount of inorganic ash. 　　Coking wastewater contains large amounts of NH3-N. During combustion, NO is generated from NH3, and whether the formation of NO leads to secondary pollution is a critical issue when using incineration to treat coking wastewater. Through their research, Yang Yuanlin and colleagues found that under non-catalytic oxidation conditions, the main product of NH3 is N2, and no high concentrations of NO are generated, thereby avoiding secondary pollution. This shows that the incineration treatment process is a practical method for treating high-concentration wastewater from coking plants. However, despite its high treatment efficiency and lack of secondary pollution, the high treatment cost (around $167 per ton) deters most companies, resulting in its limited use in our country. 　　2.3 Ozonation method Ozone is a strong oxidizing agent that can rapidly react with most organic substances and microorganisms present in wastewater. It enables the removal of pollutants such as phenols and cyanides from wastewater, reduces its COD and BOD values, and also serves to decolorize, deodorize, and sterilize the water. 　　Ozone’s strong oxidizing property enables the rapid and effective removal of pollutants from wastewater. Moreover, ozone decomposes quickly into oxygen in water, thus avoiding secondary pollution, and its operation and management are simple and convenient. However, this method also has disadvantages such as high investment costs, high power consumption, and high treatment costs. At the same time, if not used properly, ozone can cause harm to surrounding organisms. Therefore, at present, the ozone oxidation method is still mainly used for the advanced treatment of wastewater. Ozone oxidation is being used in the United States to treat coking wastewater. 　　2.4 Plasma treatment technology Plasma technology utilizes the combined effects of high-energy electrons (5–20 eV) and ultraviolet light generated by high-voltage nanosecond pulse discharges to degrade organic substances in wastewater. Plasma treatment technology is a new type of environmentally friendly technology that is efficient, low-energy-consuming, widely applicable, and capable of handling large volumes of material; it is still in the research phase at present. Studies have shown that in coking wastewater treated with plasma, the large organic molecules are broken down into smaller ones, thereby **increasing** their biodegradability. Following treatment with the activated sludge method, the levels of phenol, cyanide, and COD in the effluent are significantly reduced, indicating good prospects for this approach. However, the cost of treatment devices is high, and further research and development of inexpensive treatment devices are needed. 2.5 Photocatalytic oxidation method: The photocatalytic oxidation method involves reactions between electrons and holes driven by light energy, resulting in electron (hole) pairs with high reactivity. These electron (hole) pairs migrate to the surface of the particles, where they can participate in and accelerate redox reactions. The photocatalytic oxidation method achieves a high removal rate for phenols and other organic substances in water. Gao Hua and others added catalyst powder to coking wastewater and introduced air under ultraviolet light, which enabled the effective removal of all organic toxins and colors from the coking wastewater. Under the optimal photocatalytic conditions, by controlling the wastewater flow rate at 3600 mL/h, the COD value of the effluent can be reduced from 472 mg/L to below 100 mg/L, with no polycyclic aromatic hydrocarbons detected. 　　At present, this method is still only at the theoretical research stage. This water treatment method can effectively remove pollutants from wastewater with low energy consumption, and it holds great potential for development. However, sometimes some harmful photochemical products are generated, causing secondary pollution. Since photocatalytic degradation is based on the system’s absorption of light energy, it is required that the system have good light transmittance. Therefore, this method is suitable for systems with low turbidity and good light transmittance, and can be used for the advanced treatment of coking wastewater. 　　2.6 Electrochemical oxidation technology The basic principle of electrochemical water treatment technology is to cause direct electrochemical reactions of pollutants at the electrodes, or to utilize the highly oxidizing substances generated on the electrode surface to induce redox transformations in the pollutants. Current research indicates that electrochemical oxidation possesses strong oxidizing capacity, a simple process, and does not cause secondary pollution, making it a wastewater treatment technology with considerable potential. 　　Chang et al. used PbO2/Ti as an electrode to degrade coking wastewater. The results showed that after 2 hours of electrolysis, the COD value decreased from 2143 mg/L to 226 mg/L, while 760 mg/L of NH3-N was also removed. The study also found that the electrode material, chloride concentration, current density, and pH value have a significant impact on both the COD removal rate and the current efficiency during the electrochemical reaction process. 　　Liang Zhenhai et al. used Ti/SnO2+Sb2O3+MnO2/PbO2 to treat coking wastewater, achieving a phenol removal rate of 95.8%. Its electrocatalytic performance is superior to that of Pb electrodes, allowing for a 33% reduction in energy consumption compared to Pb electrodes. 　　2.7 Chemical coagulation and flocculation Chemical coagulation and flocculation are used to remove fine suspended particles and colloidal particles that are difficult to eliminate through natural sedimentation in wastewater, thereby reducing the turbidity and color of the wastewater. However, they are ineffective against soluble organic substances, and are often employed for the advanced treatment of coking wastewater. This method has low treatment costs, and can be used either intermittently or continuously. 　　The key to coagulation methods lies in the coagulant. Currently, polyferric sulfate is commonly used as a coagulant; it is effective in removing CODCr, but less effective in removing color and F-. Lu Jianhang and others from the Institute of Environment at Zhejiang University have developed a specialized coagulant for the coking wastewater generated by Shanghai Baosteel Group. The experimental results showed that the optimal effective dosage of the coagulant is 300 mg/L, and the optimal coagulation pH range is 6.0–6.5 ； Coagulants achieve high removal rates for CODCr, F-, color, and total CN in coking wastewater; the removal efficiency is less affected by fluctuations in water quality. The coagulation pH has a significant impact on the removal efficiency of these various parameters. 　　Coagulants rapidly coagulate, adsorb, and agglomerate organic colloidal particles in wastewater, thereby enabling more effective advanced treatment of coking wastewater. Under the same conditions, Ma Yingge and others treated coking wastewater using three commonly used polysilicate flocculants (PASS, PZSS, PFSC) and sodium ferrate (Na2FeO4). The experimental results showed that sodium ferrate possesses excellent decolorization capabilities, as well as good performance in removing COD and turbidity. The flocculants it forms are small in size, few in number, settle rapidly, and do not cause secondary pollution. 　　3 Physicochemical methods 　　3.1 Adsorption method 　　The adsorption method is a technique that uses adsorbents to remove pollutants. 　　Activated carbon possesses excellent adsorption properties and stable chemical characteristics, making it the most commonly used adsorbent. The activated carbon adsorption method is suitable for the advanced treatment of wastewater. However, due to the high operational difficulty of the activated carbon regeneration system and the high operating costs, it has not been widely adopted in the treatment of coking wastewater. Shanghai Baosteel introduced a three-stage treatment process for coking phenol-cyanide wastewater from Japan in 1981, but did not install a third stage of activated carbon adsorption units in the second phase of the project; one of the reasons for this is as mentioned above. 　　Shanxi Coking Group Co., Ltd. uses boiler fly ash to treat coking wastewater from biochemical processes. After treatment with fly ash adsorption, the average removal rate of pollutants in the biochemical wastewater discharge was 54.7%. The treated effluent meets the standards for new coking plants at **Grade 1** for all pollutant parameters except ammonia nitrogen; it is similar to the A/O process, yet its investment cost is only half that of the A/O process. This method has relatively low system investment and operating costs; it utilizes waste to treat other waste, offering good economic and environmental benefits. However, it also has the disadvantages of untreated effluent containing ammonia nitrogen that does not meet standards, and difficult-to-treat waste residues. 　　Liu Junfeng et al. used high-temperature slag filtration followed by adsorption treatment with Nankai brand H-103 macroporous resin to treat coking wastewater containing 520 mg/L of phenol and 3200 mg/L of COD. The effluent after treatment had a phenol content of ≤0.5 mg/L and a COD level of ≤80 mg/L, meeting the **discharge standards. Huang Niandong et al. studied the purification effect of fine cokereast on coking wastewater. They investigated the effects of various factors such as particle size, pH, and solution flow rate on the adsorption capacity. The results showed that for a liquid containing 30 mg/L of phenol, the removal rate of phenol was 98% at a flow rate of 4.5 mL/min, a pH of 2–2.5, and a temperature of 25°C. 　　3.2 Utilizing flue gas to treat coking wastewater The “Method for treating residual ammonia water from coking or all coking wastewater using flue gas,” developed through collaboration between the Building Research Institute of the Ministry of Metallurgical Industry and Beijing Guoweeda Environmental Protection Company, has been granted a **patent**. This technology removes tar and SS from the coking residual ammonia water, then introduces it into flue gas to undergo thorough physical and chemical reactions. The heat in the flue gas causes all the water in the residual ammonia water to vaporize, and the ammonia reacts with SO2 in the flue gas to produce ammonium sulfate. 　　This patented technology has been successfully applied in the treatment of residual ammonia water from coking processes at Jiangsu Huaiyang Iron and Steel Group. Monitoring results show that all the residual ammonia water from coking was treated, achieving zero discharge of wastewater, while also ensuring that flue gas emissions met regulatory standards. The main pollutants discharged into the atmosphere, such as ammonia, phenols, and cyanides, accounted for 1.0% to 4.7% of the total amount of pollutants in the residual ammonia water. 　　This method uses waste to treat waste, requires low investment, occupies little space, has low operating costs, delivers good treatment results, and offers significant environmental benefits; it is therefore a method highly worthy of promotion. However, this method requires that the amount of ammonia used in coking be balanced with the amount of ammonia needed in the flue gas, which limits the applicability of this method to a certain extent. 　　4 Waste water recycling: High-concentration coking wastewater is dephenolized, and after solid precipitates and light tar are removed, it is sent to the coke ovens for coke quenching, thereby achieving a closed-loop circulation of phenol-containing water. This reduces waste discharge and lowers operating costs, etc. >. However, the issue of pollutant transfer at this time is also worth considering. 　　5 Conclusion The successful application of technologies for treating coking wastewater is primarily constrained by three factors: treatment efficiency, investment and operating costs, and the potential for causing secondary pollution. Current governance technologies are not yet able to fully meet the requirements in these three areas. Each of them has its advantages and disadvantages; therefore, it is necessary to choose technical methods that suit one’s own characteristics based on the specific circumstances, as well as to combine existing methods in an organic way in order to achieve satisfactory results. At the same time, it is necessary to further research and develop new technologies that offer better treatment results, lower investment and operating costs, no secondary pollution, and are easy to operate and manage. Only in this way can they better suit the national conditions and have broader prospects for development. 　　References
1. Mao Tihe. Chemical Waste Water Treatment Technologies. Beijing: Chemical Industry Press, 2000. 169
2. Wei Guorui, Li Guoliang. Exploration of New Processes for Treating Coking Waste Water at Baosteel. Fuel & Chemical Engineering, 2001, (1): 34–36
3. Yin Chenglong, Shan Zhongjian. Problems in Coking Waste Water Treatment and Corresponding Solutions. Industrial Water Supply and Drainage, 2000, 26(6): 35–37
4. Yang Yuanlin, Zhou Yunwei. Discussion on Treatment Processes for High-Concentration Coking Waste Water. Mechanical Management & Development, 2001, 64(4): 41–42
5. Arana J, Tello Rendon E. Treatment of High-Concentration Phenolic Waste Water via Photo-Fenton Reaction: Mechanism Study Using FTIR-ATR. Chemosphere, 2001, 44(5): 1017–1023
6. Xu Xinhua. Handbook on Treatment of Specific Pollutants in Industrial Waste Water. Beijing: Chemical Industry Press, 2000. 185
7. Zhang Yu, Jiang Bairu. Research on Treatment Technologies for Coking Waste Water in the Iron and Steel Industry. Industrial Safety and Environmental Protection, 2002, 28(7): 5–7
8. Sun Dezhi. Advanced Oxidation Technologies in Environmental Engineering. Beijing: Chemical Industry Press, 2002. 277
9. Gao Hua, Liu Kun. Study on the Treatment of Organic Toxins in Coking Waste Water Using Ultraviolet Photocatalytic Oxidation. Journal of Qingdao Medical University, 1996, 32(3): 203–206
10. Chiang L C, Chang J E. Electrochemical Oxidation Process for the Treatment of Coke-Plant Waste Water. J Envir. Sci. Health, 1995, 30(4): 753–771
11. Liang Zhenhai, Xu Wenlin. Oxidation Treatment of Phenol-Containing Coking Waste Water on Ti/PbO2 Electrodes. Rare Metal Materials and Engineering, 1996, 25(3): 37–40
12. Lu Jianhang, Wang Hongbin. Removal Efficiency and Patterns of Pollutants by Special Coagulants Used in Coking Waste Water Treatment. Environmental Science, 2001, 21(7): 65–68
13. Liu Cuihua, He Xuanming. Application of Coagulants in the Re-purification of Coking Waste Water. Journal of Wuhan University of Metallurgy and Technology, 1999, 22(1): 42–45
14. Ma Yingge, Zhang Qingyou. Study on the Treatment of Coking Waste Water Using Different Coagulants. Environmental Pollution and Control, 2002, 24(1): 16–18
15. Zhang Changming. Research on Purification and Reuse Technologies for Coking Waste Water. Environmental Engineering, 1999, 17(1): 16–19
16. Liu Junfeng, Yi Pinggui. Study on the Treatment of Coking Waste Water Using Filtration-Resin Adsorption Method. Coal Chemistry, 2002, 100(3): 59–62
17. Huang Niandong, Xia Changbin. Study on the Adsorption of Phenol in Waste Water by Fine Coking Slag. Journal of Xiangtan Institute of Mining, 2000, 15(2): 63–66
18. General Research Institute of Building Technology, Ministry of Metallurgical Industry, and Beijing GuoweiDa Environmental Protection Company. Methods for Treating Residual Ammonia Water or All Coking Waste Water from Flue Gas. China: 98101337.6, 1998-04-08
19. Cheng Zhijiu, Yin Guangjin. Research on the Treatment of Residual Ammonia Water from Flue Gas in Coking Processes. Acta Scientiae Circumstantiae, 2000, 20(5): 639–641
20. Zhou Guocheng. Treatment of Coking Waste Water. Chemical Water Supply and Drainage Design, 1995, 4: 9–14

Coking wastewater treatment engineering technology (I) Project overview 1. Wastewater quality: The project currently has a treatment unit with a capacity of 200 m3/day, and renovation is required； In addition, the second phase of the project, which is to be put into operation shortly, will involve the construction of a new wastewater treatment system capable of handling 200 m3/day of wastewater, bringing the total wastewater volume to 400 m3/day. Table 1 – Quality parameters of coking wastewater (units: mg/L)
Pollutant indicators: CODCr, NH3-N, SS, pH; Remarks: Raw wastewater values are 3500, 200, 330, and 9 respectively.

2. Wastewater discharge standards
In accordance with the second-level standards of Shanghai’s comprehensive wastewater discharge regulations, the discharge standards that must be met after wastewater treatment are shown in Table 2:

Table 2 – Discharge standards for treated wastewater (except for temperature and pH, all other values are in mg/L)
Pollutant indicators: CODCr, NH3-N, SS, pH; Remarks: Discharge standards are 150, 25, 200, 6–9, and 0.5 respectively.

(II) Wastewater treatment process
1. Process flow
Based on the results of wastewater treatment at Shanghai Coking Co., Ltd., and taking into account the existing treatment processes, this project adopts the A1–A2–O biofilm process. Efforts should be made to avoid altering the function and structure of existing wastewater treatment facilities, making full use of the treatment capacity of these existing structures. The old system should be upgraded by adding an anaerobic acidification tank to the existing A/O system, thereby converting it into an A1-A2-O biological treatment system. A new set of A1–A2–O biochemical systems will be installed, with each of the two sets handling half of the total water treatment volume. 2. Process flow description: (1) The production wastewater and domestic sewage generated in various workshops are all directed to a regulating tank. The main function of this tank is to balance the quality and quantity of the wastewater, thereby ensuring the stable operation of the subsequent biochemical treatment facilities. Since the wastewater contains very little phosphorus, phosphorus nutrients are added to the equalization tank to provide the nutrition required by microorganisms. (2) The wastewater coming out of the regulation tank is pumped by two pumps to the new and old A1–A2–O biochemical treatment systems respectively. In these biochemical treatment systems, the degradation process of the wastewater proceeds as follows: a. The coking wastewater first enters the anaerobic acidification stage. In this section, phenol, xylene, as well as heterocyclic compounds such as quinoline, isoquinoline, indole, and pyridine in the wastewater were significantly transformed or removed; the presence of an anaerobic acidification stage is highly beneficial for the transformation and removal of complex organic substances. Therefore, after passing through the anaerobic acidification stage, the quality of the wastewater improves significantly; its biodegradability increases compared to that of the raw water, providing an effective carbon source for the subsequent denitrification stage. b. The main reaction that takes place in the anoxic zone is denitrification. The wastewater coming out of the aerobic zone enters the anoxic zone, and at the same time, a portion of the water treated in the aerobic zone is also recycled back to the anoxic zone to supply nitrate nitrogen there. Furthermore, due to the insufficient denitrification carbon source in the coking wastewater, methanol must be added to the anoxic tank as a supplementary carbon source. After passing through the anoxic section, nitrate nitrogen is converted into nitrogen gas, achieving denitrification. At the same time, most of the organic matter in the wastewater is removed, allowing the wastewater to enter the aerobic stage with a lower COD level, which is highly beneficial for the nitrification reactions that take place in this stage. c. The wastewater enters the aerobic stage after being treated in the anoxic stage. In the aerobic stage, the ammonia nitrogen content in the wastewater is high while the COD is low. Therefore, the main reaction that takes place here is nitrification, and an soda ash solution must be added in the aerobic section to provide the alkalinity required for this reaction. After being treated in the aerobic section, the ammonia nitrogen is almost completely converted into nitrate nitrogen (nitrate nitrogen is effectively removed by being recycled to the anoxic section, where it is ultimately converted into nitrogen gas); at the same time, the organic matter is further degraded, ensuring that the COD level of the final effluent meets the standards. (3) After being treated by the biochemical system, the wastewater passes through a coagulation and sedimentation tank for sludge-water separation. Polyferric salts are added during the coagulation stage to improve the sedimentation properties of the sludge and further reduce the COD level in the effluent. The effluent from the secondary sedimentation tank is fed into the “North Discharge” pipeline network. (4) The excess sludge discharged from the secondary sedimentation tank is periodically sent to a sludge thickening tank for thickening and stabilization. The supernatant from the thickening tank is returned to the adjustment tank for further treatment, while the sludge from the thickening tank is sent to a sludge storage tank, where it is periodically dehydrated using a sludge dewatering machine. Before dewatering, PAM must be added to carry out a flocculation reaction with the sludge in order to improve the efficiency of sludge dewatering. The sludge is dewatered and then transported for disposal. 4. Process conditions: (1) Control of wastewater quality and volume: Based on the original statistical data regarding the quality and volume of the wastewater generated in coking processes, as well as the requirements specified in the design plan, the quality and volume of the wastewater entering the wastewater treatment system must meet the design specifications. (2) Pretreatment of wastewater: To reduce the load on subsequent biochemical treatment processes, to mitigate the impact of toxic substances, and to ensure stable performance of these biochemical treatments as well as to facilitate operational management, wastewater needs to be pretreated before it enters the system. a. Control the COD level of the incoming water; large fluctuations in the COD level of the incoming water can have a significant impact on the operation of the system. Therefore, in accordance with the design requirements, the COD of the incoming water must be strictly controlled to remain within the specified range. b. Control the temperature of the incoming water: The final cooling wastewater from the old plant area, the ammonia evaporation wastewater, and the ammonia evaporation wastewater from coke ovens No. 5 and No. 6 have very high temperatures; therefore, they must be cooled to below 38°C using plate condensers and mist coolers before being discharged into the regulation tank. c. Controlling the oil content in the influent water: Gas condensation wastewater and turbid water from various sources are treated by gravity oil separation and air flotation to remove oil (reducing the oil content to below 30 mg/L), so that the oil concentration is below that which could affect the normal growth of microorganisms, after which it is discharged into the regulation tank. c. Reducing ammonia nitrogen: Some of the ammonia-containing wastewater is first passed through the ammonia fixation device provided by the coking company, which reduces its ammonia nitrogen concentration from 800 mg/L to 250 mg/L before it is discharged into the regulation tank. d. Reducing ash content: The wastewater from the tri-generation system contains a high amount of ash, so it must be settled to remove the ash before being discharged into the regulation tank. (2) Anaerobic acidification tank a. Design parameters: Design flow rate 210 m3/h, hydraulic retention time 5.6 h, effective contact time 5.0 h. b. Monitoring: Samples are taken three times a day to test the CODcr, NH3-N, oil content, and pH of the inlet and outlet water. The quality parameters of incoming and outgoing water are measured periodically: CODcr, BOD5, NH3-N, SS, phenols, cyanides, pH, oils, and water temperature. 3) Anoxic tank a. Design parameters: Design flow rate 210 m3/h, hydraulic retention time 10.5 h, effective contact time 9.1 h b. Methanol addition: The methanol addition is used to supply the carbon source required for denitrification. Operate the methanol dosing unit to adjust the dosage level, ensuring uniform distribution of the substance. Methanol is added at a rate of 0.46 kg per cubic meter of water, resulting in an addition concentration of 5%. a. Monitoring: Samples are taken three times a day to test the CODcr, NH3-N, and oil content in the inlet and outlet water. Water quality parameters of inlet and outlet water are measured periodically: CODcr, BOD5, NH3-N, SS, phenol, cyanide, pH, dissolved oxygen (DO), oils, and water temperature. (4) Contact oxidation tank a. Design parameters: Design flow rate 210 m3/h, hydraulic retention time 22.1 h, effective contact time 18.4 h. b. Soda ash addition: The function of adding soda ash is to supply the alkalinity required for nitrification and to maintain the pH between 7.5 and 8.2. Operate the soda ash dosing unit to adjust the dosage and meet the requirements for uniform distribution. Sodium carbonate is added at a rate of 1.081 kg per cubic meter of water, resulting in a concentration of 10%. c. Recirculation mixture flow control: The flow rate of the mixture from the contact oxidation tank to the anoxic tank is controlled by the recirculation pump. b. Monitoring: Samples are taken three times a day to test the CODcr, NH3-N, oil content, pH, NO2-N, and NO3-N of the inlet and outlet water. Water quality parameters of inlet and outlet water are measured periodically: CODcr, BOD5, NH3-N, SS, phenol, cyanide, pH, dissolved oxygen (DO), oils, and water temperature. 2. Commissioning of the individual processes in the new system: The newly built AAO biological treatment system features a steel ring-shaped integrated structure in terms of tank design. This structure integrates an anaerobic acidification tank, an anoxic tank, a contact oxidation tank, a coagulation tank, and a secondary sedimentation tank, thereby enhancing the plug-flow flow pattern of the wastewater. While ensuring the system’s ability to treat pollutants, it also provides the system with good stability as well as the capacity to withstand hydraulic shock loads, organic load shocks, and ammonia nitrogen load shocks. a. Design operating parameters (as shown in Table 4 – Design Operating Parameters for the New System)
Table 4: Design Operating Parameters for the New System

**Water Tank**
Design flow rate: 210 m3/h
Hydraulic retention time: 5.6 h
Effective contact time: 5.1 h

**Anoxic Acidification Tank**
Design flow rate: 210 m3/h
Hydraulic retention time: 9.4 h
Effective contact time: 8.5 h
Methanol added: Yes

**Aerobic Tank**
Design flow rate: 210 m3/h
Hydraulic retention time: 24.1 h
Effective contact time: 20.6 h
Soda ash added: Yes

**Mixing Tank**
Mixing time: 6 min
Reaction time: 27 min
Polyferric sulfate added: Yes

**Sedimentation Tanks (2 tanks)**
Flow rate per tank: 105 m3/h
Surface load: 0.8 m3/m2·h
Sedimentation time: 3.2 h

**Sludge Thickening Tank**
Capacity: 79 m3/d; Retention time: 30 h (per tank)

**Sludge Storage Tank**
Capacity: 79 m3/d; Retention time: 25.6 h (per tank)

Note: The methods and amounts of chemicals added to each tank are based on those used in the old system. b. Flow control of the recirculated mixture: Under normal operation in the anoxic tank, facultative microorganisms are present; these microorganisms grow and reproduce slowly under low-oxygen conditions, but they grow rapidly when the dissolved oxygen level is high. The flow rate of the mixture from the contact oxidation tank to the anoxic tank is controlled by the return water pump. c. Addition of polyferric sulfate in the coagulation sedimentation tank: The function of adding polyferric sulfate is to improve the sedimentation properties of the sludge. The dosing devices for iron salts and polyacrylamide are functioning properly, ensuring uniform dosing; 0.20 kg of ferric salt is added per cubic meter of water. d. Monitoring: Sample the inlet and outlet water three times a day to test CODcr, NH3-N, and oil content. Periodically measure various water quality parameters at the inlet and outlet of the anaerobic biological tank, anoxic tank, contact oxidation tank, and mechanically stirred sedimentation tank: CODcr, BOD5, NH3-N, SS, phenols, cyanides, pH, dissolved oxygen (DO), oils, and water temperature. Due to the large number of control parameters, the process coordination testing of automated systems focuses primarily on the key aspects of automatic control: a. Temperature monitoring. The biological treatment system for coking wastewater is designed based on the principle of using mesophilic bacteria to degrade organic matter. Either too high or too low temperatures can affect the metabolic functions of these bacteria and even lead to their death, thereby impacting the efficiency of wastewater treatment. Therefore, it is essential to strictly control and monitor the temperature of the wastewater fed into the biological treatment process. b. Monitoring of pH value and nitrate nitrogen: The biochemical rate of microorganisms is closely related to the pH value of wastewater. During the denitrification process of wastewater, different pH values can result in the formation of various forms of nitrate nitrogen (nitrite nitrogen and nitrate nitrogen) through microbial nitrification reactions. Nitrite has carcinogenic effects and has a significant impact on the quality of the treated water; therefore, its formation should be minimized as much as possible. Timely sampling is conducted to measure the concentrations of nitrite nitrogen and nitrate nitrogen at the end of the contact oxidation tank and in the anoxic tank, serving as one of the bases for adjusting process parameters such as the amount of methanol added and the oxygen supply. c. Monitoring of dissolved oxygen (DO) levels: The biofilm process relies on the high biochemical activity of aerobic microorganisms to remove organic pollutants, and the presence of dissolved oxygen in water is a necessary condition for the growth of these aerobic bacteria. Either too high or too low dissolved oxygen levels are detrimental to the treatment efficiency: too high levels cause sludge to age, resulting in reduced sedimentation properties and thus the occurrence of floating sludge in the effluent ； Insufficient oxygen supply leads to a decrease in the number of aerobic microorganisms in the tank, reduces the efficiency of biochemical treatment, and deteriorates the quality of the effluent water. An online dissolved oxygen meter in the contact oxidation tank is used to automatically control the oxygen supply amount. Timely sampling is conducted to measure the dissolved oxygen concentration in the anaerobic oxidation tank and the anoxic tank; at the same time, the biochemical efficiency is assessed based on the growth status of the microorganisms in the biofilm, with adjustments made as appropriate. d. Equipment operation monitoring: Real-time monitoring of the condition of key operational facilities and equipment. During operation, the dosage of soda ash is the highest. The chemical dosing is controlled in an automatic multi-point alkaline addition manner based on the pH values measured in the contact oxidation tank, which enables effective savings in chemical usage. The return flow rate of the mixed liquid also has a significant impact on the efficiency of denitrification. By adjusting this return flow rate according to the operating conditions of the anoxic tank, it is possible to ensure effective denitrification while simultaneously reducing the amount of chemicals required. To ensure uniformity and consistency in the regulating tank, automatic control is used to manage the operation of the pumps and the distribution of flow rates, thereby facilitating the operation and control of the subsequent treatment systems. Jigang Machinery Equipment Manufacturing Factory has developed an automatic high-pressure water cleaning device for furnace doors, enabling the automatic cleaning of coke oven doors. The high-pressure water automatic furnace door cleaning device uses a combination of high-pressure water and mechanical cutters for cleaning. The stainless steel knife edge and sealing groove are cleaned using high-pressure water (65 MPa), while the edges and bottom of the furnace door bricks are cleaned with a spiral milling cutter. This device is fully automatically controlled by PLC programming, and the cleaning time for one furnace door is approximately 5 minutes. By using this technology, the tar, coke, and other deposits on the refractory bricks of the coke oven doors as well as on the stainless steel edges can be completely removed, thereby ensuring the sealing between the oven doors and the main body of the coke oven and preventing the leakage of harmful gases and dust from inside the oven. At present, Jigang’s coking plant is already using this technology extensively on coke pushers and coke stoppers. 3. Coal loading dust control: When the coal loader feeds coal into the red-hot carbonization chamber, the evaporation of water in the coal and the rapid release of volatile components cause a sudden increase in pressure inside the chamber, resulting in large amounts of dust escaping from it. Currently, coking plants generally use sequential coal charging, install gas collection pipes, and employ high-pressure ammonia spray to create a negative pressure in the carbonization chamber in order to achieve smoke-free coal charging. However, the results are not entirely satisfactory. Due to the poor sealing performance of the coal loading sleeves, the sealing covers for the coal leveling rods, and the seats of the coal loading holes in most coal loading vehicles in the country, the suction force generated by the high-pressure ammonia spray varies greatly. As a result, the dust and smoke cannot be completely removed in a timely manner using the high-pressure ammonia spray, and a considerable amount of it escapes into the atmosphere through the coal loading holes and small furnace doors, causing environmental pollution. After the improvement of coal loading smoke and dust removal technology, there are mainly the following methods. (1) Dust removal method at the coal loading vehicle ground station: This method involves installing dust collection pipes, exhaust devices, and connectors on the coal loading vehicle. During coal loading, the gate valve of the dust removal main pipe at the ground is opened; a connector connects the dust collection pipeline on the coal truck to this main pipe. During the loading process, the large amount of smoke that escapes from the coal loading opening is drawn away by the high-pressure fan at the ground station through the dust removal main pipe, and it is then purified there. The removal efficiency of coal loading dust can reach around 95%. Currently, this method is widely used in China for controlling coal dust emissions. (2) Combination of pre-dust removal on the coal loading vehicle and treatment at the ground station: This approach consists of a coal loading vehicle equipped with incinerators and pre-washers, along with a ground-based purification station. The coal loading vehicle is equipped with no suction pumps or exhaust stacks; instead, the pre-washed and dehydrated dust is drawn through connecting valves and horizontal suction ducts to a ground station for final purification. After purification at the ground station, the coal dust removal rate can reach around 95%. Baosteel and Benxi Steel’s coking plants have successively adopted this method. (3) Coal loading dust removal without a ground station method: ① The coal loading vehicle is equipped with a washing device. During coal loading, the dust around the coal holes is drawn in from the smoke hood of the coal hopper on the loading vehicle, ignited for combustion, and then discharged into the atmosphere through the vehicle’s dust-removing and hydrocarbon-dehydrating extractor as well as the exhaust stack. ②Install the smoke exhaust connection pipe. The method of using connecting pipes to draw some of the flue gas from one carbonization chamber into an adjacent one is employed to achieve the purpose of reducing smoke and dust. ③Schalck controllable coal loading system. This system is a patented technology developed by the German company Schalke. Its principle is as follows: once the coal-loading tube and the coal-loading holes are hermetically connected, coal loading begins and the gas collection pipe is opened; all the coal-loading holes then load coal rapidly and controllably. The dust generated in the furnace creates a pressure excess, and when this excess pressure exceeds that of the gas collection pipe, the dust is discharged into it. Towards the end of the coal loading process, the high-pressure ammonia water injection device is activated. A controllable coal loading system can ensure the unobstructed flow of dust, without the need for leveling the coal or doing it once. ④On-vehicle dry dust removal coal loading method. The vehicle-mounted dry dust removal coal loading truck is a new type of coal loading truck jointly developed by Anshan Coking and Refractory Research Institute and Jigang Group. This technology integrates a dust removal system into the coal loading truck, which mainly consists of a bag filter, a pre-spraying device, a spark separator, a ash conveyor, a fan, and other components. It collects and purifies the dust that escapes from the coke oven during coal loading; the dust capture rate can reach 90%, while the dust removal and purification efficiency is greater than 99%. Currently, manufacturers such as Jigang, Kunsteel, and Xinxing Cast Pipe use this method. Due to its advantages such as low equipment investment, low operating costs, and excellent dust removal performance, this technology is particularly suitable for coke ovens that do not have the capability to establish on-site dust removal stations, as well as for environmental protection technology renovation projects. 4. Control of coke pushing dust: Coke pushing dust is one of the main sources of pollution caused by coke oven dust. In traditional coke pushing, blocking, and quenching operations, the equipment is open, resulting in a very harsh environment on the coke side. The main methods used domestically and internationally for controlling coke pushing dust currently include the following: (1) The Minister Stein-type movable dust collection hood combined with a ground-based purification system. This system was developed and put into use in the 1970s at the Minister Stein coking plant in Germany. The movable dust collection hood can cover the entire quenching car; one pivot is fixed on the quenching car, while the other pivot is on the third track, allowing the hood to move along with the quenching car. Dust and smoke enter the dust collection main pipe through the dust collection hood and belt cart, are sent to the ground station, and after being purified through wet washing, are released into the atmosphere. The coke pushing and dust removal system used in Japan is similar to the Minister Stein system, but it is equipped with high-efficiency bag filters, achieving a dust removal efficiency of over 95%. Additionally, the connection between the dust collection main pipe and the smoke hood uses flap valves rather than belt conveyors. In the 1980s, Baosteel fully adopted Japanese dust removal technology. In 1994, Shougang built a coke pushing and dust removal system at its No. 1 and No. 3 coke ovens by drawing on foreign technology and carrying out the design and installation work itself. This system utilized a belt-sealed main pipe connected to belt carts, and bag filters were employed; the dust content in the exhaust gas was 50–80 mg/h, with an average dust removal efficiency of 98.45%. The concentration of dust emitted into the atmosphere met the **emission standards. For coke pushing and dust removal at Jigang’s coke ovens No. 1, 2, 5, as well as the newly built ovens No. 6 and 7, the belt cart dust removal system based on the Shougang model is employed, and it has proven to be effective. (2) Thermal buoyancy hood dust removal vehicle: A dust removal vehicle designed to take advantage of the high temperature, low density, and buoyancy of the dust generated during coke pushing; it was first used in the Anna coking plant in Germany in the 1980s. One pivot of this vehicle is fixed to the coke car, while the other pivot is on the third track and moves along with the coke car. The lower part of the thermal buoyancy cover can cover 2/3 of the length of the coking quenching car. The dust emitted from the coking car enters the thermal buoyancy hood, where it is removed through two stages of water washing, and then is discharged into the atmosphere via the top of the hood ； The dust at the top of the focus guide grid and in the furnace door area is drawn in by a suction pump; after being washed with water and cleaned through cyclone separation, it is discharged into the atmosphere via an exhaust stack. Thermal buoyancy enclosure systems require fewer components, resulting in lower investment and operational costs. However, due to the limited dust removal capacity of the thermal buoyancy cover and its limited operational flexibility, the dust removal efficiency drops significantly when coking occurs or when the pressure used for water washing is insufficient, resulting in poor atomization. The actual dust removal efficiency is lower than that of the ground station purification system, typically ranging from 80% to 90%. 5. Coking quenching and dust removal technology: Currently, there are two methods for coking quenching in China, namely dry quenching and wet quenching. In 1998, Jigang built and put into operation two dry quenching units with a processing capacity of 70 t/h. The technology was imported from Ukraine, but the localization rate of the entire equipment exceeded 95%. Due to the well-developed dust removal system of the dry quenching unit, its operation brings significant benefits to both environmental protection and production. The first phase of Jigang’s 6m coke ovens is planned to adopt low-moisture quenching technology, which can reduce the moisture content in coke, improve its quality, simultaneously decrease the amount of water used for quenching, and lower the production costs of coke. In newly built wet quenching coke ovens in China, the use of a double-layer baffle capture section within the quenching tower prevents the steam used for quenching from carrying away coke dust and particulates, resulting in cost savings and rapid benefits. III. Conclusion: Large domestic coking enterprises have explored a successful path for comprehensive dust control by introducing foreign technologies, assimilating them, and driving innovation. By adopting technologies such as top-of-furnace dust control, high-pressure water cleaning of furnace doors, dry dust removal systems on coal loading vehicles, dust removal at the ground stations for coke pushing belts, and low-moisture coke quenching, Jigang has effectively controlled the leakage of dust during the mechanical operations of coke ovens and the coke production process. This has contributed to environmental protection as well as to the promotion of technologies and equipment for comprehensive dust management in coke ovens. References: 1. Cai Chengku, Zhang Xiaoguang, et al. Factors Affecting the Airtightness of Furnace Doors and Corresponding Improvement Measures. Fuel & Chemical Engineering, Vol. 34, No. 3, May 2003. 2. Liu Zhiping. Pollution Caused by Coke Oven Dust and Its Control Methods. Wugang Technology, No. 1, 1998. 3. Chan Xingdong, Wang Xianghong, Xia Pengfei, et al. Review of New Technologies Applied in Domestic Coke Ovens. Magang Technology, No. 2, 2002

Treatment technologies for phenol-containing wastewater: Phenol wastewater originates primarily from processes such as coking, gas production, oil refining, as well as chemical and pharmaceutical manufacturing that use phenol or phenolic resins as raw materials. It is widespread in occurrence, abundant in quantity, and highly harmful; it is considered one of the toxic and hazardous wastewaters that need to be addressed prioritarily in water pollution control efforts around the world. In the actual treatment of phenol-containing wastewater, for wastewater with high concentrations of phenol, the first step should be to consider recovering the phenol ； For wastewater with low phenol concentrations that has no value for recycling, or wastewater that still contains residual phenol after recycling processes, it is necessary to carry out harmless treatment to ensure compliance with discharge standards, thereby achieving a balance between economic and environmental benefits. The following will outline the research progress and development trends in the harmless treatment technologies for phenol-containing wastewater. Aerobic-anoxic process: The ability to biodegrade organic matter under aerobic or anaerobic conditions has certain limitations, but the use of an anaerobic-aerobic combined process leads to significant improvements. Treating coking wastewater using the anaerobic-anoxic/aerobic (A-A/O) process not only enables the removal of phenols, but also ensures that the COD and NH3-N levels in the effluent meet the specified standards; it represents an effective improvement over the conventional activated sludge method for treating coking wastewater. The anaerobic fixed-bed membrane-aerobic biological treatment process (i.e., the improved A/O process) is used to treat coking wastewater; by removing phenols and cyanides, it can significantly reduce pollutants such as COD and NH3-N, with results that are better than those achieved through aerobic biological treatment. Screening and cultivation of highly degrading microbial strains: Traditional biological methods mostly involve utilizing microbial populations that naturally occur in the environment after domestication and propagation; however, for toxic substances such as phenols, the degradation capacity of strains obtained from nature is usually limited. To this end, many scholars have carried out the screening and cultivation of highly degrading microbial strains. Some people used pure bacteria capable of degrading pentachlorophenol (PCP) to enhance the activity of sludge systems. By adding 5%–7% of such bacteria and increasing the PCP load to three times its original level, the PCP concentration in the effluent was stabilized within 18 hours, demonstrating good resistance to load shocks. Active sludge was directly conditioned using continuous-flow UV mutagenesis technology, and the results showed that conventional active sludge retained high degradation activity even at a phenol concentration of 1200 mg/L. Clearly, the introduction of highly degrading microbial strains can improve the degradation rate of phenolic wastewater. However, how to ensure that these superior strains remain dominant in the biological treatment system over the long term and maintain their high degrading activity is the main problem we need to address. Enzyme treatment technology: Enzymes are highly efficient and specific biological catalysts, and research on the use of enzyme technology for wastewater treatment began in the 1980s. There have been reports on the use of appropriate enzymes to catalyze the degradation of phenol-containing wastewater; for example, tyrosinase can achieve 100% degradation of phenol, while using horseradish peroxidase on wastewater containing 330 mg/L of phenol can result in a phenol removal rate of 97%–99%. However, water-soluble enzymes are used once and thus result in high treatment costs. The main problems to be solved for this are reducing costs and increasing enzyme activity. Immobilized cell technology: Over the past decade or so, research has been carried out both domestically and internationally on the use of immobilized cell technology for wastewater treatment, in order to overcome drawbacks such as the easy loss of microorganisms in the activated sludge process and the low tolerance of cells to toxins. By using red brick fragments as a carrier to immobilize the phenol-degrading bacteria, the maximum phenol tolerance of these bacteria can be increased from less than 180 mg/L for free cells to around 820 mg/L for immobilized cells. After immobilization, the reaction rate of these bacteria increases, thereby enhancing their ability to degrade phenol. Phenol can be completely degraded using a solid-phase cell membrane reactor constructed with the Pseudomonas putida strain 49451, even at concentrations as high as 2000–3500 mg/L; whereas Pseudomonas putida in suspension can only handle phenol at concentrations below 1000 mg/L. Immobilized cell technology is still in the research phase, and many challenges remain before it can be put into practical use. Oxidation treatment technology: Wet catalytic oxidation. This method involves adding an appropriate catalyst to the traditional wet oxidation process in order to reduce the reaction temperature and pressure, enhance the ability for oxidative decomposition, and shorten the reaction time. When used in combination with oxidants such as H2O2 and O3, the rate of free radical generation can be increased, further enhancing the wastewater treatment capacity. Using Cu(NO3)2 as a catalyst, wet oxidation was applied to treat coal gas wastewater containing phenol (7866 mg/L, COD 22928 mg/L), resulting in 100% removal of phenol, cyanide, and sulfur, as well as 65%~90% removal of COD. Although the wet catalytic oxidation method has a high efficiency in treating organic substances, it requires specialized equipment due to the reactions that take place under high temperature and pressure; such equipment must be able to withstand high temperatures, high pressures, and corrosion, and there is also significant catalyst loss. Therefore, studying catalysts that are efficient and economical under mild reaction conditions is an important issue to be addressed for the widespread application of wet catalytic oxidation. Photochemical oxidation is an advanced oxidation technology that has seen rapid development over the past decade or so. It features mild reaction conditions, strong oxidizing capacity, and a wide range of applicability, making it particularly suitable for the treatment of toxic organic compounds that are difficult to biodegrade. Currently, the most extensively studied methods are the two main categories: heterogeneous semiconductor photocatalytic oxidation and homogeneous photooxidation. The heterogeneous semiconductor photocatalytic oxidation method can generally achieve complete degradation of organic substances. For example, when using TiO2 for the photocatalytic oxidation of wastewater containing phenols at low concentrations, photolysis over 2 hours in a pH of 4 can result in a 100% removal rate of phenols. However, to be put into practical use, this method still faces many problems; issues such as low photonic quantum efficiency, reactor design, recovery and immobilization techniques for solid catalysts, as well as catalyst contamination and activation, all need to be further addressed. Semiconductor catalysts are key to the practical application of this technology; therefore, the selection of cost-effective and efficient catalysts, as well as the development of techniques for their modification and immobilization, represent important challenges for the large-scale use of this technology in wastewater treatment. Compared with semiconductor photocatalytic oxidation, homogeneous photooxidation methods that involve the use of oxidants such as O3, H2O2, and Fenton’s reagent in combination with light exhibit significantly higher oxidation capacity and photolysis rates than pure semiconductor photocatalytic oxidation. Moreover, they do not pose problems related to the recovery and fixation of catalysts, nor contamination or activation issues; hence, they represent a very simple wastewater treatment technique. Common homogeneous photooxidation systems include: UV/O3, UV/H2O2, UV/Fenton, UV/H2O2/ferrous oxalate complexes, etc. Among them, Fenton reagent is widely used in the treatment of phenol-containing wastewater. The photo-Fenton oxidation method can completely decompose phenol in a short time, but for actual wastewater with complex compositions, complete mineralization requires prolonged exposure to light as well as a large amount of oxidant. From an economic perspective, the photooxidation method is suitable for treating wastewater with low concentrations and small volumes; for wastewater with high organic matter concentrations, using only photooxidation results in high energy consumption and large amounts of oxidants, making it uneconomical. Replacing artificial light sources with sunlight can save energy and reduce costs, offering broad application prospects; however, how to improve the light efficiency of sunlight remains a focal point of research. Supercritical water oxidation uses supercritical water (Tc≥374°C, Pc≥22.1 Mpa) as a medium for oxidizing organic substances, allowing gases and organic compounds to dissolve completely in the wastewater; this eliminates the gas-liquid interface and creates a homogeneous oxidation system, **which increases the reaction rate. Many organic substances can be completely decomposed in a very short time, being oxidized into H2O, CO2, N2, and other harmless small molecules. Studies both domestically and internationally have shown that supercritical water oxidation, along with various other methods, is highly effective for the oxidative degradation of organic substances. The supercritical water oxidation method has attracted considerable attention due to its rapid reaction rate and thorough oxidation. Developed countries abroad have already built pilot-scale and industrial-scale facilities that are in operation, while research in this area in China is still in its initial stages. The supercritical water oxidation method faces the main problem of corrosion of the reaction equipment due to the reactions taking place under special high-temperature and high-pressure conditions. It requires high-quality materials for the reactors and consumes a lot of energy, which limits its industrial application to a certain extent. Developing reactor materials that can withstand high temperatures and corrosion over the long term is key to the large-scale industrial application of this method. Ultrasonic chemical oxidation is a highly efficient technology for treating organic pollutants that was developed in the late 1980s. Its principle involves using ultrasonic waves to generate cavitation bubbles at high temperatures (>5000K) as well as strongly oxidizing substances in the solution, thereby enabling the complete oxidation and degradation of hard-to-degrade organic compounds without causing any secondary pollution. However, compared with other water treatment technologies, the ultrasonic radiation degradation method still faces issues such as low treatment capacity and high costs; it is still in the exploratory stage, and there are many problems that need to be resolved before its industrial application is possible. From the perspective of environmental protection, wastewater with low phenol concentrations and no value for recycling, or wastewater that still contains residual phenol after recycling treatment, must be treated to render it harmless so that it can be discharged in compliance with standards. Given the existing limitations of current technologies for the harmless treatment of phenol-containing wastewater in practical applications, future research should focus on the following areas: enhancing research on new biological treatment processes, new technologies, and biochemical pretreatment methods. The biochemical method features a large treatment capacity, low treatment costs, and no secondary pollution, with its hardware facilities and process flows being relatively mature. It is foreseeable that for a long time to come, biochemical methods will remain the primary approach for the harmless treatment of phenol-containing wastewater. To improve biochemical treatment, it is necessary to strengthen research on new biological treatment processes, new technologies, and biochemical pretreatment techniques aimed at enhancing the efficiency of biochemical treatment. Strengthen research on the application of advanced oxidation technologies. Advanced oxidation technologies, which have seen significant development in recent years, can oxidize and degrade organic substances into CO2, H2O, and other low-molecular-weight inorganic compounds in a short period of time. They feature high removal efficiency, rapid oxidation rates, and no secondary pollution, thereby enabling harmless treatment. At the same time, they overcome the drawback of long processing times associated with biological methods, offering excellent prospects for application. However, to put it into practical use, many problems remain to be addressed, such as high equipment investment and operating costs, stringent reaction conditions, high requirements for reactor materials, and low processing capacity. Strengthen research on economical and efficient combined use technologies. Given the complexity and diversity of phenolic wastewater, it is often difficult to achieve the desired results by using just one method; therefore, a combination of several techniques needs to be considered in order to achieve efficiency and cost-effectiveness. Development trends: Incineration treatment technology is primarily used for treating high-concentration organic wastewater. Its mechanism involves oxidizing the wastewater with hot air, thereby converting organic substances into harmless small molecules such as H2O and CO2. When phenol-containing wastewater contains various other high-concentration organic pollutants in addition to phenol, resulting in a complex composition that makes the recovery of phenol difficult or uneconomical, incineration can be considered as a method for high-temperature combustion and oxidation to achieve harmless treatment. When the calorific value of the organic matter in the wastewater exceeds 4360 KJ/kg, combustion can occur automatically after ignition; only a small amount of fuel is required to preheat the incinerator, resulting in lower operating costs ； For wastewater with a low calorific value, incineration requires a large amount of fuel, resulting in high treatment costs; it is generally considered that when the calorific value of wastewater exceeds 1.05×104 KJ/Kg, using incineration as a treatment method is more economical and reasonable compared to other methods. However, due to the complex composition of actual wastewater, toxic gases may be generated during incineration, leading to secondary pollution. Incineration treatment technology and biological treatment technology: Compared with physical and chemical methods, biological approaches have the advantages of being cost-effective and efficient. More importantly, they enable harmless treatment without secondary pollution, and they can handle large volumes of waste water. They are the most widely used wastewater treatment technologies at present, and they represent the main method for the harmless treatment of phenol-containing wastewater in China. This method is effective in treating wastewater with low phenol concentrations. For wastewater with high phenol concentrations and strong toxicity, the efficiency of traditional biochemical treatment methods is low due to the inhibitory effect of toxic substances on microbial activity. To this end, scholars at home and abroad have conducted extensive research on biological treatment technologies. Improving traditional biotechnology based on the activated sludge process. The most widely used method in biological treatment is the activated sludge process. As a traditional and well-developed technique for biological wastewater treatment, it has played an important role in addressing water pollution issues, and has become the primary method for treating phenolic-containing wastewater from industries such as coking, gas production, oil refining, and wood preservation. However, this method also has drawbacks such as high operational and management requirements, low tolerance to toxins, inability to handle shock loads, low volumetric load in the aeration tank, and large sludge production; it is not effective for treating wastewater with high phenol concentrations. To improve the treatment efficiency of the conventional activated sludge process, the application of improved processes has been one of the important trends in the development of biological treatment technologies in recent years. For example, the activated sludge process with added powdered activated carbon (PACT process) can **improve the efficiency of phenol removal, reducing the concentration of phenol in the effluent to 0.01 mg/L**. In the PACT process, the adsorption of refractory organic substances and microorganisms by activated carbon prolongs the contact time of these microorganisms (equivalent to an extended sludge age), thereby increasing the opportunities for their biological degradation. As a result, the PACT process achieves a higher removal efficiency for phenol-containing wastewater compared to conventional activated sludge methods. The process of adding powdered activated carbon to the conventional Sequential Batch Reactor (SBR) process, known as PAC-SBR, takes advantage of the positive interaction between activated carbon and sludge. This not only improves the sedimentation properties of the sludge and enhances treatment efficiency, but it can also be used for the decolorization of wastewater. In addition to the improved process involving the addition of activated carbon, there is also the bio-iron method that makes use of bio-iron flocs, as well as the membrane-separated activated sludge process developed in recent years (in this process, the mixture is filtered through membranes, which traps difficult-to-degrade pollutants and certain microorganisms, allowing them to circulate within the system continuously; this increases the contact time between these substances and microorganisms, thereby enhancing the treatment efficiency). The treatment effectiveness of these improved processes is superior to that of traditional biological treatment methods.

Research Progress on Treatment Technologies for Coking Wastewater Introduction Coking wastewater is generated during the coking and gas production processes. It features large discharge volumes and complex water quality; 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 carcinogenic; therefore, the large-scale discharge of coking wastewater causes severe environmental pollution and simultaneously poses a direct threat to human health. In the early days, most coking plants used the conventional activated sludge process to treat coking wastewater. However, after entering the 1990s, as environmental awareness grew among people, our country gradually stepped up efforts to control pollution and established stricter emission standards. The \"Comprehensive Wastewater Discharge Standards\" issued in 1996 (GB8978-1996) not only included an NH3-N criterion (NH3-N＜15mg/L), but also set a stricter standard for CODcr (CODcr＜150mg/L). Coking wastewater treated by the conventional activated sludge process finds it extremely difficult to meet the requirements of discharge standards, especially regarding the CODcr and NH3-N parameters. According to a survey conducted by the Ministry of Metallurgy in 1997, over 90% of coking plants failed to meet the standards for CODcr and NH3-N after treatment. To improve the removal rates of CODcr and NH3-N, extensive research and development efforts have been carried out in recent years from the perspectives of microorganisms, process flows, and reactors, with these efforts mainly focusing on the study of biochemical treatment technologies and chemical treatment technologies. 2 Advances in biological enhancement technology: Biological enhancement technology is a method aimed at improving the treatment capacity of wastewater treatment systems, by introducing advantageous microorganisms selected from nature or highly efficient strains produced through genetic engineering techniques into such systems, in order to remove certain harmful substances or categories of them. The interactions between the inoculated microorganisms and the substrate mainly include direct interactions and co-metabolic interactions. Bioremediation technology was developed in the mid-1970s. As it enables an improvement in the scope and capacity of water treatment without the need to expand existing water treatment facilities, its application in modern wastewater treatment has gained increasing attention in recent years. Given the current situation of coking wastewater treatment in China, combining biological enhancement techniques with conventional biochemical processes is undoubtedly a practical approach. Naphthalene and pyridine are typical refractory organic compounds with high concentrations in coking wastewater. Wang Jing and colleagues isolated two naphthalene-degrading bacteria, WN1 and WN2, as well as one pyridine-degrading bacterium, WB1, from the activated sludge used in the treatment of coking wastewater through domestication and enrichment culture. The enhancement effect of adding efficient bacterial strains and microbial co-metabolism on the biological treatment of coking wastewater was studied. The results showed that the addition of co-metabolic primary substrates, Fe3+, and efficient microbial strains could all promote the degradation of refractory organic matter and increase the COD removal rate in coking wastewater; the effect was even better when these three were used together. 3 Advances in biological fluidized bed technology: In recent years, biological fluidized beds have shown great promise for the treatment of phenol-containing wastewater. A biological fluidized bed uses granular materials such as sand, coke, and activated carbon as carriers; water flows from bottom to top, keeping the carriers in a fluidized state, and a biofilm grows and adheres to the surface of these carriers. The particle size of the carrier is generally 1.0–2.0 mm. Biological fluidized beds combine the advantages of high efficiency, which is achieved through complete mixing in the activated sludge process, with the ability to withstand fluctuations in load, a feature inherent in biofilm processes. As a result, they offer excellent treatment performance, and thus have received increasing attention in recent years for treating refractory organic wastewater. There are mainly four types of biological fluidized bed technologies: air fluidized bed technology, pure oxygen fluidized bed technology, three-phase fluidized bed technology, and anaerobic-fermentative fluidized bed technology. Among them, the three-phase fluidized bed reactor is a new type of biochemical treatment device that integrates biotechnology, chemical engineering technology, and water treatment technology. Good phenol removal results have been achieved when using internal circulation biological fluidized beds, gas-lift circulation fluidized beds, activated carbon anaerobic fluidized beds, etc., to treat phenol-containing wastewater. In their study on the treatment of coking wastewater using a three-phase gas-lifted circulating fluidized bed, Cai Jianan and colleagues used untreated coking wastewater as the feedstock, employed NaH2PO4 as an external phosphorus source, and adjusted the processing load of the A1LR (an internal-circulation, side-settling three-phase gas-lifted fluidized bed reactor) by controlling the feed rate. When the COD influent load increased from 2.75 kg/（d•m3） to 13.04 kg/（d•m3）， the effluent phenol concentration ranged from 0.43–1.57 mg/L, with a removal rate of 99.5–99.8%. It maintained good relative stability even under the impact of high concentrations of phenol, cyanide, and COD, and the aeration volume was approximately 1/4–1/3 that of the activated sludge. Geng Yanlou conducted pilot-scale application research on coking wastewater using an anaerobic-anoxic-aerobic process flow, with biofilms used as the anaerobic and anoxic reactors, and an internal-circulation biological fluidized bed used as the aerobic reactor. The results show that the aforementioned process flow is feasible for the treatment of coking wastewater. When the CODcr concentration of the water entering the system is less than 1000 mg/L and the hydraulic retention time of the system is 44 hours, the CODcr concentration of the effluent is less than 250 mg/L. Paul M. Sutton and others studied the treatment of coking wastewater from the Algome steel plant in Canada using a fluidized bed reactor (FBR); the wastewater flow rate was 40 m3/h, with a phenol content of 1000 mg/L, and an equal amount of dilution water was added to control the water temperature. Two weeks later, the removal rate of phenol in the effluent from the fluidized bed reactor reached 99% ； After 5 weeks, the thiocyanate level dropped below 5 mg/L. 4 Advances in immobilized microorganism technology. Immobilized microorganism technology is a technique that has seen rapid development internationally since the late 1960s; it involves using chemical or physical methods to fix free-floating microorganisms onto carriers, thereby concentrating them highly and allowing them to remain active for repeated use. It was initially used mainly for industrial microbial fermentation production, and began to be applied in wastewater treatment in the late 1970s. At present, there is no unified classification standard for immobilized microorganism technology in China, and various methods exist; the main ones include binding immobilization, cross-linking immobilization, encapsulation immobilization, and self-immobilization. Wu Libo and others used porous ceramsite to adsorb self-immobilized mixed nitrifying bacteria for the treatment of coking wastewater, and compared the changes in bacterial activity before and after self-immobilization. The results showed that the nitrification activity of the bacteria in the attached phase and the suspended phase was similar, but when external conditions changed or toxic substances were present, the resistance of microorganisms in the attached phase was significantly stronger than that in the suspended phase. In their study on the treatment of phenol-containing wastewater using immobilized cell technology, Zhu Zhu and colleagues conducted experiments comparing the degradation of such wastewater by the same bacterial strain in an immobilized state versus a free state, demonstrating that red brick is an excellent carrier material. They also carried out kinetic analyses of the cell-mediated degradation of phenol in both states. The results showed that in both cases, the phenol degradation process by this strain followed the Monad model. In their study on the degradation of quinoline by immobilized Pseudomonas putida, Quan Xichun and colleagues isolated one strain from coking sludge through enrichment culture; this strain used quinoline as its sole carbon and nitrogen source, and was identified as Pseudomonas putida. The effects of the two methods on quinoline degradation were compared using immobilized gel beads and gauze-PVA (polyvinyl alcohol) composite carriers, and a kinetic study on the quinoline degradation by microorganisms immobilized on the gauze-PVA composite carrier was conducted. At quinoline concentrations of 50, 100, 300, and 500 mg/L, the degradation kinetic equation followed a zero-order reaction, and the degradation rate constant increased as the initial quinoline concentration increased. Sun Yan and colleagues isolated and purified a bacterium capable of degrading phenol from the phenol-containing wastewater discharged by the Beijing Coking Plant; after domestication, the bacterial strain was encapsulated using sodium alginate. The treatment results showed that, compared to free cells, the maximum reaction rates were 8.3 mg.L-1.h-1 and 83.3 mg.L-1.h-1, respectively, while the substrate saturation constants were 200 mg/L and 285.7 mg/L, respectively. It is evident that immobilized cells have great potential in the degradation of toxic substances. Huang Xia et al. used a composite carrier made of polypropylene non-woven fabric, which is stable in properties and has a porous structure, along with PVA, to encapsulate and immobilize beneficial microorganisms for the degradation of coking wastewater containing quinoline, isoquinoline, and pyridine. As a result, after 8 hours of treatment, the degradation rate of these three refractory organic compounds was over 80%. In their study on the removal of ammonia nitrogen using immobilized nitrifying bacteria, Wang Lei and colleagues used polyvinyl alcohol as an encapsulation carrier, along with an appropriate amount of powdered activated carbon, to immobilize the nitrifying sludge for the treatment of synthetic wastewater composed mainly of (NH4)2SO4 and glucose. The results of the batch experiments show that under conditions of 24–28°C, a particle packing density of 7.5%, and a residence time of 8 hours, the influent NH3-N load can be increased from 0.6 kg/(d•m3) to 3.49 kg/(d•m3); the NH3-N removal rate can reach 95.5%, while the COD removal rate remains above 80%. Zhang Tong and colleagues aimed to develop a technology for biological nitrogen removal using immobilized microorganisms, and conducted experimental studies on the separate immobilization as well as mixed immobilization of nitrifying sludge and denitrifying sludge. The results showed that immobilized mixed nitrification and denitrification sludge could achieve single-stage biological nitrogen removal, with better effects 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, respectively, compared to unfixed sludge. The results also showed that photopolymerizable resin is a good immobilization medium as well. 5 Biological nitrogen removal technology: This technology evolved from conventional biochemical treatment methods. It was first developed in Canada in the 1970s, and its practical application began in the UK in the 1980s. Subsequently, coking plants in countries such as France, Germany, and Australia also started using this technology for wastewater nitrogen removal. In our country, laboratory research on A/O (anaerobic/aerobic) treatment processes began in the late 1980s. Currently, research on biological nitrogen removal of coking wastewater focuses mainly on the A-A/O (anaerobic + anoxic/ aerobic) and SBR (sequencing batch reactor) processes. Compared with conventional biochemical treatment processes, it not only removes ammonia nitrogen pollutants from wastewater but also significantly improves indicators such as CODcr. 5.1 A-A/O Process The A-A/O process, also known as the anaerobic-anoxic-aerobic combined process, consists of three stages of biological treatment. Depending on the form in which microorganisms exist, the A-A/O process includes both the activated sludge method and the biofilm method. Min Zhang et al. studied the treatment of coking wastewater using an anaerobic-anoxic-aerobic (A-A/O) fixed-bed biofilm system. The test results show that the system can stably and effectively remove NH3-N and CODcr. When the total hydraulic retention time (HRT) of the system was 31.6 hours, the concentrations of NH3-N and CODcr in the effluent were 3.1 mg/L and 114 mg/L, respectively, with removal rates of 98.8% and 92.4%, respectively. Intermittent testing results show that anaerobic treatment differs from anoxic treatment; compared to anoxic treatment, anaerobic treatment achieves a lower removal rate for phenols, but a higher removal rate for complex macromolecular organic compounds, and its biodegradation capacity is greater than that of anoxic treatment. To overcome the disadvantages of easy loss of suspended sludge, poor resistance to fluctuations in water quality and volume, and unstable operation, Wu Libo and others took coking wastewater as the research subject and employed an anaerobic-anoxic-aerobic process (A-A/O). spherical fillers were added to the aerobic stage to create a composite reactor for the treatment of coking wastewater. The test results show that in the aerobic combined reactor, the sludge concentration in the attached phase is higher than that in the suspended phase. The attached-phase sludge exhibits greater degradation capacity and resistance to inhibition for three representative pollutants in coking wastewater—phenol, quinoline, and ammonia nitrogen—compared to the suspended-phase sludge. Li Yongmei used the anaerobic acidification-anoxic-aerobic (A-A/O) biofilm process to treat the wastewater from Shanghai Coking Plant. The test results show that when the influent COD is 600–1000 mg/L and the ammonia nitrogen level is 200–280 mg/L, to achieve both good removal of organic substances and effective nitrogen removal, the HRT of the system should be at least 34.5 hours, the mixed liquor recirculation ratio should be 4.0–5.0, the pH value in the aerobic stage should be maintained between 7.8–8.0, and the residual alkalinity in the effluent should be 100–200 mg/L. Methanol must be added as an external carbon source in the hypoxic section, with a ratio of methanol to nitrate nitrogen of 2.58:1 being appropriate. 5.2 SBR Process SBR is a new activated sludge process developed in recent years. It carries out the anoxic, anaerobic, and aerobic processes in sequence within the same reactor, through programmed control of five stages: water filling, aeration reaction, sedimentation, water discharge, and sludge discharge, thereby achieving the biochemical treatment of wastewater. Practice has shown that when the SBR process is used to treat high-concentration and hard-to-degrade organic substances, as well as to remove nitrogen, phosphorus, and sulfur biologically, it can achieve significantly better water quality in the effluent compared to conventional activated sludge processes. Hanqing Yu et al. used the SBR process to treat coking wastewater. The results show that using a period of anoxic treatment before and after the aeration stage yields better nitrogen removal effects than other methods (pre-nitrification denitrification and post-nitrification denitrification). 4 hours of anoxic treatment allows some of the substrates in the influent to be stored within the organisms, thereby enabling denitrification during the second anoxic phase. Under the above conditions, the removal rates of NH3-N and CODcr were 82.5% and 65.2%, respectively. Some biodegradable organic substances in the influent water, such as phenols and cresols, are used as carbon sources in the denitrification stage. 16 hours of aeration significantly reduced the concentrations of cresol, 3,4-dimethylcresol, and 2-quinolineethanol, but the removal of quinoline, isoquinoline, indole, and methylquinoline was not significant. Min Woo Lee et al. investigated the feasibility of completely removing NH3-N from coking wastewater using the SBR process, with sodium acetate as an external carbon source. The results show that the addition rate of the external carbon source can significantly affect the efficiency of denitrification, with the optimal rate determined by the ratio of COD to NOx-N during the denitrification stage. In biological nitrogen removal systems, the total removal rate of soluble pollutants in wastewater is greater than 95%. Given that traditional A/O or A-A/O processes find it difficult to reduce the COD of coking wastewater to below 100 mg/L, Li Chunjie and colleagues introduced PVDF (polyvinylidene fluoride) hollow fiber membranes into SBR reactors, thereby using an integrated membrane sequencing batch biological reactor (SMSBR) to enhance the treatment of coking wastewater. Preliminary research results show that under conditions of an HRT of 32.7 hours, an SRT of 600 days, and an average COD volumetric load of 0.45 kg/(d•m3), the COD level in the membrane effluent can be maintained below 100 mg/L (with an average value of 86.4 mg/L). The COD trapped by the membrane is further degraded in subsequent reactions, with no significant accumulation occurring ； Under the conditions of maintaining temperature and alkalinity, the NH3-N concentration in the effluent is below 1 mg/L. During this process, the membrane fouling rate is relatively high. 6 Advances in Chemical Technology 6.1 Catalytic Wet Oxidation Technology Catalytic wet oxidation technology involves the use of air, under high temperature and pressure conditions and with the help of catalysts, to oxidize ammonia nitrogen and organic pollutants in wastewater, ultimately converting them into harmless substances such as N2 and CO2 for emission. Research on this technology began in the 1970s. Coking and petrochemical industries, especially those involving high-concentration wastewater containing toxic pollutants such as pesticides, dyes, rubber, synthetic fibers, as well as flammable, explosive, and biodegradable substances, are suitable for catalytic wet oxidation treatment. Our country also began research in this field quite early on. From 1987 to 1992, Anshan Coking Institute collaborated with the Dalian Institute of Physics and Chemistry of the Chinese Academy of Sciences to successfully develop a two-component, highly active catalyst that exhibits excellent performance in treating high-concentration wastewater containing complete nitrogen compounds and organic substances resulting from coking processes. The disadvantage of this technology is the high cost of the catalyst. In recent years, there have been few research reports at home and abroad on the use of catalytic wet oxidation technology for treating coking wastewater. 6.2 Electrochemical oxidation technology Li-Chong Chiang and others used PbO2/Ti as electrodes to study the treatment of coking wastewater by electrochemical oxidation. The results showed that after 2 hours of electrolysis, the COD in the wastewater decreased from 2143 mg/L to 226 mg/L, with a removal rate of 89.5%. In addition, approximately 760 mg/L of NH3-N in the wastewater is also removed simultaneously. The study found that the electrode material, oxide concentration, current density, and pH value have a significant impact on the COD removal rate and the efficiency of current during electrochemical oxidation. Furthermore, the chlorides/high-chloride compounds generated during the electrolysis process can cause indirect oxidation, which plays an important role in removing pollutants from coking wastewater. 6.3 Using flue gas to treat residual ammonia water from coking or all coking wastewater: To completely address the pollution problem caused by coking wastewater, Yin Guangjin and others adopted a treatment technique that is entirely different from biochemical methods, namely using flue gas to treat residual ammonia water from coking or all coking wastewater. This technology has been granted an invention patent and has been successfully applied in the treatment of residual ammonia water from coking processes at Jiangsu Huaiyang Iron and Steel Group. In the process of treating coking residual ammonia water in boiler flue gas, the wastewater comes into contact with the flue gas in a spray tower, where physical and chemical reactions occur. All of the wastewater is vaporized, and SO2 in the flue gas, NH3 in the wastewater, and O2 in the tower undergo a chemical reaction to form (NH4)2SO4. The organic pollutants adsorbed in the smoke and dust are decomposed into non-toxic substances within high-temperature roasting furnaces or boiler chambers, thereby achieving zero discharge of wastewater and avoiding any pollution impact on the atmospheric environment. This process utilizes waste to treat waste; it not only achieves good treatment results but also offers the advantages of low investment and low operating costs. 7 Conclusion In recent years, as emission standards have become increasingly stringent, scholars around the world have carried out some new and valuable explorations in the field of treatment technologies for coking wastewater. Bioremediation technology can enhance the scope and capacity of water treatment by building on existing wastewater treatment facilities, and is quite suitable for the current situation of wastewater treatment in China’s coking industry ； Immobilized microorganism technology, biological nitrogen removal technology, and biological fluidized bed technology improve traditional biochemical treatment methods from the aspects of microorganisms, process flows, and reactors, and hold great potential for application in the treatment of coking wastewater ； Chemical technology offers a new approach for the treatment of coking wastewater. Compared with biochemical technology, this method features simpler processes, faster reaction rates, and higher purification efficiency; however, its drawback is the higher investment and treatment costs.

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