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Abstract: With the development of industry today, the issue of treating coking wastewater generated by industrial activities is attracting increasing attention. Especially in our country, China is now the world’s largest producer of coke. The treatment of coking wastewater is even more crucial. If coking wastewater is discharged in excess of the allowed levels, it will cause significant harm to the environment. Below, an analysis of the current status of coking wastewater treatment will be presented, along with a review of physical and chemical methods, biochemical methods for coking wastewater treatment, as well as foreign treatment technologies. 1 Introduction At present, the conventional activated sludge process is widely used for treating coking wastewater; it can effectively remove substances such as hydrogen sulfide and cyanide from the wastewater, but its efficiency in removing COD and NH3-N is extremely poor, to the point where it is unable to remove them at all. Production experience shows that the main challenges in treating coking wastewater lie in removing organic substances and NH3-N. Due to the toxic effects and inhibitory impact of ammonia nitrogen and organic compounds such as polycyclic aromatic hydrocarbons on microorganisms, there are deficiencies in the technologies used for treating coking wastewater, which results in high treatment costs. The main mature methods for treating coking wastewater include physical methods, chemical methods, biochemical methods, and physicochemical methods ； At present, most coking plants primarily use biochemical and physicochemical methods to treat coking wastewater. 2 Pretreatment technologies for coking wastewater: Some of the organic substances in coking wastewater are not easily biodegradable, so appropriate pretreatment technologies are required. The commonly used pretreatment method is anaerobic acidification. It is a process that lies between anaerobic and aerobic conditions; its mechanism of action involves the use of anaerobic microorganisms to carry out hydrolysis and acidification, thereby altering the chemical structure of hard-to-degrade organic substances and converting them into substances that are easier to degrade. Pre-treatment of coking wastewater through anaerobic acidification can improve the aerobic biodegradability of recalcitrant organic compounds, thereby creating favorable conditions for subsequent aerobic biological treatment. 3 Secondary treatment technologies: 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 is still very difficult for parameters such as **, 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 extensive research in recent years, developing many relatively effective treatment technologies for coking wastewater. 3.1 Physicochemical treatment methods 3.1.1 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. Shanxi Coking Group Co., Ltd. uses boiler fly ash to treat coking wastewater from biochemical processes. After being treated with fly ash adsorption, the average removal rate of pollutants in biochemical effluent is 54.7%. The treated effluent meets the **first-class standards for new coking plants** in terms of all pollutant indicators except ammonia nitrogen. These results are comparable to those achieved by the A/O method; however, the investment cost is only half that of the A/O method. 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 coke residue 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 mI/min, a pH of 2–2.5, and a temperature of 25°C. 3.1.2 Utilization of flue gas for treating 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 gas reacts with SO2 in the flue gas to form ammonium sulfate. This patented technology has been successfully applied in the treatment of residual ammonia water from coking processes at Jiangsu Huaiyin Iron and Steel Group. Monitoring results show that all the residual ammonia water from coking has been treated, achieving zero discharge of wastewater; at the same time, compliant emissions of flue gas have been ensured. The main pollutants discharged into the atmosphere, such as ammonia, phenols, and **, account for 1.0–4.7% 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 required by the flue gas, which limits the applicability of this method to a certain extent. 3.2 Biochemical methods: Biochemical methods make use of the oxidation, decomposition, and adsorption capabilities of microorganisms to treat organic pollutants in wastewater. This is one of the most widely used and effective methods in wastewater treatment. In recent years, efforts have been made from aspects such as microorganisms, reactors, and process flows to develop technologies such as the activated sludge process, biofilm process, biological fluidized bed, immobilized biological treatment techniques, and biological nitrogen removal technology. The development of these technologies has enabled the biodegradation of most organic substances, resulting in a significant improvement in the quality of the treated water. 3.2.1 Activated Sludge Process The activated sludge process involves bringing biological flocs and activated sludge into full contact with the organic matter in wastewater; the soluble organic matter is absorbed and adsorbed by the cells, and is ultimately oxidized to end products (mainly CO2) ； Insoluble organic matter is first converted into soluble organic matter, and then metabolized and utilized. However, when this technology is used alone, it is difficult to meet the standards for indicators such as COD, BOD, and NH3-N in the effluent; in particular, it has almost no degradation effect on NH3-N. 3.3.2 Biofilm Process The membrane bioreactor (MBR) shares the same biochemical mechanism as the conventional activated sludge process in removing organic matter and NH3-N; the difference is that the conventional activated sludge process carries out sludge-water separation in a sedimentation tank. The MBR unit produces water through membrane filtration, while retaining the sludge in the reaction tank. Using the MBR process to treat coking wastewater, under the same biochemical tank volume conditions, its COD removal efficiency can be increased by 30% compared to traditional processes, while the NH3-N removal efficiency can be increased by 50%. The SS removal rate can reach 100%. The MBR method has the advantages of being cost-effective, simple, efficient, and having a large treatment capacity. Most importantly, it enables harmless treatment without causing secondary pollution, and it has been widely applied in coking plants across various locations. The successful application of the MBR process in the treatment of coking wastewater is of great significance for steel enterprises and coal chemical enterprises in saving water resources and reducing wastewater pollutant emissions. 3.3.3 Biological fluidized bed technology The biological fluidized bed technology is a treatment method that combines the conventional activated sludge process with the biofilm process; its development began in the early 1970s. Its carrier is in a fluidized state within the fluidized bed, enabling full contact among the solid (biofilm), liquid (wastewater), and gas (air) phases, as well as intense collisions between the particles. The surface of the biofilm is constantly being renewed, and microorganisms remain in a phase of vigorous growth. Biological fluidized bed technology has attracted widespread attention from researchers due to its advantages such as high treatment efficiency, high volume load, fast mass transfer rate, and wide range of applications. 3.3.4 Biological nitrogen removal technology: Biological nitrogen removal technology was developed on the basis of conventional biochemical treatment methods. It was first introduced in Canada in the 1970s, and the UK was the first to put it into practical use in the 1980s. Since the conventional activated sludge process finds it difficult to remove NH3-N and COD from wastewater to meet **discharge standards, biological nitrogen removal technologies such as A/O, M/O, A/02, and SBR processes were developed one after another. Among them, the A/02 process is an extension of the A/O process, and both belong to biological nitrogen removal processes based on the A/O framework. Wang Xianguo conducted research on the treatment of coking wastewater using the A/O denitrification technology. The results show. The A/O process can both remove nitrogen and degrade a large amount of organic matter in wastewater, making it an ideal wastewater treatment technology; the quality of the treated water can generally meet **secondary discharge standards. The A/O process achieves a significantly higher pollutant removal rate compared to the activated sludge process, but it requires a longer hydraulic retention time, and its effectiveness in removing recalcitrant organic compounds from coking wastewater is not very good. The A/O process is a biological treatment technology developed in the 1990s. This technology adds an anaerobic pretreatment stage to the A/O process; through the repeated alternation between aerobic and anaerobic conditions, certain organic substances such as recalcitrant polycyclic aromatic hydrocarbons are degraded, resulting in a significant increase in the removal rates of phenols, cyanides, and COD, **thus enhancing the biodegradability of the wastewater. Studies by I. Vdazquez et al. show that for COD of 922. 1,980 mg/L for the former, 133,293 mg/L for volatile phenols, and 176 for SCN-. 362 mg/L, and NH3-N is 123. For coking wastewater at a concentration of 296 mg/L, treatment using the A2/0 process resulted in removal rates of 90.7% for COD and 99.9% for NH3-N. The A2/O biological denitrification wastewater treatment technology achieves good results in treating COD and NH3-N in coking wastewater, yet the effluent after treatment still finds it difficult to meet the required standards consistently. The A/02 process is mainly used to remove COD and NH3-N from wastewater. The main process of Xingang’s wastewater treatment plant adopts the A/02 process. Its biological treatment section consists of the A/02 tank and a secondary sedimentation tank, with perforated aerators being used for oxygenation in the O tank. Practice has shown that, for the same total reaction time, A/02 achieves a higher removal rate of COD and NH3-N compared to A2/O; the COD and NH3-N levels in the effluent remain within acceptable limits. Moreover, A/02 requires no large amount of biological filler or water distribution devices. Shanghai Baosteel Coking Plant replaced its original MO biological nitrogen removal process with the A/02 process. Production operation experience shows that the improved process achieves better treatment results than the A/O process, with reduced operating costs. Overall, the biochemical method has advantages such as the ability to treat large volumes of wastewater and a wide range of wastewater types. However, it requires large-scale treatment facilities, long retention times, high investment costs, and strict requirements regarding the quality of the wastewater. 3.3.5 Foreign biochemical treatment technologies Scholars both at home and abroad have conducted extensive research on the biochemical treatment of coking wastewater. These include the SBR (sequencing batch reactor) process, MBR (membrane bioreactor) process, A/O (anaerobic-aerobic) process, immobilized high-efficiency microbial treatment process (3T–AF/BAF process), and bio-augmentation technology, among others. 3.3.5.1 SBR process: Maran et al. used the SBR process to treat coking wastewater. After pretreatment via stripping, 96% of the ammonia nitrogen was removed (HRT=66 h). In the SBR reactor, with an HRT of 115 h, the removal rates for COD, thiocyanate, and phenol were 85%, 98%, and 99%, respectively. The final concentrations were ρ(phenol)=118 mg/L, ρ(SCN–)=514 mg/L, and ρ(COD)=206 mg/L. For treating coking wastewater, the long hydraulic retention time required by the SBR process results in large-scale equipment, and the highly toxic substances present in coking wastewater can also affect the stability of operation. 3.3.5.1 A 2/O process: Li et al. compared the treatment efficiency of the A 2/O and A/O processes for coking wastewater; under conditions of roughly similar hydraulic retention time (HRT), these two systems achieved almost identical treatment effects on COD and NH3-N. Since A/0 adds a hydrolysis-acidification stage, it has a better treatment effect on organic nitrogen and total nitrogen than A/O. Qiu Xianhua et al. [15] found that, under optimal conditions, the A/O fixed-bed biofilm system achieved fairly satisfactory results in carbon removal, nitrification, and denitrification. 4 Conclusions (1) The biochemical method has advantages such as the ability to treat large volumes of wastewater, a wide range of applicable waste streams, low treatment costs, and no secondary pollution, making it the primary method for treating coking wastewater ； Physical-chemical methods serve as a useful complement to biochemical methods. Utilizing the synergistic effects of various methods to treat coking wastewater allows for the utilization of their respective advantages, thereby helping to further improve treatment efficiency. Therefore, the organic combination and integration of various methods represent the development trend in coking wastewater treatment technologies. (2) Through continuous research and practice, many methods have been developed for treating coking wastewater, and good treatment results have been achieved. However, there are also some drawbacks; for example, the COD level of the treated wastewater rarely manages to meet the **first-class discharge standards, and the quality parameters of the effluent are unstable. Therefore, as environmental regulations become increasingly stringent, there is still much work to be done to ensure stable and high-standard discharge of coking wastewater, and this represents a challenge that needs to be addressed in the future. [References] Shan Mingjun, Lü Yanli, Cong Lei, Treatment Technologies for Coking Wastewater. Beijing: Chemical Industry Press, pp. 30–31. Mo Tianlin, Xie Guoliang, A Preliminary Study on the Acidity of Precipitation in Nanjing. Acta Meteorologica Sinica, 1981(4): 10–21. Zhang Changming, Research on Purification and Reuse Technologies for Coking Wastewater. 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