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The petrochemical industry is an industrial sector that generates large amounts of waste, is prone to causing pollution, and poses a threat to the environment. The characteristics of petrochemical production determine the prevalence and complexity of pollution. Therefore, as the petrochemical industry develops at a faster pace, it is essential to pay close attention to pollution control, which is of great significance for the sustainable development of this industry. 1 Characteristics of petrochemical wastewater 1.1 Difficulty in wastewater treatment The main pollutants in petrochemical wastewater can generally be categorized as hydrocarbons, hydrocarbon compounds, as well as soluble organic and inorganic components. The soluble inorganic components include mainly hydrogen sulfide, ammonia compounds, and trace heavy metals ； The soluble organic components can be biodegraded in most cases; however, there are a few that are difficult or unable to be biodegraded, such as crude oil, gasoline, and propylene. As the exploitation period of oil fields extends, especially in the middle and later stages of development, although the water content in crude oil increases, the period during which extraction can be carried out without water becomes shorter. At present, the overall water content in crude oil from most oil fields in China has reached 80%, with some even reaching 90%. The amount of oil extraction wastewater generated each year is approximately 410 million tons, making it a major source of oily wastewater. The hydrocarbons in oily wastewater mainly consist of floating oil, dispersed oil, emulsified oil, colloidal dissolved substances, and suspended solids. The floating oil in oily wastewater floats on the water as a continuous phase, and such pollutants can generally be removed by mechanical or physical methods. The solubility of oils in water is very low, usually only a few milligrams per liter. The method for removing dissolved oils from water must be determined based on their chemical properties. 1.2 High wastewater discharge volume: The production processes in the petrochemical industry are relatively complex, resulting in large variations in the amount of wastewater generated. In oil refining, for example, depending on the degree of processing, the wastewater volume produced per 1,000 tons of crude oil varies significantly, ranging from 0.69 to 3.99 m3, with an average value of 2.86 m3' ； The wastewater discharge volume for producing each ton of petrochemical products is 35.81–168.86 m3, with an average of 117 m3. For each ton of petrofiber products, the wastewater discharge volume is 106.87–230.67 m3, with an average of 161.8 m3. The wastewater discharge volume for producing each ton of chemical fertilizers is 2.72–12.2 m3, with an average of 4.25 m3; the average wastewater discharge volume for producing each ton of synthetic rubber is 3.31 m3. During periods of abnormal production, or when there are shutdowns or maintenance activities, the wastewater discharge volume varies even more significantly. 1.3 The pollutant components in wastewater are complex. The wastewater generated in the processes of oil refining, petrochemicals, petroleum-based fibers, fertilizer production, and synthetic rubber manufacturing contains, in addition to oils, sulfur, phenols, COD, ammonia nitrogen, SS, acids, bases, salts, etc., various organic substances and organic chemical products such as alcohols, ethers, ketones, aldehydes, hydrocarbons, organic acids, oils, high-molecular polymers (polyesters, fibers, plastics, rubbers), and inorganic substances. During abnormal production, start-up and shutdown periods, as well as maintenance times, the pollutant levels in the wastewater discharged vary more significantly, often resulting in shock loads. 2 Principles for the treatment of petrochemical wastewater 2.1 Control the production process to minimize water pollution Enhance environmental protection awareness in the production process, continuously improve technologies and equipment, and use production processes, equipment, and raw materials that cause little or no pollution, in order to reduce waste discharge and wastewater output to the greatest extent possible. 2.1.1 Controlling the production process: In the petroleum processing process, vacuum distillation of the dry type is used instead of wet vacuum distillation, and reboilers are employed in place of steam stripping. Catalytic hydrogenation is used for product bonding instead of acid-base washing. 2.1.2 Selection of appropriate production methods: In the petrochemical production process, the low-alkali alcoholysis method is used instead of the high-alkali alcoholysis method to produce polyvinyl alcohol, and the pyrolysis process is employed instead of the dehydrogenation process to produce alkylbenzenes. In the production of petroleum-based fibers, the direct esterification method is used instead of the transesterification method to produce polyester melts and chips, while dry spinning is employed instead of wet spinning for the production of acrylonitrile. 2.2 Saving water, increasing the reuse rate of water, and reducing wastewater discharge: Depending on the different requirements regarding water temperature and quality in the processes of oil refining, chemical manufacturing, fiber production, and fertilizer production, methods such as using the same water in multiple stages in sequence, recycling water, and reusing wastewater after treatment are adopted to reduce the amount of wastewater discharged during production. 2.2.1 Multiple uses of water: The water used once in the boiler is first utilized for condensation and cooling in the process, then heated before being sent to chemical water treatment for desalination; thereafter it is sent to the deaerator for deoxygenation before being fed back into the boiler. The cooling water from the butadiene distillation tower and dehydrator is used in series before being sent to the circulating water plant as make-up water. 2.2.2 Recycle Utilization: For the condensation and cooling steps in the process, air cooling or wet air cooling should be preferred over water cooling. For processes that require water cooling, circulating water is used for cooling. Improve water quality, strengthen the stabilization treatment of water quality, and increase the concentration ratio of circulating water, thereby reducing the amount of water needed to replenish the circulating water and minimizing the volume of wastewater discharged. 2.2.3 Wastewater reuse – Seek alternative sources and reduce consumption by utilizing reclaimed water systems for wastewater reuse. The purified water obtained by stripping H2S, ammonia, and cyanide from the sulfur- and ammonia-containing condensate generated during the refining process can be reused as feedwater for electrodesalination. Cold coking water and cut coking water are recycled in a closed loop after oil separation, sedimentation, and filtration. The wastewater from the washing tank is recycled \"in situ\" after oil separation, flotation, and filtration. The wastewater treated at the secondary level is used as backwash water for the wastewater treatment filter beds, as well as as make-up water for gas tanks and flare water seal tanks. 2.3 Strengthen hierarchical control, and carry out local pretreatment as well as comprehensive recycling of pollution sources. The pollutants contained in the wastewater generated by petrochemical processes are mostly materials that are lost during the production process, as well as useful substances. Therefore, to manage wastewater, it is necessary to strengthen control over pollution sources, implement local pretreatment of wastewater and its comprehensive recycling, recover useful materials from the wastewater, reduce consumption, and turn what is harmful into something beneficial. This is an effective way to remove pollutants from wastewater and reduce environmental pollution. 3 Technologies and Methods for Treating Petrochemical Wastewater 3.1 Adsorption The adsorption method makes use of the porous structure, large specific surface area, and hydrophobic and oleophilic properties of adsorbents to enable oil to be adsorbed on their surfaces or within their pores through physical or chemical processes, thereby achieving oil removal. Common adsorbents are made from materials such as coal ash, slag, fruit shells, sawdust, and clay; they undergo carbonization, activation, or organic modification to increase the pores, raise the specific surface area, and enhance surface oleophilicity. Generally, adsorbents are divided into two types: powdered and granular. The powdered type is added directly to water, while the granular type is used in the form of adsorption columns. 3.2 Membrane Technology In recent decades, membrane separation technology has developed rapidly. Abroad, membrane technology has been widely applied in research and industrial trials for the removal of emulsified oil and dissolved oil from oily wastewater, as well as for desalination. The characteristics of microfiltration (MF) and ultrafiltration (UF) technologies for treating oily wastewater are as follows: no chemicals are used, it is a pure physical separation process that does not generate sludge; it has strong adaptability to changes in the oil concentration in the raw water; pressure is required to circulate the wastewater, the inlet water must be carefully treated, and the membranes need to be disinfected and cleaned regularly. The simple mechanism for oil removal is that emulsified oil is prevented from passing through the membrane due to the larger size of its oil droplets compared to the membrane pores, while dissolved oil is prevented from passing through based on the interactions between the molecules of the membrane and the solute. The stronger the hydrophilicity of the membrane, the greater its ability to prevent free oil from passing through, resulting in a higher water flux. The state of existence of oil in oily wastewater is the primary factor in selecting a membrane; if the oil in the water is emulsified into stable emulsified oil and dissolved oil due to the presence of surfactants, making it difficult for the oil droplets to stick together, then hydrophilic or lipophilic ultrafiltration membranes must be used for separation. For this purpose, the pore size of the ultrafiltration membrane must be large enough