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New Advances in Petrochemical Wastewater Treatment Technologies. In recent years, rapid progress has been made both domestically and internationally in areas such as activated sludge technology for wastewater treatment, technologies for the harmless treatment of refractory wastewater, membrane bioreactor (MBR) technologies for wastewater treatment, and wastewater reuse technologies. Many new technologies have already been adopted and applied in petrochemical enterprises. This article provides a review of this topic. 1 Physicochemical treatment technologies 1.1 High-efficiency flocculation and flotation technology Dalian Light Industry Institute and Dalian Minsheng Environmental Protection Technology Co., Ltd. have developed a new series of environmentally friendly flocculants based on starch and carboxymethyl starch, using corn starch as the main raw material and combining it with a small amount of acrylate. These flocculants overcome the disadvantages of traditional polymer flocculants, such as high costs and toxicity, enabling efficient, economical, and pollution-free wastewater treatment. It is said that this new type of flocculant can be used alone for wastewater treatment, or in combination with other inorganic coagulants. It requires a small amount, yields good results, and is easy to use. Pilot-scale production on a thousand-ton scale has already been successfully carried out, and the product has been successfully applied in industries such as the Daqing Oil Field, Kunming’s Dianchi Lake, as well as the petrochemical, papermaking, printing and dyeing, and coal washing sectors. According to the application report from Dalian Oil Production Plant No. 6, treating oily wastewater with this product for 3S enables complete separation of oil and water, with an oil removal rate of over 90%; the resulting water is transparent, and it is also possible to remove heavy metal ions from the water, meeting the requirements for reinjection water. Harbin Institute of Technology Environmental Protection Technology Co., Ltd. utilizes agricultural waste in the form of straw to produce composite biological coagulants on a large scale through biotechnology, thereby converting industrial and domestic wastewater into clean water using low-cost biological methods without causing any secondary pollution. Through practical applications in the water sources of the Songhua River, the water used by the Daqing Central Water Intake Plant, and domestic wastewater, not only has the reliability of this technology been proven, but benefit analyses also show that the widespread adoption of this project brings significant economic, environmental, and social benefits. This project uses agricultural waste such as straw fibers and wastewater from biohydrogen production as raw materials for the preparation of biological flocculants, offering a scientific and comprehensive process for the industrial production of these flocculants. The purification capacity for domestic wastewater, highly acidic wastewater, ink wastewater, traditional Chinese medicine wastewater, and slurry wastewater. Due to the low cost of raw materials, the price of this biological flocculant is not only much lower than that of existing biological flocculants, but it is even slightly lower than that of some chemical flocculants. A method for treating wastewater generated in the production of acrylonitrile-butadiene copolymer (ABS wastewater), developed by Daqing Petrochemical Company of China National Petroleum Corporation, has been granted a **patent. This patented technology involves adjusting the pH of the wastewater from ABS production units to 6–8 using inorganic acids under mechanical stirring, adding basic polyaluminum chloride, and mixing thoroughly under mechanical stirring. Polyacrylamide is then added and mixed evenly. The ABS wastewater is subsequently left to settle; the supernatant is sent to subsequent wastewater treatment processes, while the sediment undergoes solid-liquid separation. The separated liquid is returned to the pH adjustment stage for further recycling, and the solid material is recovered. By utilizing this patented technology, the biodegradability of wastewater can be improved, the organic load on subsequent wastewater treatment systems can be reduced, the occurrence of clogs can be minimized, and the proper operation of wastewater treatment processes is ensured. At present, the vast majority of oil fields in our country are in the middle to late stages of oil extraction; the water content in the crude oil extracted from underground is increasing gradually, and the volume of oily wastewater that needs to be treated is also rising year by year. In particular, the high-oil-content wastewater generated in tertiary oil recovery not only causes abnormal operation of surface facilities, formation blockage, and environmental pollution, but also leads to a large amount of crude oil being reinjected underground, resulting in significant waste. Therefore, the use of liquid treatment technologies has actually become a bottleneck restricting the widespread adoption of tertiary oil recovery technologies in our country. The Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, has carried out research and development on the preparation of organic polymer flocculants through dispersion polymerization in an aqueous medium. Using weathered coal, which is abundant, inexpensive, and has a low calorific value, as the main raw material, this institute has developed new wastewater treatment agents for oil fields through aqueous dispersion polymerization technology. Currently, it is being developed in collaboration with Jilin Shenda Construction Company; production of a 300t/a weathered coal-grafted wastewater treatment agent has been achieved, and its practical application has been tested at the Daqing Oil Field. This new type of low-cost and high-efficiency oilfield wastewater treatment agent, which uses natural, low-value products as a partial substitute for organic raw materials, breaks through the limitations that have hindered the widespread application of third-generation oil recovery technologies in China, thus laying a foundation for their use. This research achieved significant technological innovations; in particular, the technique of using weathered coal for in-situ polymerization to produce water treatment agents not only avoids the use of strong acids and bases in the environment but also opens up a new approach. It represents a pioneering achievement in the fields of weathered coal utilization and water treatment agent synthesis. Secondly, the introduction of humic oil, which is abundant in weathered coal, addresses issues such as high energy consumption and large equipment investment in treatment. At the same time, this technology features a simple production process, environmental friendliness, and low production costs, giving it very broad prospects for practical application. As China’s kerosene processing capacity continues to increase, the scale of wastewater treatment also needs to be expanded accordingly. The goals for wastewater reuse require higher standards for the water quality after treatment. Air flotation technology utilizes microbubbles to capture and remove finely dispersed oils, emulsified oils, gums, and suspended solids from water. It not only ensures the quality of water for biochemical treatment but is also commonly used in post-biochemical treatment; it is an essential component in the wastewater treatment process of kerosene plants. Among them, impeller air flotation has developed more rapidly due to its advantages such as simple equipment structure, low investment costs, small space requirement, low energy consumption, and easy operation. In the impeller air flotation oil removal technology, the self-priming air-liquid mixing impeller is one of the key components. The Fushun Petrochemical Research Institute of Sinopec addressed the issues existing in current self-priming gas-liquid mixing impellers, and developed a technology capable of effectively removing oil and COD from oily wastewater – the FYHG-DO type impeller air flotation oil removal technology. The impeller of this technology achieves significantly higher vacuum levels and suction capacities compared to the control impeller, effectively resolving the issue of balancing suction volume and liquid intake volume, and thus ensuring good gas-liquid mixing. Actual test results show that after treatment with the impeller air flotation oil removal technology, the oil removal rate in the oily wastewater is 67%, while the COD removal rate is 31%. Experts recommend conducting industrial application tests as soon as possible. 1.2 Magnetic powder purification technology: A new method for purifying wastewater using magnetic powder, which makes the purification process more efficient and reduces the costs associated with treatment. In the widely used activated sludge process, organic pollutants in wastewater are consumed through the growth and metabolism of microorganisms. As the bacteria degrade the pollutants, they also aggregate into spherical flocs and settle to the bottom of the treatment tank. This process is quite effective for purifying wastewater, but it has its drawbacks; sometimes the fine bacteria in the sludge form clusters, which hinders the settling of the sludge. In severe cases, this can cause the treatment facilities to stop operating. Another important issue with the activated sludge method is that bacteria multiply as pollutants are consumed, resulting in an excessive amount of sludge that requires significant costs to clean and treat. Yasuzo Saka, a professor of applied chemistry at Utsunomiya University in Japan, devised an improved method to solve the aforementioned problem: by adding a small amount of magnetite (Fe3O4) powder to the activated sludge, the magnetized sludge can be scraped off the drum and recycled back to the treatment tank for further use. The research team led by Saka precisely optimized the microbial concentration under the treatment conditions to prevent the formation of excess sludge. This process has been effectively used to treat urban wastewater, wastewater from the information technology industry, as well as wastewater containing phosphorus and nitrogen. For example, from the end of 2003 to August 2005, urban wastewater was treated using a medium-scale unit based on the 16 m3 magnetic activated sludge process; during a 500-day trial, this process was able to effectively remove organic substances without generating excessive sludge. 1.3 Wet oxidation technology: To carry out harmless treatment of organic wastewater that is difficult to treat, the Sino-Japanese joint venture Yunnan Gaoke Environmental Protection Engineering Company adopted the catalytic wet oxidation process technology developed by Osaka Gas Company in Japan. It managed to localize the entire range of equipment, design, and installation processes, and established a catalyst production line with a capacity of 30 t/d. The cost of this system is only 50%-60% of that of imported equipment, and it has been exported to Japan. This technology uses oxidation catalysts to treat hard-to-degrade waste streams, with costs ranging only from 50% to 60% of those of imported equipment, and it has been exported to Japan. This technology uses oxidation catalysts to completely and harmlessly decompose refractory organic wastewater; the quality of the treated water meets the **discharge standards**, and the heat generated during oxidation is recovered and utilized as a heat source for the process or to produce steam. Compared with traditional biochemical treatment and incineration methods, this technology features simpler equipment, smaller floor space, and the ability for automated operation. It does not produce exhaust gases such as sulfur oxides, nitrogen oxides, or dioxins, nor does it generate sludge; it is therefore a highly efficient and environmentally friendly process technology. The values are below mg/l; the phenol concentration drops from 10 g/l to below 2 mg/l, and the COD drops from 150 g/l to below 500 mg/l, meeting the water quality standards for the inlet water of kerosene wastewater treatment plants. This solution has been applied in more than 10 petrochemical enterprises in cities such as Shanghai, Daqing, and Qingdao. China’s refineries and chemical plants that use petroleum distillates as raw materials mostly employ alkali refining processes, which generate large amounts of alkaline wastewater containing high levels of pollutants. Pollutants such as COD, sulfides, and phenols in this wastewater are the main sources of unpleasant odors. The Fushun Research Institute of Petrochemicals of Sinopec and its Shanghai Gaoqiao branch have developed industrial application technologies for the treatment of alkali sludge and wastewater from refineries. By using a combined mild wet oxidation and intermittent activated sludge process (SBR), they have successfully created five proprietary equipment and process technologies, including an internal-circulation mixed oxidation reactor, systems for separating the gas-liquid mixture after deodorization, cooling units, and exhaust gas recirculation cooling towers. They have also obtained two patents related to the treatment of waste alkaline solutions. Industrial test results show that the application of this technology can reduce the mass concentration of sulfides in waste alkaline solutions from 8 g/l to 0.5 g/l. The wet oxidation treatment unit for alkaline slag wastewater, built by Sinopec Luoyang Petrochemical Company, has been operating continuously at Sinopec Guangzhou Petrochemical Company, with all technical parameters meeting the design requirements; it is capable of treating 7,000 tons of alkaline slag wastewater per year. Under the action of high-temperature and high-pressure catalysts, the high-concentration pollutants in refinery alkali slag wastewater, such as organic substances, sulfides, and phenols, are oxidized and decomposed into carbon dioxide, sulfates, and biodegradable substances, achieving a COD removal rate of 75%. 1.4 Photocatalytic technology: The superiority of TiO2 nanoparticles in the photocatalytic treatment of wastewater is now widely recognized. However, how to apply TiO2 to the industrial treatment of wastewater containing hard-to-degrade toxic organic compounds remains a bottleneck in the development of photocatalytic technology in the field of environmental protection. The research on the complete set of technologies and equipment for the photocatalytic treatment of wastewater containing refractory and toxic organic pollutants using TIO2 whiskers, carried out by the School of Chemical Engineering at Nanjing Tech University, has solved this problem. Through sintering and ion exchange methods, this project successfully developed a continuous photocatalytic wastewater treatment agent with a microscale size on the outside and a nanoscale size on the inside. The wastewater treatment efficiency of continuous photocatalytic wastewater treatment devices using TIO2 whisker catalysts is affected by issues such as the difficulty in separating and recovering components, as well as challenges in industrialization compared to pilot-scale tests. Using TIO2 whiskers for the photocatalytic degradation of printing and dyeing wastewater, it is possible to reduce the COD of untreated printing and dyeing wastewater to below 50 mg/L, with a colority of less than 40 times (based on dilution factors), and to convert large molecular organic compounds such as benzene rings into olefinic compounds. 1.5 Complexation adsorption technology: Jiangsu Nanda Gold Environmental Protection Technology Company has developed a new type of complexation adsorption resin that can be regenerated through hot water, **reducing the costs associated with the treatment of chemical wastewater and its recycling. The company has built 30 demonstration projects using this new type of adsorption material; with an annual treatment capacity of 3×106 tons of chemical wastewater, it is possible to recover approximately 4×106 tons of chemical raw materials from this wastewater. Compared with similar foreign products, the newly developed chelating adsorbent has approximately doubled the adsorption capacity for aromatic sulfonates, and its resin strength is over 50% higher. It successfully addresses the technical challenge of selectively adsorbing and separating aromatic sulfonic acid compounds in wastewater containing both polar organic solvents and inorganic salts (with a COD as high as 1.8×105 mg/l). By developing various separation processes, the value of the recovered materials can offset or partially cover the operational costs, and even result in a profit. Currently, this technology has been licensed to several domestic manufacturing enterprises. 1. A membrane treatment system capable of processing 3×104 tons of petrochemical wastewater per day has been put into operation at a Sinopec subsidiary. The construction of this system was carried out by the American company CNC Technologies and Beijing Sains Technology Company; the immersed dual-membrane method was used for the treatment of industrial wastewater. The difference between this technology and the external dual-membrane method is that there is no need for chemical flocculation or sand filtration of the wastewater; instead, the ultrafiltration membrane is directly immersed in the industrial wastewater. After primary treatment, reverse osmosis membranes are used for secondary treatment, and the resulting water can be reused in the production process. This method features a short process flow, low operating costs, a long service life for the system, and easy maintenance. Luyang Petrochemical Plant has successfully used membrane systems from Singapore’s Novellus Company to treat chemical fiber wastewater, with a designed wastewater reuse capacity of 200 T/H. The quality of the treated wastewater has reached or exceeded the standards for water used in recirculation processes, thus achieving the goal of reusing water from the fiber industry. 1.7 Multi-effect evaporation wastewater reuse technology: Wastewater treatment in propylene oxide production is a global challenge. There are more than a dozen propylene oxide manufacturers in the country, all of which use the chlorohydrin process; the wastewater containing calcium chloride generated during production corrodes equipment and causes severe environmental pollution. At present, Guoxian treats such wastewater by diluting it with fresh water before carrying out biochemical treatment; 1.5 tons of fresh water are required to treat 1 ton of wastewater. Moreover, the treated wastewater cannot be reused due to its high concentration, resulting in serious waste of water resources. Shandong Dongda Chemical Co., Ltd. and Guangzhou Huanwandai Environmental Engineering Co., Ltd. jointly invested in, designed, and constructed a wastewater reuse facility, where the epichlorohydrin saponification wastewater is subjected to multi-effect evaporation to concentrate the calcium chloride in it to 65%-70% (by mass), and the resulting product is then sold. After the implementation of this project, 6,000 t2 of dilution water is saved per day. 2.1 Strain selection technology: The research project on the use of artificially fixed engineered bacteria for treating oily wastewater, carried out by Harbin Institute of Technology, has been approved. Oil-containing wastewater mainly comes from the oil extraction and refining processes in the petrochemical industry. Currently, the conventional \"old three-stage\" process is used to treat oily wastewater, namely oil separation -- primary air flotation and secondary air flotation -- biological treatment. The artificially immobilized engineered bacterium oil removal device can be used as a substitute for secondary air flotation for heavy oil. The oil separation stage in the traditional three-stage process can only remove heavy oil from water; in such cases, secondary air flotation is required. However, the secondary air flotation process is complex, involves high investment and operating costs, and is difficult to manage. The artificially immobilized engineered bacterium oil removal device involves introducing engineered bacteria into oily wastewater; through water circulation, these bacteria adhere to activated carbon and become immobilized there. These engineered bacteria use oil in water as a nutrient, and through metabolic processes they break down the oil into carbon dioxide and water, thereby achieving oil removal. The artificially immobilized engineered bacteria oil removal device optimizes the traditional oil removal process; it features high efficiency and stable performance, while also reducing capital investment by 36% and operating costs by 33% compared to two-stage air flotation, thus holding broad application prospects. The Chengdu Institute of Biology, Chinese Academy of Sciences, has identified several highly effective functional microorganisms. It has developed multiple strains of microbial agents suitable for treating wastewater from industries such as petrochemicals and textiles, as well as corresponding high-density fermentation processes. A scaled-up production line for these microbial agents has been established, and they have been tested in oil refinery wastewater treatment projects. Molecular biology methods for monitoring and regulating microbial populations in wastewater treatment systems have been developed. Innovative achievements have been made in areas such as the structural design of anaerobic-aerobic hybrid bioreactors, the formulation of microbial agents, the preparation of polymer carriers, and the integration of reactor technologies with microbial carrier systems. The biological bed treatment technology and equipment for refinery wastewater, jointly developed by the Engineering Research Institute of Luoyang Petrochemical Engineering Company, Tianjin University, and the Luoyang branch, utilize efficient microbial strains as well as multi-guiding cylinders and a biological fluidized bed reaction technology with a low height-to-diameter ratio. The various discharge parameters after treatment meet standards exceeding those specified for grade 1 **discharge in the refinery industry; in particular, it achieves a high removal rate for ammonia and chlorides. The biological fluidized bed system features a simple process flow, small footprint, and low treatment costs, making it suitable for industrial use in coal enterprises and conducive to large-scale adoption. Researchers from Tsinghua University, the Chengdu Institute of Biology of the Chinese Academy of Sciences, and Tongji University used bio-self-immobilization technology to isolate and select a strain of bacterium effective at degrading oil and fat-based industrial wastewater, one strain effective at degrading pharmaceutical wastewater, and two strains effective at degrading coking wastewater. The engineered bacteria exhibit strong capacity for degrading pollutants; after self-immobilization, they can be effectively retained in the reactor while maintaining their degradation activity. They also isolated and screened 8 strains of efficient bacteria capable of degrading petrochemical and chemical fiber wastewater, and developed special biological fillers suitable for the attachment of these efficient bacterial strains. Furthermore, they developed screening and cultivation techniques for sulfate-reducing bacteria for high-sulfur organic industrial wastewater, and isolated 5 strains of anaerobic desulfurization bacteria capable of improving the biochemical treatability of the wastewater and achieving optimal desulfurization effects. A total of 7 demonstration projects and 2 pilot plants were built as part of this initiative. Once these facilities were put into operation, they solved the problem of wastewater treatment for the enterprises involved, with all performance indicators exceeding the requirements set for wastewater discharge; moreover, they reduced the costs associated with construction and operation. 2.2 Bioenhanced (QBR) technology: Refinery alkali sludge wastewater is a highly alkaline, high-concentration organic wastewater that is difficult to biodegrade; it is generated in refineries during the processes of electric refining of oils and desulfurization of alcohols. This wastewater contains large amounts of neutral oils, organic acids, as well as toxic and harmful pollutants such as volatile phenols and sulfides. Due to the high concentrations of pollutants (COD of approximately 2×105 mg/L, volatile phenols and sulfides of about 3×104 mg/L, and a salt content of over 150 mg/L), conventional methods are insufficient to meet the treatment requirements. Laiter Chemical Company of Dagang Oilfield in China National Petroleum Corporation uses the QBR technology developed through a collaboration between Beijing Jihongyuan Environmental Protection Technology Development Co., Ltd. and South Korea’s SK Group, which enables the removal of over 90% of the COD in high-concentration wastewater. QBR technology is a treatment method specifically designed for high-concentration, highly toxic organic wastewater. It applies modern microbial cultivation techniques to aerobic wastewater treatment systems, and through biological enhancement it enables a volumetric load that is 10 times higher than that achievable with conventional biological methods. This allows for the biochemical treatment of such high-concentration, highly toxic wastewater, thereby significantly reducing the costs associated with treating such wastewater. The capital investment and operating costs associated with the QBR technology are only a fraction or even a hundredth of those required for wet catalytic and incineration methods. It requires simple operation and management, delivers stable treatment results, and does not generate secondary pollutants such as waste gases or waste residues. Two demonstration units at Tianjin Dagang Petrochemical Company, with a processing capacity of 52 t/d each, for the comprehensive treatment of alkaline residues have been built and put into operation; they are capable of handling various types of alkaline residues, including those resulting from catalytic gasoline, coker gasoline, liquefied gas, and atmospheric diesel. It has currently been introduced to large and medium-sized domestic petrochemical enterprises and institutions such as Lanzhou Petrochemical, Jilin Petrochemical, Jinlin Petrochemical, Liaohe Petrochemical, and Shengli Refinery. The project \"Research on Utilizing Genetically Engineered Bacteria Fhhh for the Treatment of Petrochemical Wastewater through Cross-disciplinary Integration\", jointly carried out by Nanjing University, Yangzi Petrochemical, and ** University, is currently in the industrial implementation phase. The promotion and application of this achievement will open up a new path for wastewater treatment in China’s petrochemical and paper industries, including the production of purified terephthalic acid (PTA). This project integrates bioengineering, environmental engineering, and production techniques from the petrochemical and paper industries to pave a new path for wastewater treatment. This project integrates cutting-edge theories and advanced technologies from disciplines such as bioengineering, environmental engineering, ecotoxicology, and environmental information science. To address the pollution problem caused by PTA wastewater, genetically engineered mixed strains are used; as a result, the pollutant concentrations in the treated wastewater are below the **allowed emission standards, and its biological toxicity is significantly reduced. The project also developed environmental biotechnology information software with independent intellectual property rights. Comparisons with treatment data on PTA wastewater and domestic sewage published in the Netherlands and the United States showed that this software system possesses strong versatility, providing an effective tool for minimizing treatment efficiency, optimizing control decisions, and reducing treatment costs. Beijing Santai Zhengfang Bio-Environmental Technology Development Company has developed the 3T-IB immobilized microorganism technology for wastewater treatment, which exhibits unique effectiveness in dealing with high-concentration, hard-to-degrade organic wastewater. It is particularly effective in breaking down toxic and harmful macromolecular compounds that are difficult to degrade using traditional treatment methods, such as phenols (phenol, chlorophenol, cresol, nitrophenols, etc.), aromatic hydrocarbons (benzene, toluene, xylene, ***, phenolic substances, etc.), cyanides, and amines. The system features a high COD volumetric load and strong shock resistance, enabling direct biochemical treatment of organic wastewater with high concentrations. It has been successfully applied in numerous projects for treating such wastewater, including those in the petroleum, petrochemical, chemical, leather, gasification, food, brewing, household chemicals, printing and dyeing, biomanufacturing, and papermaking industries. Compared with traditional biological treatment technologies, this technology requires less investment, occupies less space, delivers better treatment results, has lower operating costs, and can save 30% on construction costs. Reduce operating costs by 30%–50%. 2.3 Aeration treatment technology: Lanzhou Jiehui Bio-Environmental Engineering Company has developed an aerated biological fluidized bed process that enables the reduction of the ammonia nitrogen concentration in wastewater from industries such as leather processing, papermaking, and printing and dyeing – where such wastewater is currently difficult to treat – from 600 mg/L to 15 mg/L, thereby meeting **first-class discharge standards. This technology was tested at Lanzhou Petrochemical Company for 3 years and finally succeeded; currently, the wastewater treatment plant with a capacity of 1.6104 mg/L is in operation. South China University of Technology, Soochow University, and Zhanjiang Dongxing Petrochemical Enterprise Co., Ltd. jointly completed a project on the industrial application of biotechnology for treating high-concentration organic wastewater from petrochemical enterprises. The bio-oxidation treatment process developed – the Isolated Aeration Biofilter (BAF) technology – was applied to the treatment of high-concentration organic wastewater from refineries, resulting in removal rates of 70%-90% for COD, 60% for BOD5, 80% for sulfides, and 85% for phenols. The effluent thus meets the standards for **secondary discharge. In addition, the researchers on this project have also developed a new type of bioreactor that utilizes a unique isolation aeration technique. Compared with the current biological treatment reactors in China, this bioreactor features high treatment efficiency, low investment costs, low operating expenses, and small floor space requirements; it represents an efficient and resource-saving biochemical wastewater treatment technology. 2. 4MBR Technology: MBR technology is an efficient water treatment process that combines biological degradation with the high-efficiency separation function of membranes. By using this technology, it is possible to retain all microorganisms in the bioreactor, thereby minimizing the organic pollution content in the treated water. It features a simple process flow, high efficiency, easy operation, ease of automated control, low investment costs, and stable water quality, making it highly suitable for wastewater treatment and reuse. Since the adoption of the MBR-based wastewater treatment process in the United States, it has received significant attention in the field of water treatment. The scale of its use in countries such as the United States, Japan, Germany, France, and Canada continues to increase, with the treatment capacity rising from 103 mg/L to 100,003 mg/L. The range of wastewater types that can be treated is also expanding; in addition to treating and reusing domestic sewage, it has been successfully applied to the treatment of industrial wastewater such as that from the food industry, fish processing, aquaculture, cosmetics production, dye manufacturing, petrochemical industries, as well as landfill leachate. The Microbiology Center of the Oil Production Technology Research Institute at Shengli Oilfield conducted research on treatment technologies and processes for reinjection wastewater from low-permeability oil fields using MBR, achieving good results. Field tests show that the final water quality can reach the A2 level specified in the \"Recommended Standards and Analysis Methods for Water Quality Used in Water Injection in Clastic Rock Reservoirs\". Domestic enterprises related to PTA, such as polyester manufacturers, generate large amounts of PTA-containing wastewater, which not only pollutes the environment but also wastes resources. Nanjing University of Technology’s \"highly efficient combined process for treating PTA wastewater using MBR\" can significantly reduce water consumption costs in these industries, while also generating substantial economic benefits. This combined treatment process and apparatus for PTA wastewater, which uses MBR as the core unit along with chemical catalytic oxidation, effective microbial strains, and biological fixation as auxiliary units, employs a catalytic oxidation process in which activated carbon serves as the main catalyst and air as the oxidant to treat PTA wastewater. This approach can effectively reduce the COD level in PTA wastewater, and it also enables the catalytic oxidation of large organic molecules into smaller ones, thereby increasing the biodegradability of the wastewater on an annual basis. Activated carbon, along with various powdered inorganic microorganisms, can be used as a support to increase the residence time of these microorganisms. It can also be employed as a coating material for membranes, thereby reducing membrane fouling and extending their service life. The water quality of the effluent treated by this process can meet the **first-class standards for comprehensive wastewater discharge. Moreover, it requires 40% less floor space compared to existing traditional treatment processes and equipment for PTA wastewater, the hydraulic retention time is reduced by over 50%, and the operating costs are lowered by approximately 20%. To consolidate its achievements in ensuring standardized wastewater discharge, Sinopec Balin Branch upgraded its wastewater treatment system by employing the advanced patented MBR technology (a combination of high-efficiency membrane separation technology and activated sludge process), thereby establishing Asia’s largest MBR facility with a capacity of 7.2 kt/d. Combining biological and physicochemical methods, as well as electro-biological coupling technologies, this system is effective in handling various substances such as halophenols, halohydrocarbons, and reactive dyes – all of which are important industrial raw materials or products, but are difficult to degrade by microorganisms. In the past, the treatment of such wastewater has always been a challenge for enterprises. Through in-depth research, the Institute of Process Engineering of the Chinese Academy of Sciences developed electro-biological coupling technology, which uses electrocatalytic reactions to catalytically reduce (or oxidize) recalcitrant organic substances in water into organic molecules that are easily biodegradable, with microorganisms then removing them completely in the same reactor. Taking wastewater with a *** mass concentration of 100 mg/L as an example, after 10 hours of treatment, the removal rate of *** is greater than 98%, and the removal rate of COD is greater than 90%; the effluent meets the ** discharge standards. 3.1 Chemical simulation biodegradation treatment technology: After 5 years of conducting numerous experiments on wastewater from papermaking, starch, alcohol, and other industries, Guangxi Ligui Environmental Protection Technology Company has successfully developed a comprehensive technology for treating wastewater through chemical simulation biodegradation. This technology combines microbial methods with comprehensive wastewater treatment techniques. This technology utilizes self-developed reversible redox \"actives\" to degrade organic matter in a chemically simulated biodegradation tank; thereafter, electrochemical techniques are employed to further degrade the wastewater organically. Electrochemical methods are also used to carry out forced treatment and decolorization of the wastewater, thereby achieving good wastewater treatment results. Industrial tests of this technology were carried out using the papermaking black liquor from Guigang Hongqi Paper Co., Ltd., and it has been operating satisfactorily for over a year. 4 Conclusion: Wastewater treatment technologies are evolving toward being more efficient, compact, specialized, and diverse. The selection of highly effective microbial strains for treatment and the use of efficient bioreactors remain key areas of development. For treating wastewater that is difficult to biodegrade, combining such methods with biochemical treatment techniques as well as photocatalytic techniques will continue to be areas of research. Introduction to Oil-Contaminated Wastewater Treatment Technologies Abstract: This paper introduces the principles and characteristics of common oil-containing wastewater treatment technologies as well as the equipment used for oil removal, and provides an overview of the methods for treating oil-contaminated wastewater. Keywords: oily wastewater; technologies; wastewater treatment methods. Oily wastewater is generated in large quantities and across a wide range of industries; for example, it is produced during oil extraction, petroleum refining, petrochemical processing, oil storage and transportation, oil tanker accidents, ship navigation, vehicle washing, machinery manufacturing, food processing, and other processes. Oil pollution, as a common type of pollution, poses a severe threat to environmental protection and ecological balance. There are many oil-water separation techniques available today; common methods include gravity separation, air flotation, coarsening, filtration, adsorption, ultrasound, and other approaches. Moreover, new oil removal technologies are continually being developed. This article introduces the principles and methods of oil removers. 1 Gravity separation method: The gravity separation method is a typical primary treatment technique that takes advantage of the density difference between oil and water as well as their immiscibility to separate oil droplets, suspended particles from water, whether in a stationary or flowing state. Oil droplets dispersed in water rise slowly upward due to buoyancy and separate into layers; the rising speed of these oil droplets depends on the size of the droplets, the density difference between oil and water, the flow conditions, and the viscosity of the fluid. The relationship between them can be described by laws such as Stokes' and Newton's laws. 1.1 Transverse flow oil remover: The transverse flow oil removal equipment for oily wastewater was developed on the basis of the inclined plate oil remover; it consists of a coagulation zone and a separation zone for the oily wastewater. The oily wastewater first passes through a cross-plate type coalescer, where small, dispersed oil droplets combine to form larger ones, and small solid particles aggregate into larger particles. The resulting larger oil droplets and solid particles then pass through a transverse flow separation plate section with unique channels, thereby being separated from the water. While separating oil from water and solid substances, gas (natural gas) can also be separated. 1.2 Principle of oil removal in corrugated plate coalescing oil-water separators: The principle behind oil removal using corrugated plates relies on the density difference between oil and water, which causes oil droplets to float to the peaks of the plates and thus be separated and removed. The key lies in applying the Hazen-Williams shallow tank settlement principle to create corrugated plates with varying spacing and flow patterns; as a result, the cross-sectional area through which water flows changes, and the water flow alternates between expanded and contracted states, generating pulsating (sinusoidal) flow. This increases the probability of collisions between oil droplets, helps larger oil droplets form from smaller ones, and accelerates the upward movement of oil droplets, thereby achieving oil-water separation. 1.3 Aggregated oil-water separators: The Austrian company Feere was the first in the world to develop the CPS integrated corrugated plate gravity-accelerated aggregated oil-water separator. This corrugated sheet is a patented product of Ferre Company; it is made from polypropylene as its base material and contains various additives that endow it with oil-affinity without sticking to oil, as well as anti-aging properties. The corrugated plates are stacked one on top of another, with a spacing of generally 6 mm (when the concentration of suspended particles in the water is high, a spacing of 12 mm can be used). 1.4 The high-efficiency upward-angled free water separator combines horizontal and vertical free water separators, employing an upward-angled design to overcome the disadvantages of a small oil-water interface area in vertical containers, as well as the short distance between the oil-water interface and the water outlet in horizontal containers, which results in insufficient separation time. The liquid inlet is located at the upper end of the tubular container; oil droplets in the water can coalesce and rise to the upper oil outlet, while the water sinks to the lower water outlet for discharge. The elevation angle of this device is less than 12°; it is 18.3 m long, and available in two sizes with diameters of 1,372 mm and 914 mm. 2 Filtration method: The filtration method involves passing wastewater through a device with pores or through a filter layer made of certain particulate media; the retention, screening, and inertial collision effects of these elements are used to remove harmful substances such as suspended solids and oils from the wastewater. There are 3 common filtration methods: stratum filtration, membrane filtration, and fiber media filtration. Membrane filtration, also known as membrane separation, uses microporous membranes to retain oil droplets and surfactants, and is primarily used to remove emulsified oils and certain dissolved oils. Filter membranes include ultrafiltration membranes, reverse osmosis membranes, and hybrid filter membranes, among others. Membrane materials are divided into organic membranes and inorganic membranes. Common organic membranes include cellulose acetate membranes, polysulfone membranes, polypropylene membranes, etc., while common inorganic membranes include ceramic membranes, alumina, cobalt oxide, titanium oxide, etc. The emulsified oil is in a stable state, and it is difficult to separate it using physical or chemical methods. With the rapid development of membrane science, the use of membrane processes for treating emulsified oil wastewater has gradually been accepted and applied in industry. 3 Centrifugal separation method: The centrifugal separation method involves spinning a container containing oily wastewater at high speed to create a centrifugal force field. Due to the different densities of solid particles, oil droplets, and wastewater, they experience varying levels of centrifugal force, which enables the removal of solid particles and oil droplets from the wastewater. The commonly used device is a hydrocyclone separator. The application of cyclone separators in liquid-solid separation dates back to the 1840s, and they are now quite mature; however, research in the field of oil/water separation began much later. Although the basic principles of liquid-solid separation and liquid-liquid separation are the same, the geometric structures of their respective equipment differ significantly. The oil-removing cyclone separator originated in the UK. Starting from the late 1960s, the Multiphase Flow and Mechanical Separation Laboratory led by Professor Martin Thew at the University of Southampton in the UK began research on oil removal vortex separators for water, and invented a double-cone, dual-inlet liquid-liquid vortex separator. Satisfactory results were achieved during the testing process. Subsequently, Young GAB and others designed a single-cone cyclone separator that possesses the same separation performance as the biconic cyclone but has a processing capacity twice as high. Through geometric optimization, Conoco developed the K-type cyclone separator, which exhibits a more significant improvement in the separation performance of oil droplets with diameters less than 10 μm. Due to the many unique advantages of cyclone separators, cyclone oil removal technology has become an irreplaceable standard device for treating oily wastewater in developed countries, especially on offshore oil drilling platforms. 4 Flotation method: The flotation method, also known as air flotation, is a water treatment technique that is being extensively studied and increasingly applied both domestically and internationally. This method involves introducing air or other gases into water to create tiny bubbles, which allow small suspended oil droplets and solid particles in the water to attach to these bubbles and rise to the surface along with them, forming a scum layer (an oil-containing foam layer). Afterwards, an appropriate skimmer is used to remove the oil. This method is primarily used to treat dispersed oil, emulsified oil, and fine suspended solids with particle sizes of 10–60 μm that remain in water after treatment in oil separation tanks; the oil content in the effluent can be reduced to 20–30 mg/L. Depending on the method used to generate bubbles, air flotation is divided into pressure dissolved air flotation, air sparging flotation, electrolytic flotation, etc., among which pressure dissolved air flotation is the most widely used. 5 Biological oxidation method: The biological oxidation method is a technique that uses the biochemical actions of microorganisms to purify wastewater. Oils are hydrocarbon-based organic substances that can be broken down into carbon dioxide and water through biological processes such as the metabolism of microorganisms. The organic substances in oily wastewater exist mainly in dissolved and emulsified forms, with a high BOD5 value, which facilitates biological oxidation. For wastewater with an oil mass concentration of 30–50 mg/L or less, and which also contains other biodegradable harmful substances, biochemical treatment is commonly used, primarily to remove the dissolved oil in the wastewater. Common biochemical treatment methods for oily wastewater include the activated sludge process, biological filtration, and rotating biological contactors. The activated sludge process offers good treatment efficiency and is mainly used to treat wastewater with high requirements and stable water quality. Compared with the activated sludge process, in the biofilm process, biofilms adhere to the surface of packing media, allowing microorganisms with a slow reproduction rate to survive as well, thereby forming a stable ecosystem. However, since it is difficult to control the amount of microorganisms attached to the surface of the carrier, its operational flexibility is low, and the volume load is limited. 6 Chemical method: The chemical method, also known as the reagent method, is a technique in which reagents are added to convert the pollutant components in wastewater into harmless substances through chemical reactions, thereby purifying the wastewater. Common chemical methods include neutralization, precipitation, coagulation, oxidation-reduction, etc. Coagulation is mainly used for oily wastewater. The coagulation method involves adding a certain proportion of flocculants to oily wastewater; these flocculants hydrolyze in water to form positively charged aggregates that neutralize the negatively charged emulsified oil. As a result, the oil particles aggregate and their size increases. At the same time, flocs are formed that adsorb the smaller oil droplets, and oil and water are then separated through sedimentation or flotation. Common coagulants include inorganic coagulants such as polyaluminum chloride (PAC), ferric trichloride, aluminum sulfate, and ferrous sulfate, as well as organic polymer coagulants such as acrylamide and polyacrylamide (PAM). Different coagulants require different dosages and have varying suitable pH ranges. This method is suitable for oil droplets in an emulsified state and other fine suspended particles that cannot be separated by gravity settling. 7 Adsorption method: The adsorption method makes use of lipophilic materials to adsorb dissolved oils and other soluble organic substances in wastewater. The most commonly used oil-absorbing material is activated carbon, which can adsorb dispersed oil, emulsified oil, and dissolved oil in wastewater. Due to its limited adsorption capacity (typically 30–80 mg/g for oils), high cost, and difficulty in regeneration, activated carbon is generally used only as the final stage in the multi-stage treatment of oily wastewater, enabling the oil concentration in the treated water to be reduced to 0.1–0.2 mg/L. In 1976, the Changling Refinery in Hunan adopted activated carbon adsorption for advanced treatment in its wastewater processing. Some useful results have also been achieved domestically and internationally in the development of new adsorbents. Research has found that flake graphite can adsorb the heavy oil released by offshore oil tanker spills and easily separate from water. Adsorption resins are a new type of organic adsorbent that have been developed in recent years. They possess excellent adsorption properties and are easy to regenerate; as a result, they are gradually replacing activated carbon. An increasing number of industry professionals are researching the synthesis and application of high-efficiency oil-absorbing resins. Studies have shown that the use of polypropylene oil-absorbing materials to adsorb, separate, and recover oily substances from oily industrial wastewater allows for the selection of appropriate purification methods based on factors such as the initial condition of the wastewater, the desired final outcome, and the flow rate of the water. In addition, coal ash, modified bentonite, sulfonated coal, crushed coke, organic fibers, oil-absorbing felt, ceramic particles, quartz sand, wood chips, straw, and the like can also be used as oil-absorbing materials. Once the oil-absorbing material has reached saturation, it can be regenerated and reused depending on the specific circumstances, or it can be used directly as fuel. 8 Coarsening method: The coarsening method takes advantage of the significant difference in the affinity between oil and water for cohesive materials; oil particles are captured by these materials and remain on their surfaces and within their pores, forming an oil film. When this oil film reaches a certain thickness, it breaks away under the effects of hydraulic forces and buoyancy, and then combines to form larger oil particles. According to Stokes’ law, the rising speed of oil particles in water is proportional to the square of their diameter. After coalescence, oil droplets with larger particle sizes are easier to separate from water. The wastewater after coarsening retains the same oil content and properties of the oily substances; it simply becomes easier to remove the oil using gravity separation methods. 8.1 The swirl oil removal, coarsening oil removal, and inclined plate oil removal technologies of the new type of high-efficiency oil removers are widely regarded as efficient oil removal techniques today. A high-efficiency oil remover is a device that integrates various of the aforementioned high-efficiency oil removal techniques into one unit; its overall structure is designed to be horizontal, and it consists of a swirl (vortex) section for coarse particle separation, as well as an inclined plate section for oil removal. It not only improves oil removal efficiency, but also is easy to operate and requires less space. Based on the characteristics of the produced water from the Jianghan Oilfield, two-stage coarsening and two-stage inclined plate oil removal are employed; when the inlet ρ (oil) is ≤1,000 mg/L, the outlet value meets the requirement of the subsequent treatment equipment (filters), namely ρ (oil) ≤30 mg/L. 8.2 EPS oil-water separation technology The EPS oil-water separator is a highly efficient and advanced device for separating oil from water. It integrates modern advanced plate-based oil removal and coagulation technologies, combining functions such as pretreatment of wastewater, oil-water separation, secondary sedimentation, and oil recovery. It features low installation and operation costs, excellent oil-water separation performance, and easy operation and maintenance. It serves as an upgraded alternative to vertical oil removal tanks and inclined plate oil removal systems such as the American Petroleum Institute’s oil removal system (API), the corrugated plate/inclined plate oil removal system (CPI), and the parallel inclined plate oil removal system (PPI). The EPS oil-water separator has been put into practical use in countries such as South Korea, the United States, Poland, India, Thailand, and China, with generally good results in wastewater treatment. 9 Sound wave, microwave, and ultrasonic dehydration technologies: Sound waves can accelerate the coalescence of water droplets, thereby improving the efficiency of crude oil dehydration; ultrasonic waves can reduce energy consumption and the amount of demulsifiers required; while microwaves not only decrease the stability of emulsions but also heat them, further promoting the coalescence of water droplets. These technologies hold great potential for addressing the problem of deep dehydration in old oil fields in eastern China, where the complex properties of crude oil result from various extraction methods. Microwaves refer to electromagnetic waves with frequencies ranging from 300 MHz to 300 GHz. Microwave water treatment technology is a novel approach to water treatment that utilizes the strong catalytic effect, penetration capability, selective energy supply, and microbial killing properties of microwave fields on the physicochemical reactions in single-phase and multiphase flows. Ultrasonic waves are high-frequency mechanical waves, with frequencies generally ranging from 2×104 to 5×108 Hz. They possess characteristics such as concentrated energy and strong penetration power. Ultrasonic waves in water can cause coalescence effects, as well as cavitation or voiding effects. When ultrasound passes through a solution containing wastewater, it causes the tiny oil droplets to vibrate along with the water. However, due to the different relative vibration speeds of particles of varying sizes, the oil droplets will collide with each other and stick together, resulting in an increase in the volume of the oil droplets. Subsequently, as the particles have grown larger and can no longer vibrate with the sound waves, they move in a random manner. Finally, the small oil droplets in the water coalesce and rise to the surface, resulting in good oil-water separation. When using ultrasound to treat emulsified oil wastewater, it is necessary to conduct experiments first to determine the optimal sound frequency; otherwise, an ultrasonic crushing effect may occur, affecting the treatment efficiency. To date, scholars at home and abroad have used ultrasound technology to remove dozens of pollutants from water. However, the systems studied are mostly single-component simulation systems, whereas actual wastewater often contains multiple pollutants; therefore, the applicability of ultrasound technology in practical wastewater treatment still requires further research. Furthermore, current research on the use of ultrasound technology to degrade pollutants in water is mostly at the laboratory stage. Due to insufficient research on aspects such as the degradation mechanism of acoustic chemical reactions, reaction kinetics, and the design of reactors for scale-up, it is still difficult to implement this technology on an industrial scale. 10 The ultrasound/electrochemistry combined technology utilizes the cavitation effect of ultrasound to prevent the formation of a coating on the electrodes during electrochemical reactions, thereby avoiding a decline in electrode activity. The ultrasonic cavitation effect also facilitates the generation of ·OH radicals in the electrocatalytic process, accelerating the decomposition of pollutants in wastewater. Additionally, ultrasound helps to disperse organic substances thoroughly in aqueous solutions, thus significantly improving the treatment capacity of the reactor. Mizera et al. found that when electro-oxidative treatment was used on phenol-containing wastewater, the decomposition rate was only 50% in the absence of ultrasound; however, when ultrasound with a frequency of 25 kHz and an intensity of 104 W/m2 was used, the decomposition rate of phenol increased to 80%. Liu Jing et al., using the ultrasound/electrochemistry combined technique for the treatment of printing and dyeing wastewater, found that under the combined action of ultrasound and an electric field, the decolorization rate of the wastewater was **higher than that achieved when ultrasound was used alone. 11 Conclusion Oil-water separation technology is one of the key techniques for treating oily wastewater at present. The methods mentioned above each have their own applicable ranges; different treatment methods should be employed depending on the properties of the various types of oils and the requirements regarding water quality. The various processing units mentioned above do not appear alone in the treatment of oily wastewater; since oil particles in wastewater are mostly present in a concentrated state simultaneously, and rarely in a single state, a multi-stage treatment process is employed for such wastewater. Only through sequential treatment using multiple processing units can the wastewater meet the standards for discharge or reuse. References: Chen Zhongxi, Deng Shubo, Xia Fujun. Research on the use of horizontal flow oil removers for treating oil field wastewater. Industrial Water Treatment, 2001, 21(1): 31-33. Wang Min, Yang Changzhu, Yan Li, et al. Research on corrugated plate coalescing oil-water separators. Transportation Environmental Protection, 2004, 25(1): 26-28. Zhang Chunlin, Zhang Xujun. Experimental studies on the application of new types of oil-water separators in oil field wastewater treatment. Environmental Protection in Petrochemical Industry, 2003, 26(1): 30-33. Zhuang Jianyuan, Wang Guoli, Weng Weilong. Development trends in surface processing technologies for oil and gas fields abroad. Petroleum Planning and Design, 2003, 14(1): 45-53. Wang Shengchun. Application of polypropylene hollow fiber microporous membranes in the treatment of oily wastewater from oil fields. Membrane Science and Technology, 1998, 18(2): 28. Sang Yimin, Li Fasheng, He Xuwen, et al. Properties of oily wastewater and its treatment technologies. Chemical Engineering Environmental Protection, 2004, 24(Suppl): 94-97. Feng Guobin. Development and application of a new type of high-efficiency oil remover. Industrial Water and Wastewater, 2003, 34(5): 69-72. Wen Qinxue, Wu Bin, Wen Yan, et al. EPS oil-water separation technology and its applications. Water Supply and Drainage, 2003, 29(1): 43-45. Peng Qingtao, Wang Li, Hu Wenxiang. Water treatment technologies using microwaves, ultrasonic waves, and composite electromagnetic fields. Environmental Protection, 2004, (3): 20-23. Yu Jianfeng. Treatment of oily wastewater. Filtration and Separation, 1999, (4): 20-24. Source: Gutengshui Network. Authors: Li Bo, Zhou Shijun. Technologies for re-injection of oil production wastewater. After dehydration, the water containing crude oil usually contains certain amounts of oil, sulfides, organic phenols, cyanides, bacteria, solid particles, as well as chemical agents such as demulsifiers, flocculants, and disinfectants added during treatment. In the middle and later stages of oil field development, the reservoir pressure drops significantly, and water injection for oil production is an important method to maintain this pressure. The large-scale discharge of produced water not only causes environmental pollution but also wastes valuable water resources. Therefore, reinjecting treated oil production wastewater is an important approach to reducing environmental pollution, ensuring the sustainable development of oil fields, and improving their economic efficiency. Suspended solids and oil in wastewater are two major factors that cause blockages in water injection wells and oil reservoirs during the reinjection of oil production wastewater. The oil removal process often involves the removal of suspended solids as well; therefore, the issue of oil removal from oil production wastewater has become an important topic of research in wastewater reinjection treatment. 1. Treatment technologies for oil production wastewater: Based on the five forms in which oil exists in such wastewater, the main treatment methods are as follows: 1.1 Oil separation method – This method primarily removes oil in its free state and mechanically dispersed form, through natural flotation separation. Common types of treatment structures include horizontal flow oil separators, flat plate oil separators, inclined plate oil separators, etc. 1.1.1 Parallel-flow oil separator (API): The treatment process in a parallel-flow oil separator relies on gravity to separate oil from water. Proper hydraulic design and wastewater retention time are two important factors affecting oil removal efficiency. The longer the residence time, the better the oil removal effect. 1.1.2 Compared with parallel flow oil separators (PPI) and corrugated plate oil separators (CPI), the difference between these two types of oil separators lies in the use of inclined parallel plates or corrugated inclined plates installed along the direction of water flow in the separation tank. These partitions can effectively shorten the vertical rising distance of oil droplets, causing them to aggregate into larger drops on the lower surface of the inclined plate. This not only increases the effective separation area but also improves the flow rectification effect. Its advantages are small floor space, good oil-water separation, short residence time, and low investment cost. The treatment results of oil-containing wastewater with low oil content show that API-type oil separators are superior to CPI oil separators. 1.2 According to the method of bubble generation, air flotation can be divided into pressurized dissolved air flotation (DAF), impeller air flotation (IAF), aeration flotation, induced draft air flotation, electrolytic flotation, etc. Air flotation is often used as a secondary treatment technique. To ensure optimal oil removal, flocculation must be combined with it; for the removal of colloidal and emulsified oils, the chemical treatment step in the DAF process is very important. 1.3 Coagulation filtration method The oil removal mechanism of coagulation filtration is a combination of two mechanisms: the coagulation of small oil droplets and the direct removal of large oil droplets. It achieves good effluent quality under appropriate conditions, and is particularly suitable for the treatment of wastewater containing mechanically dispersed oils. However, the treatment efficiency of oil-containing wastewater of different types varies greatly; in particular, for wastewater with low oil content, a single coagulation-filtration method is not suitable for treatment. 1.4 Chemical treatment methods and electrolytic methods: Chemical treatment methods are mainly used to remove emulsified oil. Generally, chemical agents are used directly to weaken the stability of the dispersed oil droplets. Inorganic coagulants are usually added, often aluminum salts and iron salts, and then the separated oil is removed through sedimentation or air flotation. After adding a coagulant, the efficiency of oil removal by air flotation can be increased by 10% to 25%, with a maximum level of over 95% (Table 1). Table 1 Comparison of oil removal efficiency by flotation with coagulants file:///C:/Users/1/AppData/Local/Temp/ksohtml/wps_clip_image-2925.png The electrolytic method is effective in removing emulsified oil, and it does not cause secondary pollution. The electrolytic methods mainly include electrolytic air flotation and electrolytic flocculation. The former uses oxygen and hydrogen produced by water electrolysis to form microbubbles for air flotation. Due to their small size, these bubbles are capable of removing smaller oil droplets and suspended particles, allowing the treated wastewater to be reused for injection. The latter uses consumable electrodes; an applied voltage oxidizes the electrodes, thereby releasing metal ions. The hydrolysis products of the released metal ions have coagulating properties. The wastewater to be treated must have sufficient conductivity to enable the electrolytic cell to function properly and to prevent electrode passivation. 1.5 Biological treatment techniques: After being treated in an oil separator and by air flotation, oilfield wastewater can be processed using biochemical methods such as the activated sludge method, trickling filter method, aeration method, or contact oxidation method. A representative process flow is shown in Figure 1. There are also reports from abroad of further treatment using oxidation ponds after passing through API oil separators and air flotation units; the oil content in the water exiting the air flotation unit was 40 mg/L, and after a retention time of more than 20 days in the oxidation pond, the oil content in the effluent dropped below 18 mg/L. The Institute of Botany, Chinese Academy of Sciences, and the Jiangsu Institute of Botany used the water hyacinth ecological engineering to treat oil extraction wastewater. The results showed that the optimal control range was 65 mg/L < COD < 130 mg/L, while the critical value was COD = 262.6 mg/L. file:///C:/Users/1/AppData/Local/Temp/ksohtml/wps_clip_image-24346.png 1.6 Adsorption method: The adsorption method involves using lipophilic materials to absorb oil from water. Activated carbon is a commonly used adsorbent material. In addition, coal, oil-absorbing felt, ceramsite, quartz sand, wood chips, boron sludge, etc. can also be used as adsorbents. The activated carbon adsorption method is subject to certain limitations in its use due to high treatment costs and difficulties in regeneration. In recent years, it has gradually been used abroad for the advanced treatment of oily wastewater in order to meet increasingly stringent wastewater discharge standards. Japan is one of the countries that makes extensive use of granular activated carbon for advanced treatment; there are currently around 30 industrial installations in use. The United States is currently conducting technical research on the use of powdered activated carbon added to biochemical aeration tanks for treating oily wastewater. Research and practice on the use of granular activated carbon to treat oil production wastewater have also been carried out in China. As can be seen from Table 2, under very low oil content conditions, the oil removal efficiency of activated carbon is extremely high, reaching over 95%. 1.7 Membrane separation technology: In recent years, an increasing number of membrane separation technologies have been employed in the treatment of oil field produced water. Membrane separation technology is a technique that utilizes the selective permeability of membranes for separation and purification. When the particle size of oil particles in wastewater is in the micron range, mechanical methods can be used for pre-treatment. Membrane treatment allows for the appropriate determination of the molecular weight that the membrane can retain, based on the size of the oil particles in the wastewater. Generally, no phase changes occur during the treatment process; it operates at room temperature and boasts high efficiency, energy savings, low investment costs, and minimal environmental impact. The five membrane separation technologies commonly used in the treatment of oil production wastewater are reverse osmosis (RO), ultrafiltration (UF), microfiltration (MF), electrodialysis (ED), and nanofiltration (NF). ?Microfiltration is the most widely used due to its low pressure requirements, ease of cleaning, and low operating costs. When using microfiltration to treat oily wastewater, it primarily removes large particles and solid suspended matter from the wastewater, and can also serve as a pre-treatment step for ultrafiltration and reverse osmosis. Ultrafiltration membrane technology is currently the most widely used in the treatment of oily wastewater. Around 1991, the United States researched ceramic ultrafiltration membranes for treating produced water intended for reinjection in oil fields. There are reports of the application of ultrafiltration membrane technology in China’s Huabei Oilfield, Jianghan Oilfield, and Shengli Oilfield. Compared with traditional flocculation separation methods, the overall cost of ultrafiltration membrane treatment is lower. However, when treating oily wastewater with ultrafiltration membranes, the removal rates of BOD and COD are not high because low-molecular-weight substances can pass through the membrane; therefore, the ultrafiltration permeate is often subjected to further treatment via reverse osmosis (or biological methods such as activated sludge process) (Figure 2). file:///C:/Users/1/AppData/Local/Temp/ksohtml/wps_clip_image-30755.png The contamination and cleaning of ultrafiltration membranes are among the key issues in current research on ultrafiltration membrane technology. The Shanghai Institute of Nuclear Physics, Chinese Academy of Sciences, modifies the surface of ultrafiltration membranes by using surfactants in order to enhance the hydrophilicity of that surface, thereby effectively reducing contamination on it. The first large-scale application of reverse osmosis systems for the treatment of oil field produced water was at the Mt. Pose Co-generation Plant in California. Its water treatment system includes oil removal, clarification, filtration, and reverse osmosis desalination units; the treated water is used as feedwater for power plant boilers. This water treatment system successfully treats produced water with a salt content of 3000 mg/L, silicon levels of 6263 mg/L, oil content of 3.5 mg/L, and total organic carbon (TOC) levels of 16–23 mg/L, bringing it to the quality required for boiler water. Domestic patent reports indicate that combining salting-out with reverse osmosis for the treatment of emulsified oil wastewater yields good results. Since 1990, the Canadian Centre for Environmental Wastewater has been using electrodialysis to treat oilfield produced water, conducting a series of small-scale tests and overcoming two major challenges in scaling up to pilot scale: membrane fouling and the treatment of high-temperature produced water. 1.8 Efficient oil-water separation equipment: In recent years, driven by considerations regarding environmental protection and economics, many large oil companies abroad have developed various efficient oil-water separation devices in order to reduce high costs and the expenses associated with treating produced water. For example, the Canadian Engineering Research Centre (C-FER) has developed an underground oil-water separation system that combines hydrocyclone separators with an improved multi-flow underground pumping system, thereby enabling oil production, oil-water separation, and the reinjection of produced water back into the well. This new technology has been successfully applied in the Alliance oil field in Alberta, eastern Canada. 2 Current Status and Prospects of Oil Production Waste Water Treatment Technologies: Due to the varying environments in which oil fields are located, there are significant differences in the permeability of the reservoir rocks, which in turn results in different requirements regarding the quality of water used for reinjection. In foreign oil fields, the treated production water is primarily used for reinjection, followed by use in agricultural irrigation, as well as as feedwater for steam generators or boilers. At present, most oil fields in the country employ a three-stage treatment process that includes oil separation and removal – coagulation or sedimentation (or air flotation) – filtration, supplemented by treatments such as scale inhibition, corrosion prevention, sterilization, membrane treatment, or biochemical methods. Since the CODcr level of the produced water can sometimes be extremely high, especially for heavy oil wastewater, polymer-containing produced water, and highly saline produced water, the compliance rate after treatment before discharge is only around 50%. There are also many other reasons why the produced water cannot be reused and must be discharged externally. The traditional methods currently in use in China, though somewhat effective, still present many problems after treatment; for example, oil separation tanks can only remove large-sized oil droplets and cannot eliminate emulsified oil or dissolved oil in the water ； The flotation method requires the use of demulsifiers, and oil is not easy to recover ； The activated carbon adsorption method is costly, and activated carbon is difficult to regenerate ； Membrane treatment offers advantages such as high efficiency, compact equipment, low energy consumption, simple operation, ease of automation, and suitability for industrial-scale application. Coupled with the increasing focus and in-depth research on membrane treatment of oilfield produced water both domestically and internationally, continuous improvements in membrane materials, and gradual reductions in membrane costs, the use of membrane separation technology for treating oilfield produced water has become an important direction for future development. At the same time, other technical documents on the China Sewage Treatment Engineering Network can also be referred to. References: ??W. Patterson. Handbook of Industrial Water Treatment Techniques. Beijing: Chemical Industry Press, 1993.11:286–287. ??Yost, KJ., A. Solutions. Fin. Manag. Only, 1978:19–24. ??Beme, F., L.P. Aggarwal. Effluent Treatment in the Petroleum Industry. Effluent Water Treatment, 1974, 14:26–29. Morrison, J. Tilted-Plate Separators for Refinery Wastewater. Oil Gas Res., 1970, 68:86–88. Cawley, W., ed. Treatability Manual. Vol. IV. Technologies for Controlled Removal of Pollutants. Vsepa 600-8-80-042-C, 1980. Quiley, R.E., E.L. Hoffman. Floatation of Liquid Wastes. Proceedings of the 21st Industrial Waste Conference. Purdue University, 1966:527–533. Madian, E.S., et al. Treating of Produced Water for Surface Discharge at the Arun Gas Condensate Field. SPE Paper 28946, presented at the SPE International Symposium on Oilfield Chemistry, San Antonio, Texas, 1995. ??Tang Shuyu, Chen Jianguo, Shi Jianwen. Growth of Water Hyacinth in Refinery Wastewater and Its Purification Effect. Environmental Science, 1996, (1):44–46. ??Wu Dunhu, Lü Furong, Xu Tao, et al. Treatment of Oily Wastewater Using Boron Sludge. Water Treatment Technology, 1996, 22(2):113–118. Lan Shucheng. Activated Carbon Water Treatment Technology. Beijing: China Environmental Science Press, 1991:103. ??Chen, A.S.C., Flynn, J.T., Casaday, A.L. Removal of Oil, Grease, and Suspended Solids from Produced Water Using Ceramic Cross-Linked Microfiltration. SPE Production Engineering, 1991, (6):131–135. Wang Shengchun, Wen Jianzhi, Wang Hai, et al. Application of Polypropylene Hollow Fiber Microfiltration Membranes in the Treatment of Oily Wastewater from Oilfields. Membrane Science and Technology, 1998, 18(2):28–32. Gao Yiheng, Ye Lingbi. Fundamentals of Membrane Separation Technology. Beijing: Science Press, 1983. Zhou Keyuan. Applications of New Technologies in Environmental Protection. Beijing: China Environmental Science Press, 1990:21–33. Li Haijin. Current Development and Application Prospects of Downhole Oil-Water Separation Technologies. Foreign Petroleum Machinery, 1999, 9(5):50–59. Li Haijin. Application of Downhole Oil-Water Separation Technologies in the Alliances Oilfield. Foreign Petroleum Machinery, 1999, 9(2):31–35. Source: Gutengshui Network. Authors: Huang Tinglin, Yang Liwei. Discussion on the Development Trends in Petrochemical Wastewater Treatment. This article is sourced from “China Construction Abstracts”. Please cite the source via a link: http://www.863p.com/water/WaterSclgy/200611/15166.html. Article Summary: Currently, the development trends in wastewater treatment technologies for the petrochemical industry (including refineries) can be summarized in three points: strengthening pre-treatment, improving secondary treatment, and implementing complementary post-treatment measures. These are discussed as follows: I. Strengthening Pre-Treatment. Petrochemical wastewater comes in various types with complex compositions; some of it is highly toxic, inhibits biological degradation, or has high concentrations. If proper pre-treatment is not carried out, it will inevitably hinder or even disrupt the normal operation of wastewater treatment facilities. The importance of strengthening pre-treatment is increasingly recognized, and extensive experimental research has been conducted, leading to significant progress. Many effective pre-treatment technologies have been developed, ensuring the proper functioning of biological wastewater treatment systems. 1. Treatment of oily wastewater (including highly emulsified wastewater) (1) Research and application of polymer flocculants......