Support from domestic instruments: Application of domestic solutions for advanced treatment of petrochemical wastewater

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Petrochemical industry refers to an industry that uses natural gas as the main raw material, and employs various chemical processing techniques to obtain the desired resources. It is a sector with a large scale of operation and high production volumes; it also consumes and generates large amounts of water on a daily basis. Therefore, it is particularly important to ensure proper treatment of wastewater from petrochemical enterprises. Considering the nature and level of pollution emitted by petrochemical enterprises, different construction methods and the properties of raw materials have a decisive impact on the characteristics of the pollutants released. For dealing with the pollutants emitted by petrochemical industries, conventional wastewater treatment technologies are often insufficient; therefore, there is a need to develop innovative and technically advanced wastewater treatment processes. Advanced treatment processes: The wastewater discharged from certain petrochemical production facilities has a complex composition and significant fluctuations in quality; it is characterized by high levels of oil, ammonia nitrogen, phenols, and chemical oxygen demand. Therefore, the MBR process is chosen as a technology for advanced wastewater treatment; it exhibits significant effectiveness in removing COD and ammonia nitrogen, and helps prevent the accumulation of excessive biological sludge during the reuse of recycled water, which could otherwise cause pipe blockages and corrosion. It also has a good capacity to handle other pollutants, as well as strong resilience to changes in water quality. For the specific process flow, see Figure 1. 1. Grid: The grid should be installed at the wastewater inlet of the sewage treatment plant, or in front of the sewage lift pump. It is used to block large solid particles such as plants, trash, plastic, fibers, etc., in order to prevent clogging or damage to pumps, pipes, and subsequent equipment. 2. Sedimentation: Sedimentation tanks are generally classified into horizontal flow, vertical flow, combined flow, and inclined plate type sedimentation tanks. The primary sedimentation tank, serving as a primary treatment stage, is a pretreatment facility for biological treatment; it is the main device used to settle and separate the heavier suspended solids in wastewater. Oil companies often use sedimentation tanks or settling vessels to treat drilling and oil production wastewater, removing the suspended solid substances from it. Petroleum wastewater treatment: The secondary sedimentation tank is an essential structure in the biological treatment process, and it is widely used in the wastewater treatment facilities of petrochemical enterprises. It is primarily used to remove the sludge generated during the biological treatment process, thereby obtaining clarified treated water, while also providing the biological treatment equipment with a certain concentration of return sludge. 1. The suspension method, also known as the air flotation method, operates on the principle of introducing or generating a large number of bubbles into water, thereby creating a heterogeneous system consisting of water, air, and the substance to be removed. Under the influence of interfacial tension, the buoyancy of the bubbles, and the difference in hydrostatic pressure, the combination of bubbles and the substance to be removed rises to the surface, allowing it to be separated from the water. The air flotation method is generally used in the petroleum and petrochemical industries to remove oil from water. Using flotation agents is the simplest and most economical way to improve flotation efficiency. Initially, some inorganic flocculants such as AL2(SO4)3, basic ALCL3, and alum were used as flotation agents; later on, they were gradually replaced by polymer-based flotation agents such as polyaluminum chloride, polyacrylamide, and starch. 2. Oil separation: Oil separation is primarily used to remove suspended and coarsely dispersed oils from oily wastewater; therefore, it is widely applied in the petrochemical industry, especially where oil separation devices are used as key equipment in the treatment of oil extraction wastewater. Oil separation devices are generally divided into three types: plug flow type, inclined plate type, and combined plug flow-inclined plate type. Oil-containing wastewater is generally treated using oil separation tanks, while petrochemical wastewater is treated with oil separation ponds. The production of petroleum cracking catalysts primarily uses molecular sieve products as raw materials, which are then combined with kaolin, diaspore, ammonium salts, etc. Through processes such as gel formation, drying, and calcination, the catalysts are finally produced (Guo Hongshan, 2001). The wastewater generated during this production process has a complex composition, containing large amounts of ammonia nitrogen, suspended solids, Cl-, metal ions, and recalcitrant organic substances such as volatile phenols. Traditional aerobic biological treatment methods suffer from issues such as low volumetric load, high energy consumption, significant alkali consumption, and high operating costs. The emergence of new biological nitrogen removal technologies offers hope for solving these traditional problems.

The CANON process is a novel biological nitrogen removal technique. Its principle of nitrogen removal involves ammonia-oxidizing bacteria that use dissolved oxygen to oxidize NH4+-N into NO2--N, while anaerobic ammonia-oxidizing bacteria utilize the substrate provided by AOBs and the anaerobic environment they create to convert NH4+-N and NO2--N, thereby achieving nitrogen removal. The reaction process is as follows:

Since both AOBs and ANAMMOX are autotrophic bacteria, compared to traditional nitrogen removal processes, the CANON process can reduce aeration requirements by 63% and external carbon source usage by nearly 100%, making it one of the most promising biological nitrogen removal techniques. At present, research on the application of the CANON process is still in the experimental stage, and it is mainly used for treating wastewater with low C/N ratios such as sludge digestate and landfill leachate. There are few studies on wastewater from petroleum cracking catalysts.

The characteristics of wastewater from petroleum cracking catalysts—low C/N ratio, high water temperature, and high ammonia nitrogen levels—make it suitable for the application of the CANON process. However, the organic substances present in this wastewater can have an adverse effect on anaerobic ammonia oxidation. Electrocoagulation can be used as a pretreatment step for wastewater, allowing for the removal of suspended solids and some organic substances through processes such as flocculation, air flotation, and redox reactions. Therefore, this study employs electrocoagulation to pre-treat the wastewater before examining the initiation mechanism of the CANON process as well as its efficiency in removing organic substances and nitrogen, with the aim of providing insights for the nitrogen removal of wastewater from petroleum cracking catalysts and the broader application of the CANON process.

3. Coalescing oil recovery technology takes advantage of the differences in the properties of oil and water, as well as the significant variations in the affinity between oil particles and the surface of coalescing materials. When oily wastewater passes through a bed filled with such materials, oil particles are captured and retained on the surface and within the pores of the materials. As more oil particles accumulate, an oil film is formed. Once this oil film reaches a certain thickness, it coalesces into larger oil droplets that can then be separated from the water. Coalescing oil removal has become an important technology for treating petroleum wastewater. 4. Air lifting: The acidic water discharged from the production units in refineries contains mainly NH3, H2S, and CO2. If this water is discharged directly into the refinery’s wastewater treatment plant and treated using the conventional three-step process (oil separation, flotation, aeration), the resulting wastewater does not meet the discharge standards. To ensure the stable operation of the wastewater treatment plant and the compliance of the discharged water, wastewater with high levels of sulfur and ammonia nitrogen must undergo pretreatment in specialized equipment. By using the air lift method, with appropriate processes and operating conditions, wastewater can be purified to meet various requirements for reclaimed water quality or to satisfy the inlet water quality standards for wastewater treatment plants; moreover, by-products such as H2S and NH3 can be obtained as required. 5. Filtration is a process in which granular filter media with pores, such as quartz sand and anthracite filter media, are used to trap impurities in water, thereby clarifying the water. 6. Fractionation: It is a method for separating components within a mixture; in addition to distillation, fractionation can also be used to treat oily wastewater. The pressure transmitter industry is bound to become more sophisticated in the future. Some leading brands will continue to enhance the competitiveness of their products, improve the accompanying services, and accelerate the development of value-added products for transmitters in order to expand their product ranges. They will stop focusing on single types of products and instead add functional enhancements that facilitate daily use by customers, thereby driving a significant improvement in the technical standards of the entire industry and enabling pressure transmitters to truly evolve along technological lines.