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Industrial wastewater treatment

2018-03-03 17:36:00

According to the chemical properties of the main pollutants, industrial wastewater is classified into: inorganic wastewater containing mainly inorganic pollutants, organic wastewater containing mainly organic pollutants, mixed wastewater containing organic and inorganic substances, heavy metal wastewater, wastewater containing radioactive substances and cooling water polluted only by heat. For example, electroplating wastewater and mineral processing wastewater is inorganic wastewater, food or petroleum processing wastewater is organic wastewater, printing and dyeing industry production process is mixed wastewater, different industries excluded wastewater contains different components. According to the characteristics of industrial wastewater treatment, we think that appropriate pretreatment methods should be adopted according to the actual water quality of wastewater, such as flocculation, internal electrolysis, electrolysis, adsorption, photocatalytic oxidation and other processes to destroy the refractory organic matter in sewage and improve the biodegradability of sewage. Then combined with biochemical methods, such as SBR, contact oxygen industrial technology, A/O process, to further treat industrial wastewater.


Industrial wastewater treatment 1 Activated carbon Activated carbon can be divided into powder and granular, is a special treatment of carbon, with countless small pores, huge surface area, per gram of activated carbon surface area of 500 ~ l 500 m. Powdered activated carbon has strong adsorption capacity, easy preparation and low price, but it is difficult to regenerate and generally can not be reused. Granular activated carbon is more expensive, but it can be reused after regeneration, and the working conditions are better when used, and the operation is convenient. Therefore, more granular activated carbon is used in water treatment. In industrial sewage treatment, activated carbon is mainly used to treat cyanide-containing sewage, methanol-containing sewage, phenol-containing sewage, mercury-containing sewage, chromium-containing sewage, etc.


High concentration of organic sewage has caused great damage to China's precious water, but the existing biological treatment methods are difficult to treat substances with poor biodegradability and relative molecular mass from thousands to tens of thousands, and Advanced Oxidation Process, Referred to as AOPs, it can directly mineralize or improve the biodegradability of pollutants through oxidation, and also has great advantages in the treatment of trace harmful chemicals such as environmental hormones, which can make most of the organic matter completely mineralized or decomposed, and has a good application prospect. Common advanced oxidation technologies include air wet oxidation, catalytic wet oxidation, critical water oxidation, photochemical oxidation and so on. Industrial wastewater treatment (1) Wet air oxidation method Wet air oxidation method is the air as an oxidizing agent, the dissolved substances in water (including inorganic substances and organic matter) through the oxidation reaction into harmless new substances, or into the form that is easily separated from the water (gas or solid), so as to achieve the purpose of treatment. Under normal circumstances, the solubility of oxygen in water is very low 1 atm, at 20℃, the solubility of oxygen in water is about 9 mg/L), so at normal temperature and pressure, this oxidation reaction is very slow, especially for high concentration of pollutants, the oxidation reaction using oxygen in the air is slower. Various auxiliary means are needed to promote the reaction (usually with the help of high temperature, high pressure and the role of catalysts). In general, under the conditions of 200-300 oC and 100-200 ATM, the solubility of oxygen in water will increase, and almost all pollutants can be oxidized into carbon dioxide and water. The key of wet air oxidation is to produce enough free radicals to supply the oxidation reaction. Although this method can degrade almost all organic matter, due to harsh reaction conditions, high requirements for equipment (to withstand high temperature and pressure), and large fuel consumption, it is not suitable for the treatment of large amounts of sewage. Industrial wastewater treatment (2) Catalytic Wet OxidationProcess Catalytic wet oxidation process (CWOP) is an advanced treatment method of industrial wastewater (a physicochemical method). It is based on the principle of catalytic combustion of organic matter in sewage under high temperature and high pressure to purify and treat high-concentration organic sewage. Its most significant feature is that hydroxyl free radical is the main oxidizing agent to react with organic matter, and the organic free radical generated in the reaction can continue to participate in the chain reaction of •OH. Or through the generation of organic peroxides free radicals after further oxidative decomposition reaction until degradation into the final products CO and H 0, so as to achieve the purpose of oxidative decomposition of organic matter. Industrial wastewater treatment (3) Supercritical water oxidation method Supercritical water oxidation technology benefits from the supercritical properties of water. At 374.3c [=] and 22 MPa, the physical properties of water, especially the solubility properties, are completely different from those at room temperature, and this state is called the supercritical state. In the supercritical state, water has a high ability to dissolve organic matter just like a mild gas, and can be completely miscible with light organic gases and CO, but inorganic compounds, especially salts, are difficult to dissolve in it. In addition, supercritical water has a higher diffusion coefficient and a lower viscosity. These supercritical properties, combined with high temperature and pressure, make water an ideal medium for the oxidation of organic matter, so that the REDOX reaction can be carried out completely in the homogeneous phase without interfacial mass transfer resistance, which is often the control step of wet oxidation method. Industrial wastewater treatment (4) Photochemical oxidation method Photochemical reaction is a chemical reaction under the action of light, using ozone or hydrogen peroxide as an oxidizing agent to oxidize and decompose pollutants under ultraviolet irradiation, so as to achieve sewage treatment. Photochemical oxidation systems mainly include UV/H 0 system, UV/O system, system and UV/O3 / H202 system J. Take uv/H2 O2 system as an example, this system is mainly used for the treatment of low-concentration sewage with a concentration of 10-6, but not for the treatment of high-intensity polluted sewage. It can completely harmless pollutants, and the removal capacity of organic matter is stronger than that of hydrogen peroxide or ultraviolet light alone, which is a more economical choice and can be assembled in different locations in a short time. However, it is not suitable for treating soil, because ultraviolet light can not penetrate soil particles. Light is easily blocked by precipitation, reducing the penetration rate of uV, so the pH value of sewage should be controlled in use to prevent the precipitation of metal salts in the oxidation process from blocking the penetration of light. The experimental study of the removal of trihalomethane from drinking water by this method shows that the total organic carbon content in drinking water can be reduced while the removal of trichloromethane, and the water quality can be further improved. The test of using uv/H 0 system to treat groundwater polluted by tetrahalomethane shows that the removal rate can reach 97.3% to 99%, and the cost is comparable to that of activated carbon treatment. In the UV/H 0 system, each molecule of H 0 can produce two molecules of hydroxyl, which can not only effectively remove organic pollutants in the water, but also will not cause secondary pollution, and no subsequent treatment is required.


In recent years, membrane technology has developed rapidly, and has been widely used in the fields of electric power, metallurgy, petroleum and petrochemical, medicine, food, municipal engineering, sewage reuse and seawater desalination, etc., and the demand for membrane technology and equipment for all kinds of projects has increased rapidly. At present, microfiltration, ultrafiltration, reverse osmosis, nanofiltration, dialysis, electrodialysis, gas separation, pervaporation, inorganic membrane and other technologies are widely used in petroleum, chemical, environmental protection, energy, electronics and other industries, and have produced obvious economic and social benefits, will play an important strategic role in the 21st century industrial technology transformation. At the same time, the high support and attention of the relevant departments of the national government has also brought unprecedented opportunities to the development of the film industry. The separation purpose of microfiltration is to remove particles from solution and gas, and to retain particles with a particle size of 0.02-10 m. It is the most common technology used in all membrane processes and has the largest total sales, mainly for filtration and bacterialization in the pharmaceutical industry and the preparation of high purity water. The separation purpose of ultrafiltration (including nanofiltration) is to remove large molecules from solution, remove small molecules from large molecular solution, and classify large molecules, and trap particles with a particle size of 1.0-20 nm. Ultrafiltration technology can be used to recover paint in electrophoretic paint wastewater and is now widely used in electrophoretic paint automation lines around the world. In Japan and other countries, the industrial waste liquid of papermaking has also been treated by ultrafiltration technology. In the mining and metallurgical industries, the application of ultrafiltration technology is becoming increasingly important, using this technology to treat acid mineral effluents, its permeable solution can be used in the ring, and the concentrated solution can recover useful substances. At the same time, the production of integrated circuits in the electronic industry and the water process in the pharmaceutical industry have also begun to widely use ultrafiltration technology. Nanofiltration is a new separation technology developed on the basis of reverse osmosis. In the aspect of sewage treatment, nanofiltration membrane is used to decolorize the waste liquid formed in the extraction stage of wood pulping alkali, and the decolorization rate can reach more than 98%. Nanofiltration membrane can also be used to separate metal sulfate and nitrate from acidic solution, in which the retention rate of nickel sulfate can reach 95%.