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Common deep sewage treatment methods

Release time: 2019/8/23 Click times: 3195

The so-called in-depth sewage treatment refers to a further water treatment process in which urban sewage or industrial wastewater is treated as a water resource for reuse in production or living after primary or secondary treatment. The common deep sewage treatment methods are as follows:

1 Activated carbon adsorption method Activated carbon is a porous substance, which is easy to automatically control, and has strong adaptability to changes in water volume, water quality, and water temperature. Therefore, activated carbon adsorption method is a wastewater advanced treatment technology with broad application prospects. Activated carbon has the obvious effect of removing organic matter with a molecular weight of 500 to 3000. The removal rate is generally 70% to 86.7%. It can economically and effectively remove odor, color, heavy metals, disinfection by-products, chlorinated organics, pesticides, and radioactive organics. Wait.
The commonly used activated carbons mainly include powder activated carbon (PAC), granular activated carbon (GAC) and biological activated carbon (BAC).
In recent years, there have been many researches on PAC abroad, and the research on the adsorption capacity of various specific pollutants has been in-depth. According to the degree of water pollution, Zibo Yinhuang Water Supply Co., Ltd. adds powdered activated carbon to the water treatment system to remove COD in the water. After filtering, the color of the water can be reduced by 1 to 2 degrees; the odor is reduced to 0 degrees.
GAC is widely used in foreign water treatment, and its treatment effect is relatively stable. Among the 64 organic matter indicators of the US Environmental Protection Agency (USEPA) drinking water standard, 51 of them have GAC as the most effective technology. Disadvantages of the GAC treatment process are high capital construction and operating costs, and easy production of carcinogens such as nitrite, and poor adaptability to sudden pollution. How to further reduce infrastructure investment and operating costs, and reduce the cost of activated carbon regeneration will become the focus of future research.
BAC can exert the synergistic effect of biochemical and physical and chemical treatments, thereby extending the working cycle of activated carbon, greatly improving the treatment efficiency, and improving the quality of the effluent water. The disadvantages are that the activated carbon micropores are easily blocked, the pH range of the incoming water is narrow, and the impact load is poor. At present, there are more than 70 water plants in Europe applying BAC technology, and the most widely used is the advanced treatment of water. Fushun Petrochemical Company's No. 3 Petroleum Plant uses BAC technology, which not only saves the replenishment of fresh water, reduces sewage discharge, reduces water pollution, reduces production costs, but also reflects the unification of economic and social benefits. Future research will focus on reducing investment costs and increasing the use of various pretreatment measures in combination with BAC to improve the treatment effect.
2 Membrane separation method Membrane separation technology is a new type of fluid separation unit operation technology represented by polymer separation membrane. Its biggest feature is that it does not accompany the phase change in the separation process. It can obtain a high separation effect by only a certain pressure as a driving force. It is a very energy-saving separation technology.
Microfiltration can remove bacteria, viruses and parasites, and it can also reduce the phosphate content in water. The Tianjin Development Zone Sewage Treatment Plant uses microfiltration membranes for advanced treatment of SBR secondary effluent, which meets the needs of municipal and household miscellaneous uses such as landscape, road surface flushing and toilet flushing.
Ultrafiltration is used to remove macromolecules, and the COD and BOD removal rate of secondary effluent is greater than 50%. Beijing Gaobeidian Sewage Treatment Plant uses ultrafiltration to further process the secondary effluent. The quality of the produced water reaches the standard of domestic miscellaneous water. The reused sewage is used for car washing, which can save 4700 m3 of water per year.
Reverse osmosis is used to reduce the degree of mineralization and remove total dissolved solids. The desalination rate of secondary effluent reaches over 90%, the removal rate of COD and BOD is about 85%, and the removal rate of bacteria is more than 90%. A power plant in Myanmar uses a combination of reverse osmosis membrane and electric desalination technology for boiler make-up water. The water treated by reverse osmosis can remove most of the inorganic salts, organic matter and microorganisms.
Nanofiltration is between reverse osmosis and ultrafiltration, and its operating pressure is usually 0.5 to 1.0 MPa. A significant feature of the nanofiltration membrane is its ion selectivity. Its removal rate of divalent ions is more than 95%. The removal rate of ions is low, ranging from 40% to 80%. Membrane bioreactor-nanofiltration membrane integrated technology has been used to treat molasses alcohol wastewater with good results. The effluent COD is less than 100 mg / L, and the wastewater reuse rate is greater than 80%.
The application of China's membrane technology in the field of advanced processing is still far from the world *. Future research will focus on the development and manufacture of high-strength, long-life, anti-pollution, and high-throughput membrane materials, focusing on solving key issues such as membrane pollution, concentration polarization, and cleaning.
3 The high-concentration organic pollutants and toxic and harmful pollutants emitted in the industrial production of advanced oxidation methods are of many types and harmful, and some pollutants are difficult to biodegrade and have inhibitory and toxic effects on biochemical reactions. The advanced oxidation method generates extremely active free radicals (such as OH, etc.) in the reaction, transforms difficult-to-degrade organic pollutants into easily-degradable small molecular substances, and even directly generates CO2 and H2O, thereby achieving the purpose of harmlessness.
3.1 Wet Oxidation Method Wet oxidation method (WAO) uses O2 or air as an oxidant at high temperature (150-350 ℃) and high pressure (0.5-20 MPa) to oxidize organic or inorganic substances in water to achieve the purpose of removing pollutants. The final products are CO2 and H2O [14]. Fujian Refining & Chemical Co., Ltd. introduced the WAO process in 2002, which completely solved the follow-up treatment of alkali residues and the problem of fouling pollution, and had low operating costs and high oxidation efficiency.
3.2 Wet Catalytic Oxidation Method Wet catalytic oxidation method (CWAO) is to add a suitable catalyst to the traditional wet oxidation process so that the oxidation reaction can be completed under milder conditions and in a shorter period of time, which can also reduce equipment corrosion, Reduce operating costs. At present, a set of continuous flow-type CWAO industrial experimental device built in Kunming has shown a good economy. The catalysts of the wet catalytic oxidation method are generally classified into three types: metal salts, oxides and composite oxides. At present, considering economy, the most widely used catalysts are transition metal oxides such as Cu, Fe, Ni, Co, Mn, etc. and their salts. The use of solid catalysts can also avoid the loss of catalysts, the generation of secondary pollution, and the waste of funds.
3.3 Supercritical water oxidation method The supercritical water oxidation method raises the temperature and pressure above the critical point of water, and the water in this state is called supercritical water. In this state, the density, dielectric constant, viscosity, diffusion coefficient, conductivity, and solvent chemistry of water are all different from ordinary water. The higher reaction temperature (400 ~ 600 ℃) and pressure also speed up the reaction rate, which can reach a high degree of damage to organic matter in a few seconds.

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