What are the deep treatment processes of sewage treatment

This refers to the city sewage or industrial wastewater after primary and secondary treatment, in order to achieve a certain standard of reuse of sewage as a water resource back to the production or life of the further water treatment process.

For sewage (wastewater) raw water quality and water quality requirements after treatment can be further used in three-stage treatment or multi-stage treatment process. Commonly used in the removal of trace COD and BOD organic pollutants in water, SS and nitrogen, phosphorus and high concentrations of nutrients and salts.

Treatment methods

Depth treatment methods are:

Flocculation and precipitation method, sand filtration, activated carbon method, ozone oxidation, membrane separation, ion exchange, electrolysis, wet oxidation, evaporation and concentration of physicochemical methods such as biological denitrification, dephosphorization method. Deep treatment methods are expensive, more complex management, in addition to the cost per ton of water is about 4-5 times more than the cost of primary treatment.

Methods

1, activated carbon adsorption method activated carbon is a kind of porous material, and easy to automatically control, water quantity, water quality, water temperature changes adaptability, so activated carbon adsorption method is a sewage depth treatment technology with broad application prospects. Activated carbon has a very obvious removal effect on organic matter with molecular weight of 500~3,000, and the removal rate is generally 70%~86.7%, which can economically and effectively remove smell, color, heavy metal, disinfection by-products, chlorinated organic matter, pesticide, radioactive organic matter, etc. The commonly used activated carbon is powdered carbon, which is mainly used in the treatment of sewage. Commonly used activated carbon is mainly powdered activated carbon (PAC), granular activated carbon (GAC) and biological activated carbon (BAC) three categories. In recent years, more foreign research on PAC has been deepened to the study of the adsorption capacity of various specific pollutants. Asia-Pacific Water Treatment (Tianchang) Co., Ltd. according to the degree of water pollution in the water treatment system, adding powdered activated carbon to remove COD in water, filtered water color can be reduced to the bottom of 1 to 2 degrees; odor reduced to 0 degrees. GAC is used more in foreign water treatment, the treatment effect is more stable, the U.S. Environmental Protection Agency (USEPA) drinking water standards of the 64 indicators of organic matter, 51 will be GAC GAC listed as the most effective technology. The disadvantage of GAC treatment process is that the infrastructure and operating costs are high, and easy to produce carcinogens such as nitrites, and poor adaptability to sudden pollution. How to further reduce the capital investment and operating costs, and reduce the cost of activated carbon regeneration will become the focus of future research.BAC can play a synergistic role in biochemical and physical and chemical treatments, thus prolonging the working cycle of activated carbon, greatly improving the treatment efficiency, and improving the quality of the effluent water. The shortcomings are that the activated carbon micropore is easy to be blocked, the pH range of the influent water is narrow, and the shock load is poor, etc. At present, the BAC technology is applied in Europe. At present, the application of BAC technology in Europe has developed to more than 70 water plants, the most widely used is the depth treatment of water. Fushun Petrochemical Branch Petroleum Plant No. 3 adopts BAC technology, which not only saves the replenishment of fresh water, reduces the amount of sewage discharge, alleviates the pollution of water bodies, reduces the production cost, but also reflects the unity of economic and social benefits. The focus of future research is to reduce investment costs and increase a variety of pretreatment measures in conjunction with BAC to improve the treatment effect.

2, membrane separation method membrane separation technology is a new type of polymer separation membrane as a representative of the fluid separation unit operation technology. Its most important feature is that the separation process is not accompanied by phase changes, only by a certain pressure as the driving force can obtain a high separation effect, is a very energy-saving separation technology. Microfiltration can remove bacteria, viruses and parasitic organisms, etc. It can also reduce the phosphate content in water. The Tianjin Development Area Wastewater Treatment Plant uses microfiltration membranes for the deep treatment of SBR secondary effluent, which meets the needs of municipal miscellaneous uses such as landscaping, road washing and toilet flushing, as well as the needs of domestic miscellaneous uses. Ultrafiltration is used to remove macromolecules, and the removal rate of COD and BOD of the secondary effluent is more than 50%. Beijing Gaobeidian Wastewater Treatment Plant adopts ultrafiltration for deep treatment of secondary effluent, the quality of produced water meets the standard of domestic miscellaneous water, and the reused effluent is used for car washing, which saves 4,700 m3 of water per year. reverse osmosis is used to reduce the degree of mineralization and remove the total dissolved solids, and the desalination rate of the secondary effluent reaches more than 90%, the removal rate of COD and BOD is around 85%, and the bacterial removal rate is more than 90%. A power plant in Myanmar uses reverse osmosis membrane and electro desalination combined technology for boiler make-up water. The water treated by reverse osmosis removes most of the inorganic salts, organic matter and microorganisms. Nanofiltration between reverse osmosis and ultrafiltration, its operating pressure is usually 0.5 ~ 1.0 MPa, a significant feature of the nanofiltration membrane is ion-selective, which removes divalent ions up to 95% or more, and monovalent ions with a lower removal rate of 40% to 80%. The use of membrane bioreactor - nanofiltration membrane integrated technology for the treatment of molasses alcohol wastewater has achieved better results, the effluent COD is less than 100 mg / L, the wastewater reuse rate is greater than 80%. There is still a big gap between the application of membrane technology in the field of deep treatment in China and the advanced level in the world. Future research focus on the development and manufacture of high-strength, long-life, anti-pollution, high-flux membrane materials, focusing on solving the membrane contamination, concentration polarization and cleaning and other key issues.

3, advanced oxidation method of industrial production of high concentrations of organic pollutants and toxic pollutants emitted, a variety of hazardous, some pollutants are difficult to biodegradation and biochemical reactions have inhibited and toxic effects. The advanced oxidation method in the reaction to produce highly active free radicals (such as ?OH, etc.), so that difficult to degrade organic pollutants into easily degradable small molecules, and even directly generate CO2 and H2O, to achieve the purpose of harmlessness.

3.1

Wet oxidation method Wet oxidation method (WAO) is at high temperature (150 ~ 350 ℃), high pressure (0.5 ~ 20 MPa) under the use of O2 or air as an oxidizing agent, oxidizing organic or inorganic substances in the water to achieve the purpose of removing the pollutants, and the end product is CO2 and H2O. 2002 the introduction of WAO

Process, completely solved the slag follow-up and malodor pollution problems, and low operating costs, high oxidation efficiency.

3.2 Wet catalytic oxidation method of wet catalytic oxidation (CWAO) is the traditional wet oxidation process by adding a suitable catalyst so that the oxidation reaction can be completed in milder conditions and shorter time, but also so as to reduce the corrosion of the equipment, reduce operating costs. At present, a set of continuous flow type CWAO industrial experimental device built in Kunming City, has demonstrated a better economy. The catalysts of wet catalytic oxidation method are generally divided into three categories: metal salt, oxide and compound oxide. At present, considering the economy, the most applied catalysts are transition metal oxides such as Cu, Fe, Ni, Co, Mn 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.