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2018-01-18

Brief introduction of sewage treatment methods in chemical plant


1. chemical method treatment
 
 
 
Chemical methods use the chemical reaction to remove the organic and inorganic impurities in the water. Mainly chemical coagulation, chemical oxidation, electrochemical oxidation and so on. Chemical coagulation is mainly composed of tiny suspended solids and colloidal substances in water. By coagulating and flocculating chemicals, colloidal destabilization and precipitation can be removed. Coagulation can not only remove fine suspended particles with a particle size of 1O to 10mm in the wastewater, but also remove the chromaticity, microorganism and organic matter. The method is influenced by pH value, water temperature, water quality and water volume. It has low removal rate for some soluble organic and inorganic substances. Chemical oxidation is usually used to remove organic pollutants from chemical wastewater by oxidant. After chemical oxidation and reduction, wastewater can transform organic and inorganic toxic substances into non-toxic or less toxic substances, so as to achieve the purpose of wastewater purification. Commonly used are air oxidation, chlorination and ozonation. Because of its low oxidation capacity, air oxidation is mainly used for the treatment of wastewater containing strong reducing substances. Cl is commonly used oxidant, mainly used in the treatment of organic wastewater containing phenol and cyanide. Ozone treatment of wastewater has strong oxidation capacity and no two time pollution. Ozone oxidation, chlorine oxidation, the water treatment effect is good, but the high energy consumption, high cost, not suitable for the treatment of water and relatively low concentrations of chemical wastewater; electrochemical oxidation in the electrolytic cell, the organic pollutants in wastewater on the electrode due to the oxidation and reduction of pollutants in wastewater removal, the loss of electrons by oxidation at the anode cell, water Cl-, OH- is also available in the anode discharge generated Cl2 and oxygen indirectly oxidative damage of pollutants. In fact, in order to strengthen the role of the anodic oxidation, reduce internal resistance of the electrolytic bath, often add some sodium chloride in the wastewater of electrolytic cell, the so-called electric chloride, after adding NaCl can generate chlorine and hypochlorite in the anode, inorganic and organic matter in water also has strong effect of oxygen. In recent years, some new electrode materials have been found in electro oxidation and electroreduction, and some achievements have been achieved. However, there are still many problems, such as high energy consumption, high cost and side effects.
 
 
 
2. physical processing method
 
 
 
The physical methods commonly used in chemical wastewater include filtration, gravity precipitation and air floatation. The filtering method is based on the granular aggregate layer has a hole for intercepting water impurities, mainly suspended solids to reduce water, in the treatment of chemical wastewater filtration, pull box commonly used filter and microporous filter, microporous tube made of polyethylene, the pore size can be adjusted, more convenient; gravity precipitation method is the use of suspended particles can be precipitated the performance, the natural sedimentation in the role of gravity, in order to achieve a process of solid-liquid separation; flotation is generated by adsorption of tiny bubbles wrapped carrying suspended particles and carry out water method. The three physical methods are simple in process and convenient in management, but can not be applied to the removal of soluble waste water, which has great limitations.
 
 
 
3. photocatalytic oxidation technology
 
 
 
The photocatalytic oxidation technology combines O2, H2O2 and other oxidants with light radiation. The light is mainly ultraviolet light, including uv-H2O2, uv-O2 and so on. It can be used to treat the refractory substances such as CHCl3, CCl4, polychlorinated biphenyl and so on in sewage. In addition, there is synergetic effect between ultraviolet and iron ions in the ultraviolet Feton system. The rate of H2O2 decomposition to produce hydroxyl radicals is greatly accelerated, and the oxidation of organic matters is promoted.
 
 
 
The so-called photochemical reaction is the chemical reaction that can be carried out only under the action of light. In this reaction, the absorptive light energy of the molecule is excited to the high energy state, and then the electron excited state molecules are chemically reacted. The activation energy of the photochemical reaction comes from the energy of the photon. In the use of solar energy, photoelectric conversion and photochemical conversion have been a very active field of photochemical research. In the early 80s, photochemistry was applied to environmental protection, especially photochemical degradation and pollution control, including photochemical degradation without catalyst and catalyst. The former mostly uses ozone and hydrogen peroxide as oxidants, and then decomposes pollutants under ultraviolet light. The latter is also called photocatalytic degradation, which can be generally divided into two types: homogeneous and heterogeneous. Homogeneous photocatalytic degradation mainly Fe2 + or Fe3 + and H2O2 as the medium, the photo - Fenton (photo Fenton) reaction of the pollutants degradation, such reactions can directly use visible light; heterogeneous photocatalytic degradation is the pollution in the system of adding a certain amount of photosensitive semiconductor materials, optical radiation combined with a certain the energy, the electrons and holes of the photosensitive semiconductor excitation in light irradiation, adsorption in semiconductor on dissolved oxygen and water molecules and electron and hole, the generation of OH and other strong oxidizing free radicals, the contaminant between hydroxyl adduct, substitution and electron transfer. All or nearly all mineral pollutants, generating CO2, H2O and other ions such as NO3,
 
 
 
4. ultrasonic technology
 
 
 
Ultrasonic technology is to degrade and separate organic matter by controlling the frequency of ultrasonic and saturated gas.
 
 
 
The cavitation effect of power ultrasound provides a unique physical and chemical environment for the degradation of harmful organic matter in water, which leads to the realization of the purpose of ultrasonic sewage treatment. The high energy produced by the collapse of the ultrasonic cavitation bubble is enough to break the chemical bonds. In aqueous solution, the cavitation bubble collapsing to produce hydroxyl radicals and hydrogen radical oxidation reaction with organic matter. The unique physics of cavitation