Common treatment technologies of industrial wastewater
1、 Industrial wastewater treatment technology
1. Membrane technology
Membrane separation methods are commonly used in microfiltration, nanofiltration, ultrafiltration and reverse osmosis. Because membrane technology does not introduce other impurities in the treatment process and can realize the separation of macromolecular and small molecular substances, it is often used for the recovery of various macromolecular raw materials, such as the recovery of polyvinyl alcohol slurry from printing and dyeing wastewater by ultrafiltration technology.
2. Iron carbon micro electrolysis treatment technology
Iron carbon micro electrolysis is a good process for wastewater treatment based on the reaction principle of Fe / C primary battery, which is also known as internal electrolysis method, iron filings filtration method and so on. Iron carbon micro electrolysis is a comprehensive effect of electrochemical redox, electrochemistry on the electric enrichment of flocs, the coagulation of electrochemical reaction products, the adsorption of new flocs and bed filtration, mainly redox, electric adsorption and coagulation.
3. Ozone oxidation
Ozone is a kind of strong oxidant, which can react with reduced pollutants quickly, is easy to use and does not produce secondary pollution. It can be used for disinfection, color removal, deodorization, organic matter removal and COD reduction of sewage.
4. Magnetic separation technology
Magnetic separation technology is a new type of water treatment technology developed in recent years, which uses the magnetism of impurity particles in wastewater to separate. For non-magnetic or weakly magnetic particles in water, magnetic inoculation technology can make them magnetic. There are three methods of magnetic separation technology applied to wastewater treatment: direct magnetic separation, indirect magnetic separation and microbial magnetic separation.
5. SCWO (supercritical water oxidation) technology
SCWO uses supercritical water as the medium to oxidize and decompose organic matter in homogeneous phase. Organic pollutants can be decomposed into small inorganic molecules such as CO2 and H2O in a short time, and sulfur, phosphorus and nitrogen atoms can be transformed into sulfate, phosphate, nitrate and nitrite ions or nitrogen respectively. The United States lists SCWO as the most promising waste treatment technology in the field of energy and environment.
6. Fenton and Fenton like oxidation
The typical Fenton reagent is produced by the decomposition of H2O2 catalyzed by Fe2? Oh, thus initiating the oxidative degradation reaction of organic matter. Because the Fenton process takes a long time to treat wastewater and uses a large amount of reagents, and excessive Fe2 will increase the COD in the treated wastewater and produce secondary pollution.
Fenton method has mild reaction conditions, simple equipment and wide application range; It can be used as a separate treatment technology or combined with other methods, such as coagulation sedimentation method, activated carbon method and biological treatment method, as a pretreatment or advanced treatment method of refractory organic wastewater.
7. Electrochemical (catalytic) oxidation
Electrochemical (catalytic) oxidation technology directly degrades organic matter through anodic reaction, or degrades organic matter through oxidants such as hydroxyl radical (? Oh) and ozone. Electrochemical (catalytic) oxidation includes one-dimensional, two-dimensional and three-dimensional electrode systems. Due to the micro electric field electrolysis of three-dimensional electrode system, it is highly respected at present. Three dimensional electrode can be used to treat domestic sewage, pesticide, dye, pharmaceutical, phenol containing wastewater and other refractory organic wastewater, metal ions, landfill leachate and so on
8. Wet (catalytic) oxidation
Wet (catalytic) oxidation method uses O2 or air as oxidant (add catalyst) under the action of high temperature (150 ~ 350 ℃), high pressure (0.5 ~ 20MPa) and catalyst to (catalyze) oxidize dissolved or suspended organic matter or reduced inorganic matter in water, so as to achieve the purpose of removing pollutants. Wet air (catalytic) oxidation can be applied to the treatment of municipal sludge, industrial wastewater such as acrylonitrile, coking, printing and dyeing, and pesticide wastewater containing phenol, chlorohydrocarbon, organic phosphorus and organic sulfur compounds
9. Ultrasonic oxidation
Ultrasonic irradiation of organic pollutants in water with a frequency of 15 ~ 1000khz is a physicochemical process caused by cavitation effect. Ultrasound can not only improve the reaction conditions, speed up the reaction speed and improve the reaction yield, but also realize some difficult chemical reactions.
It integrates the characteristics of various water treatment technologies such as advanced oxidation, incineration and supercritical oxidation. In addition, it has simple operation and low requirements for equipment. It is of great significance in sewage treatment, especially in degrading organic pollutants with high toxicity and difficult degradation, accelerating the degradation rate of organic pollutants, realizing the harmless of industrial wastewater pollutants and avoiding the impact of secondary pollution.
2、 Treatment methods of different types of industrial wastewater
1. Chemical industry wastewater
Chemical industry wastewater mainly comes from production wastewater discharged from petrochemical industry, coal chemical industry, acid-base industry, chemical fertilizer industry, plastic industry, pharmaceutical industry, dye industry, rubber industry, etc.
The main measures for the prevention and control of chemical wastewater pollution are as follows: firstly, we should reform the production process and equipment, reduce pollutants, prevent the discharge of wastewater, and carry out comprehensive utilization and recovery; The treatment degree of wastewater that must be discharged shall be selected according to the water quality and requirements.
Primary treatment mainly separates suspended solids, colloids, oil slick or heavy oil in water. Water quality and quantity regulation, natural sedimentation, floating and oil separation can be adopted.
The secondary treatment is mainly to remove the biodegradable organic solutes and some colloids, and reduce the biochemical oxygen demand and some chemical oxygen demand in the wastewater. It is usually treated by biological method. After biological treatment, a considerable amount of COD remains in the wastewater, sometimes with high color, smell and taste, or due to the high requirements of environmental sanitation standards, the three-stage treatment method needs to be used for further purification.
The tertiary treatment is mainly to remove the organic pollutants and dissolved inorganic pollutants that are difficult to be biodegraded in the wastewater. The commonly used methods include activated carbon adsorption method and ozone oxidation method, as well as ion exchange and membrane separation technology. Various chemical industrial wastewater can be treated with different methods according to different water quality, quantity and the requirements of discharged water quality after treatment.
2. Printing and dyeing industrial wastewater
The printing and dyeing industry consumes a lot of water, usually 100-200t per 1t of textile Among them, 80% - 90% are discharged by printing and dyeing wastewater. Common treatment methods include recycling and harmless treatment.
recycling:
The wastewater can be recycled according to the characteristics of water quality, such as the diversion of bleaching and refining wastewater and dyeing and printing wastewater. The former can be washed by convection (I) multi use of water to reduce emissions;
Alkali liquor is usually recovered by evaporation. If the amount of alkali liquor is large, it can be recovered by three-way evaporation. If the amount of alkali liquor is small, it can be recovered by thin film evaporation;
Dye recovery For example, Shilin dye can be acidified into cryptobenzoic acid as colloidal particles It is suspended in the residual liquid and recycled after sedimentation and filtration.
Harmless treatment can be divided into:
Physical treatment methods include precipitation method and adsorption method. Sedimentation method mainly removes suspended solids in wastewater; Adsorption method is mainly to remove dissolved pollutants and decolorization in wastewater.
Chemical treatment methods include neutralization, coagulation and oxidation. Neutralization method is to adjust the pH in wastewater and reduce the chromaticity of wastewater; Coagulation method is to remove disperse dyes and colloidal substances from wastewater; Oxidation method is to oxidize reducing substances in wastewater and precipitate sulfide dyes and vat dyes.
Biological treatment methods include activated sludge, biological rotary table, biological rotary drum and biological contact oxidation. In order to improve the effluent quality and meet the discharge standard or recovery requirements It is often necessary to adopt several methods for joint treatment.
3. Paper industry wastewater
Papermaking wastewater mainly comes from the two production processes of pulping and papermaking in the production of papermaking industry. Pulping is to separate the fibers from plant raw materials, make pulp, and then bleach; Papermaking is to dilute, shape, press and dry the slurry to make paper. Both processes discharge a large amount of wastewater.
The wastewater from pulping is the most polluted. The wastewater discharged during pulp washing is dark brown, which is called black water. The concentration of pollutants in black water is very high, BOD is as high as 5-40g / L, and contains a large amount of fiber, inorganic salt and pigment. The wastewater discharged from bleaching process also contains a lot of acid and alkali substances. The waste water discharged from the paper machine is called white water, which contains a large amount of fiber and filler and rubber added in the production process.
The treatment of wastewater from papermaking industry should focus on improving the rate of circulating water and reducing water consumption and wastewater discharge. At the same time, we should also actively explore various reliable, economic and effective treatment methods that can make full use of useful resources in wastewater. For example, the flotation method can recover the fibrous solid matter in white water, the recovery rate can reach 95%, and the clarified water can be reused; The combustion method can recover sodium hydroxide, sodium sulfide, sodium sulfate and other sodium salts combined with organic matter in black water.