Abstract: Printing and dyeing wastewater has the characteristics of large amount of water, high concentration of organic pollutants, deep color, large alkalinity, poor biodegradability, large changes of water quality and complex composition. It is one of the most difficult industrial wastewater. The purpose of this paper is to introduce the status quo of the development of domestic and foreign printing and dyeing wastewater treatment technologies. The methods of physical, chemical, physical and biological methods are introduced in detail. The applicable conditions and treatment effects of various treatment methods are listed, and their respective advantages and disadvantages . Keywords; printing and dyeing wastewater; treatment technology; research status quo Dyeing and printing industry is a major polluter in industry, printing and dyeing wastewater is the main textile and dyeing industry emissions. According to incomplete statistics, the discharge of domestic printing and dyeing wastewater is about 3 × 106-4 × 106m3 / d, accounting for about 35% of the total industrial wastewater. According to statistics, the total output of printed and dyed fabrics with statistical data in China is 2.9 × 10 10 m in 2003 with the statistics of small-scale printing and dyeing factories. The total production volume of total printed fabrics is estimated to be 3.2 × 10 10 m. The national annual printing and dyeing wastewater generated about 1.6 × 109t. Strengthening the treatment of printing and dyeing wastewater plays an important role in protecting the environment and maintaining the ecological balance. Printing and dyeing wastewater is the collective name of various waste water discharged in the process of printing and dyeing enterprises. Due to different fabric printing and dyeing process, the color and pollutant contained in printing and dyeing wastewater and the pH value required in printing and dyeing process are different. The printing and dyeing wastewater has the characteristics of large chroma, high organic content, large variation of water temperature, water quantity, water quality and pH value And other characteristics of wastewater treatment difficult. In recent years, with the use of a large number of new additives and slurries, the biodegradability of organic pollutants is reduced, making it more difficult to handle. 1. Dyeing wastewater discharge status and characteristics The discharge of printing and dyeing wastewater accounts for about 1/10 of the total discharge of industrial wastewater. Each year, about 6 × 108 ~ 7 × 108t of printing and dyeing wastewater is discharged into the water environment. Printing and dyeing wastewater is one of the main water pollution sources at present, The sustainable development of the industry, we must first solve the pollution of the printing and dyeing industry. Dyeing wastewater is characterized by complex composition, high organic content, high chroma, high CODcr, relatively low BOD5, poor biodegradability, large emissions and complex components. Besides Containing additives and a large number of slurry, the wastewater also contains aniline, nitrobenzene, phthalates containing benzene ring, amine, azo and other groups of toxic organic pollutants, not only difficult to biodegradable, and Mostly carcinogenic substances, endangering human health. 2. Printing and dyeing wastewater treatment methods commonly used (1) physical and chemical methods ①coagulation Chemical coagulation is a commonly used method of treating printing and dyeing wastewater and has been considered as one of the most effective and economical decolorization technologies. Coagulation is the coagulant dissociation and hydrolysis products under the action of the colloidal contaminants in water and fine suspended solids destabilization and coalescence into a separable flocs of the process, including the two processes of aggregation and flocculation, collectively For coagulation. Add coagulant in wastewater can achieve the purpose of reducing or eliminating the zeta potential so as to reduce or eliminate the repulsive energy peak between the colloidal particles and collide with the colloidal particles. Affect the coagulation effect of printing and dyeing wastewater, the main factors are water temperature, pH and dye varieties. Printing and dyeing wastewater temperature is generally relatively high, can accelerate the hydrolysis of inorganic salt coagulant process, the coagulation process is beneficial. The pH can be adjusted manually. Therefore, the dye species has become the main factor affecting the coagulation effect, but also the main basis for the choice of coagulant. How to choose efficient coagulant and effective coagulation process is the key of this technology. The main advantages of coagulation method is a one-time investment is low; operation and management of technical requirements is not high; for different water quality selection of appropriate flocculant, the treatment effect and treatment costs can be controlled at the appropriate level. Disadvantages: for some wastewater, there may be a large dosage or flocculant expensive situation, resulting in high operating costs and narrow scope of application of soluble colored pollutant bleaching poor results; produce a large number of chemical sludge, the sludge Processing and disposal further increase the operating costs and operational management of the difficulty, and easily lead to secondary pollution; covers a larger area. ② adsorption Adsorption is the use of adsorbent adsorption of water pollutants, can remove color, suspended solids, colloids and dissolved organic matter. In the printing and dyeing wastewater treatment used in the main adsorbent activated carbon, coke, silicon polymer, diatomaceous earth, kaolin and industrial slag. Different adsorbents are selective for dyes, affecting the conditions of adsorption temperature T, contact time t and pH value. It has been reported that the use of sawdust by weak acid hydrolysis after coking made of adsorbent, can be used to deal with a variety of wastewater [4]. Its advantages are: no need to dosing any agent, no sludge. Disadvantages: adsorbent easy to saturation, the treatment effect decreases with time; adsorbent regeneration or replacement is more cumbersome, higher cost, renewable waste and saturated waste sorbent easily lead to secondary pollution. The development of efficient and cheap adsorbent is the research direction of adsorption. (2) chemical methods ①oxidation method Unsaturated double bonds of chromophore groups in dye molecules can be oxidized and broken to form organic compounds or inorganic compounds with smaller molecular weight, so that the dyes lose their color-producing ability. The oxidation methods include chemical oxidation, photocatalytic oxidation and ultrasonic oxidation. Although the specific process is different, but the decolorization mechanism is the same. Chemical oxidation is the more mature research methods, the oxidant commonly used Fenton reagent (Fe2 + -H2O2) ozone, chlorine, sodium hypochlorite and so on. Photocatalytic oxidation is the use of certain substances (such as iron complexes, simple compounds, etc.) under the action of ultraviolet light to produce free radicals, the use of this highly active hydroxyl radicals can be involved in accelerating the oxidation-reduction reaction can be oxidized Including bio-oxidation is difficult to degrade all kinds of organic pollutants and make it completely inorganic. Dyeing wastewater decolorization is to allow oxidants to absorb light and generate strong oxidative free radicals to induce destruction of dye molecules chromophores, so as to achieve the purpose of decolorization degradation. TiO2 photocatalytic oxidation at pH = 3 ~ 11 produce O and? OH, the dye molecules quickly decomposed and get a good decolorization effect. The decolorization effect of the law is good, does not produce large amounts of sludge, good bactericidal effect, often lower operating costs, but one-time high investment, installation difficulties. In short, the oxidation method is an excellent decolorization method of printing and dyeing wastewater, but if the degree of oxidation is insufficient, although the chromophore groups of the dye molecules may be destroyed and decolorized, the COD in them is still not completely eliminated; if the dye molecules are fully oxidized, Energy, medicine consumption may be excessive, the cost is too high. ② electrochemical method Electrolysis is a very effective technology for the treatment of printing and dyeing wastewater, through the electrode reaction to make printing and dyeing wastewater purification. Its mechanism is the use of electrolytic oxidation, electrolytic reduction, electrolytic flocculation or electrolytic flotation and other effects destroy the molecular structure or the existence of decolorization. Its main advantages are: ①OH generated during the process of selective reaction directly with the dye in the wastewater, its degradation into carbon dioxide, water and simple organic matter, with little or no pollution; ② chemical processes generally at room temperature and pressure Can be carried out, high energy efficiency; ③ either alone, but also with other treatment methods combined, such as as a pre-treatment, can improve the biodegradability of wastewater. Therefore, electrolytic water treatment technology at home and abroad is called "environmentally friendly" technology. However, due to high energy consumption and high costs have not been valued. With the development of electrochemistry and power industry, the advent of various high efficiency reactors has led to a substantial reduction in the cost of treatment. Electrochemical methods have re-attracted people's attention, and further improve the catalytic performance of electrode materials, improve the current efficiency and reduce the electrode polarization In order to reduce energy consumption is still the main direction of the future. Laser Cutting Machine,Laser Cutter,Cnc Laser Cutter,Cnc Laser Cutting Machine Nantong Fengli Machine Tool CO.,LTD , https://www.jsfltech.com