The printing and dyeing industry is a major industrial wastewater discharge. According to incomplete statistics, the daily discharge of printing and dyeing wastewater in the country is 3×10 6 to 4×10 6 m 3 . Printing and dyeing wastewater has the characteristics of large water volume, high organic pollutant content, deep color, large alkalinity and large water quality change. It is an industrial wastewater that is difficult to treat. In recent years, due to the development of chemical fiber fabrics, the rise of artificial silk and advances in finishing technology, PVA pulp, rayon alkaline hydrolysate (mainly phthalic acid), new additives and other difficult biodegradable organic compounds A large amount of printing and dyeing wastewater has increased its COD concentration from hundreds of mg/L to 2,000-3,000 mg/L, which has reduced the COD removal rate of the original biological treatment system from 70% to 50% or even lower. Traditional biological treatment processes have been seriously challenged; traditional chemical precipitation and air flotation methods have a COD removal rate of only about 30% for such printing and dyeing wastewater. Therefore, the development of economical and effective printing and dyeing wastewater treatment technology has increasingly become a topic of concern in today's environmental protection industry. 
1 Printing and dyeing wastewater source, water quality and water volume
1.1 Sources: Four processes in printing and dyeing process must discharge waste water. The pretreatment stage (including singeing, desizing, scouring, bleaching, mercerizing, etc.) should discharge desizing wastewater, scouring wastewater, bleaching wastewater and mercerized wastewater. The dyeing process discharges the dyeing wastewater, and the printing process discharges the printing waste water and the soap liquid waste water, and the finishing process discharges the finishing waste water. Printing and dyeing wastewater is a mixed wastewater of the above various types of wastewater, or a comprehensive wastewater other than bleaching wastewater. 
1.2 Water quality and quantity The water quality of printing and dyeing wastewater varies with the type of fiber used and the processing technology. The composition of pollutants varies greatly. Generally, the printing and dyeing wastewater has a pH of 6 to 10, a CODCr of 400 to 1 000 mg/L, a BOD5 of 100 to 400 mg/L, a SS of 100 to 200 mg/L, and a chromaticity of 100 to 400 times. However, when the printing and dyeing process and the types of fibers and processing techniques used are changed, the quality of wastewater will change greatly. For example, when the wastewater contains alkali-reduced waste water produced in the polyester silk screen printing and dyeing process, the COD Cr of the wastewater will increase to 2 000  to 3 000 mg/L, and the BOD5 will increase to 800 mg. Above /L, the pH value is 11.5 to 12, and the wastewater quality deteriorates with the increase in the amount of waste dyeing of the polyester silk screen dyeing alkali. When the amount of CODCr in the alkali-reduced wastewater added exceeds 20% of the amount of CODCr in the wastewater, the biochemical treatment will be difficult to adapt. The drainage situation in each process of printing and dyeing is generally:
(1) Desizing wastewater: The amount of water is small, but the concentration of pollutants is high, which contains various slurries, slurry decomposition products, lint, starch alkali and various additives. The wastewater is alkaline and has a pH of about 12. The sizing is mainly starch-based (such as cotton) desizing wastewater, which has high COD and BOD values ​​and good biodegradability; sizing is mainly based on polyvinyl alcohol (PVA) (such as polyester-cotton warp) desizing wastewater. C OD is high and BOD is low, and wastewater is less biodegradable. 
(2) Refracting wastewater: large amount of water, high concentration of pollutants, including cellulose, fruit acid, wax, oil, alkali, surfactant, nitrogenous compounds, etc., the wastewater is strong alkaline, high water temperature, brown . 
(3) Bleaching wastewater: The amount of water is large, but the pollution is light, and it contains residual bleaching agent, a small amount of acetic acid, oxalic acid, sodium thiosulfate and the like. 
(4) Mercerized wastewater: high alkali content, NaOH content is 3% to 5%. Most printing and dyeing plants use condensed concentration to recover NaOH. Therefore, mercerized wastewater is generally rarely discharged. After repeated use of the process, the final discharged wastewater is still strong. Alkaline, BOD, COD, SS are higher. 
(5) Dyeing wastewater: The water volume is large, and the water quality varies with the dye used. It contains slurry, dye, auxiliary agent, surfactant, etc. It is generally strong alkaline, high chroma, and COD is higher than BOD. More, less biodegradable. 
(6) Printing wastewater: The water volume is large. In addition to the wastewater in the printing process, it also includes soaping and washing wastewater after printing. The concentration of pollutants is high, including pulp, dyes, additives, etc., BOD and COD are compared. high. 
(7) Finishing wastewater: The amount of water is small, and it contains lint, resin, oil, slurry, and the like. 
(8) Alkali-reduced waste water: It is produced by the polyester silk alkali reduction process, mainly containing polyester hydrolysate terephthalic acid, ethylene glycol, etc., wherein the terephthalic acid content is as high as 75%. The alkali reduction wastewater not only has a high pH value (generally >12), but also has a high organic matter concentration. The CODCr in the wastewater discharged from the alkali reduction process can be as high as 90,000 mg/L, and the polymer organic matter and some dyes are difficult to be biodegraded. The wastewater is a high concentration of refractory organic wastewater. 
2 Printing and dyeing wastewater treatment method
At present, the domestic printing and dyeing wastewater treatment methods are mainly biochemical methods, and some chemical systems are also connected in series. This is basically the case in foreign countries. Due to the development of chemical fiber fabrics in recent years and the advancement of finishing technology after printing and dyeing, PVA pulp, new auxiliaries and other difficult biodegradable organic substances have entered the printing and dyeing wastewater in large quantities, which makes the processing more difficult. Most of the original biological treatment systems have dropped from the original 70% COD removal rate to about 50% or even lower. The removal of chromaticity is a major problem in the treatment of printing and dyeing wastewater, and the old biochemical method has been unsatisfactory in terms of discoloration. In addition, the COD caused by chemical pulp such as PVA accounts for a considerable proportion of the total COD of printing and dyeing wastewater, but its removal rate is only 20% to 30% because it is difficult to be utilized by ordinary microorganisms.
In response to the above problems, in recent years, some research work has been carried out at home and abroad, mainly on the exploration and application of new biological treatment processes and efficient specialized bacteria and new chemical agents. Representative of these are: anaerobic-aerobic biological treatment process, screening and application research of high-efficiency decolorizing bacteria and PVA degrading bacteria, and development of high-efficiency decolorizing coagulant. The following is a review of the three aspects of physical law, chemical method and biological method, and introduces the current methods and research status of printing and dyeing wastewater treatment. 
2.1 Physical method for printing and dyeing wastewater treatment--Adsorption method The most widely used physical treatment method is the adsorption method, which is to mix powder or granules of porous substances such as activated carbon and clay with waste water, or to let waste water pass through its granules. A filter bed consisting of adsorbing pollutants in the wastewater adsorbed on the surface of the porous material or removed by filtration. At present, foreign countries mainly adopt activated carbon adsorption method (mostly used for tertiary treatment), which is very effective for removing dissolved organic matter in water, but it can not remove colloid and hydrophobic dye in water, and it only applies to cationic dyes, direct dyes, Water-soluble dyes such as acid dyes and reactive dyes have good adsorption properties. According to Saito T. et al., the adsorption rate, BOD removal rate and COD removal rate of activated carbon are 93%, 92% and 63%, respectively. The adsorption capacity of activated carbon can reach 500mgCOD/g carbon. If the sewage is first aerated, Speed ​​up the adsorption rate. However, if the wastewater BOD5 is >200 mg / L, it is uneconomical to use this method.
The adsorbent used in the adsorption treatment is various, and the selectivity of the adsorbent to the dye should be considered in the project, and the adsorbent should be selected according to the quality of the wastewater. Studies have shown that in the printing wastewater of pH=12, using silicon polymer (methyl oxygen) as adsorbent, the removal rate of anionic dye can reach 95%-100%.
Kaolinite is also an adsorbent. Studies have shown that kaolin can effectively adsorb yellow direct dyes in wastewater by long-chain organic cation treatment. In addition, the domestic application of active diatomite and cinder to treat traditional printing and dyeing process wastewater, the cost is lower, the decolorization effect is better, the disadvantage is that the amount of sludge generated is large, and further processing is difficult. 
2.2 Chemical treatment of printing and dyeing wastewater
2.2.1 Coagulation method  There are mainly coagulation sedimentation method and coagulation air flotation method. Most of the coagulants used are mainly aluminum or iron salts, of which bridge adsorption by basic aluminum chloride (PAC) The performance is better, and the price of ferrous sulfate is the lowest. In recent years, the use of polymer coagulants has increased in foreign countries, and there is a tendency to replace inorganic coagulants. However, in the domestic market, the use of polymer coagulants is still rare. It has been reported that weak anionic polymer coagulants have the widest range of use, and if used in combination with aluminum sulfate, they can exert better effects. The main advantages of the coagulation method are simple process, convenient operation and management, low equipment investment, small floor space, high decolorization efficiency for hydrophobic dyes; disadvantages are high operating costs, large amount of sludge and difficulty in dehydration. Aqueous dyes have poor handling. 
2.2.2 Oxidation method Ozone oxidation method is widely used in foreign countries. Zima SV et al. summarized the mathematical model of ozone decolorization of printing and dyeing wastewater. Studies have shown that when the amount of ozone is 0.886gO3 / g dye, the decolorization rate of light brown dye wastewater is 80%; the study also found that the amount of ozone required for continuous operation is higher than the amount of ozone required for intermittent operation, and the separator is installed in the reactor. Can reduce the amount of ozone by 16.7%. Therefore, it is preferable to design a reactor which is intermittently operated by ozone oxidation decolorization, and it is conceivable to install a separator therein.
Ozone oxidation method can obtain good decolorization effect for most dyes, but it has poor decolorization effect on water-insoluble dyes such as vulcanization, reduction and coating. From the domestic and international operating experience and results, the method has good decolorization effect, but it consumes a lot of electricity, and it has certain difficulties in large-scale promotion and application.
The decolorization efficiency of dyeing wastewater treatment by strontium oxidation is high, but equipment investment and power consumption have yet to be further reduced. 
2.2.3 Electrolysis method  Table 1 Application of biological treatment process of domestic printing and dyeing wastewater
| enterprise | Processing capacity (m 3 /d) | Treatment process | Built time (year) | Investment (ten thousand yuan) |
| Suzhou Dye Factory | 90～100 | Biological turntable (treatment of phenol-containing wastewater) | 1977 | 3.5 |
|  | 1500 |  |  | 326 |
| Wuxi Dye Factory | 1200 | Surface aeration | 1980 | 118 |
| Changzhou Dye Factory | 3500 | Biochar tower | 1978 | 448 |
| Nanjing Chemical Plant | 4800 | Tower biological aeration | 1984 | 455 |
| Shanghai Dyeing Fifth Factory | 2400 | Multi-level push flow exposure | 1980 | 93 |
| Shanghai Auxiliary Factory | 1800 | Biological fluidized bed (activated carbon carrier) |  | 400 |
| Shanghai Dyestuff Institute | 50 | Biochar tower |  | 8 |
| Shanghai Dyeing and Chemical Plant | 2500 | Multi-level push flow exposure | 1984 | 241 |
|  | 4000 | Carrousel biogas aeration tank | 1989 | 1300 |
| Beijing Dye Factory | 150 | Jet aeration | 1989 | 887 |
| Dalian Dyestuff Factory | 150 | Blast aeration (secondary biochemistry) (high concentration influent) |  | 189 |
| Qingdao Dye Factory | 2500 | Pressurized biochemical tower (pre-step anaerobic treatment) | 1990 | 15972 |
| Henan Chemical Plant | 4800 | Surface aeration | 1984 | 222.6 |
| Anyang Dye Factory | 1200 | Multi-stage push surface aeration | 1992 | 120 |
| Jining Yihua | 3000 | Blast aeration - biological contact oxidation (East) |  | 400 |
|  | 1500 | Blast aeration - biochar tower (west) |  | 400 |
| Chuanqing Chemical Factory | 350 | Surface accelerated aeration |  | 98.5 |
| Sichuan Dye Factory | 2400 | Delayed aeration (surface exposure) contact oxidation | 1985 | 356 |
| Luoyang Chemical Factory | 100 | 2m biological turntable | 19801 | 30 |
Electrolysis has a good treatment effect on the treatment of printing and dyeing wastewater containing acid dyes, and the decolorization rate is 50% to 70%, but the treatment effect on wastewater with deep color and high CODCr is poor. The electrochemical properties of dyes show that the order of CODCr removal rate of various dyes in electrolytic treatment is: sulfur dye, vat dye > acid dye, reactive dye > neutral dye, direct dye > cationic dye. This method is currently being promoted and applied. 
2.3 Biological treatment of printing and dyeing wastewater Since the 1970s, domestic printing and dyeing wastewater has been mainly treated with biological treatment, accounting for more than 80%, especially in aerobic biological treatment. From the current situation, the surface accelerated aeration and contact oxidation methods account for the majority of the biological treatment of printing and dyeing wastewater in China. In addition, blast aeration activated sludge method, jet aeration activated sludge method, biological turntable, etc. are also applied, and the biological fluidized bed is still in the experimental application stage. However, since the removal rate of the color of the organism is not high, it is generally about 50%, so when the chromaticity of the effluent is high, it needs to be supplemented by physical or chemical treatment. Table 1 shows the application of biological treatment process of domestic printing and dyeing wastewater. 
The aerobic biological treatment has obvious effect on BOD removal, generally up to 80%, but the chroma and COD removal rate are not high, especially for the wide application of chemical pulp, surfactant, solvent and pebble-base reduction technology such as PVA. Not only the COD of printing and dyeing wastewater reaches 2000~3000mg/L, but also the BOD/COD is reduced from 0.4~0.5 to 0.2. The simple aerobic biological treatment is more and more difficult, and the effluent is difficult to reach the standard; The high operating cost of aerobic processes and the problem of excess sludge treatment or disposal have always been a difficult problem in the field of wastewater treatment. According to the data, the general sludge treatment or disposal costs account for 50% to 70% of the total sewage plant costs (foreign), and also account for about 40% in China. Due to the above reasons, the anaerobic biological treatment technology of printing and dyeing wastewater has begun to receive people's attention. It is increasingly important to explore new technologies for printing, dyeing and wastewater treatment with high efficiency, low consumption and investment.
The main treatment structure for anaerobic anaerobic tanks is anaerobic tanks. Fukunaga N. et al. modified the traditional digester tanks and filled the tank with fixed microorganisms, mainly the genus Alcaligenes. The azo gene, triphenylmethane gene and mononitrogen gene polymer in the dye can be decomposed by anaerobic reaction, usually under moderate temperature conditions (37 ° C), hydraulic retention time 6 h, color of sewage containing mainly methyl red dye. Can be completely removed. Studies have shown that anaerobic treatment of silk printing and dyeing wastewater, HRT = 1.0 ~ 1.1d, COD removal rate of 74% ~ 82%, decolorization rate: black 51%, purple red 94%, rose red 96%, eggplant purple 30% , red 55%. The medium- and long-term operation results of direct treatment of high-concentration dye wastewater by UASB and pipeline anaerobic digester showed that the chromaticity and COD removal rate in wastewater were stable at 80% and 90%, respectively.
In order to explore new technologies for printing, dyeing and wastewater treatment with high efficiency, low consumption and low investment, in recent years, a large number of experimental studies have been carried out on the combination of anaerobic method and aerobic method, which has achieved great success. At this time, the anaerobic treatment combined with the aerobic method is not a conventional anaerobic digestion, and its hydraulic retention time (HRT) is generally 3 to 5 hours, and only hydrolysis and acidification occur. This process is mainly for the high-biodegradability of some high-molecular substances in printing and dyeing wastewater. It is expected that they will hydrolyze and acidify in the anaerobic zone and become smaller molecules, thus improving the biodegradability of wastewater. Aerobic treatment creates conditions. This process is used to better solve the problem of PVA and dye treatment. Another major feature of this process is that all of the excess sludge produced in the aerobic section is returned to the anaerobic section, and the anaerobic section has a longer solid residence time (SRT), which is beneficial to sludge anaerobic digestion, thereby significantly The amount of residual activated sludge in the entire system is reduced. Therefore, the anaerobic section in the anaerobic-aerobic system has a dual role: first, pretreatment of the wastewater, improvement of its biochemical properties, adsorption and degradation of a part of organic matter; second, digestion of the remaining sludge of the system.
Using this process, two processes have been developed at present: anaerobic-aerobic-biochar contact process; anaerobic-aerobic bio-rotary process. Both processes have their own characteristics in terms of equipment and process. 
2.3.1 Anaerobic-aerobic-biochar contact oxidation process The main design parameters are as follows: regulation tank: HRT 8～10h; anaerobic tank: HRT 3～5h; aerobic tank: HRT 6～8h; biochar pool: HRT 1~2h.
The enthalpy test and practical application show that under the above operating parameters, the anaerobic-aerobic-biochar process can completely meet the national emission standards for printing and dyeing wastewater with CODCr of 800-1000 mg/L, and then further processing. It can also be reused, and the sludge of the system tends to balance itself. At present, many production plants have adopted this process, and the longest operation time is more than 5 years. The treatment effect is stable, and the sludge has never been discharged, and the sludge in the anaerobic tank has not been excessively grown. 
2.3.2 Anaerobic-aerobic biological turntable ä¸²è” The anaerobic biological turntable is connected with the aerobic biological turntable for dyeing wastewater treatment, and good results have also been achieved. In the process, there are sludge separation and reflux devices for anaerobic and aerobic processes, and the excess sludge of the entire system is returned to the anaerobic biological turntable. One is to increase the biomass and thus the total hydraulic retention time, and the other is to digest excess activated sludge inside the system. The process is also characterized by both fixed growth and suspension growth. The COD removal rate and the decolorization rate can be further improved by adding a flocculating agent to the turntable. The removal rate of COD, chromaticity, etc. in the process is more than 70%. Appropriate addition of a small amount of flocculant, the CODCr, chroma removal rate can be increased by 15% to 20%. Further increasing the concentration of suspended sludge in the anaerobic tank can also improve the decolorization rate and the COD removal rate. However, the metal components of the turntable in the process are corroded and need further research and solution. 
3 alkali reduction wastewater treatment method
According to the data, the mature technology for treating alkali-reduced wastewater is still a blank in China. In the study of the treatment of this wastewater, chemical methods are generally used, and chemical removal of terephthalic acid has a good effect, but there are still many problems.
The theoretical basis for the treatment of alkali-reduced wastewater by hydrazine chemical method is: alkali-reduced wastewater is neutralized with acid to make the pH value reach 4-6, the terephthalic acid is precipitated, the alkali-reduced wastewater of terephthalic acid is removed and the polyester is simulated. In the silk-dyeing wastewater, the wastewater of other processes such as refining, printing and dyeing is mixed. The pH value of the integrated wastewater is generally less than 11, and the CODCr is not more than 1400mg/L. In this case, the biochemical method is used for treatment, and then the material is treated. National emission standards can be met.
 The process of alkali reduction wastewater treatment is: alkali reduction wastewater → adjustment tank → neutralization tank → PE filter → effluent mixed with other wastewater to further biochemical treatment.
 The method of chemically precipitating terephthalic acid as alkali reduction wastewater pretreatment technology and then using biotechnology to treat integrated wastewater is an effective method for treating high concentration polyester silk screen printing and dyeing wastewater. It is the main way to treat this type of wastewater. The practical application of Shantou Special Economic Zone Xinchang Textile Printing and Dyeing Co., Ltd. shows that the discharge water can meet the national water quality discharge standards when the raw water quality is high and the fluctuation range is large.
废水 The wastewater of this plant is treated with this method and is 5500/m3 wastewater; it covers an area of ​​0.61m2/m3 wastewater; the electricity cost is 0.44 yuan/m3 wastewater; the medicine fee is 0.9 yuan/m3.
The treatment of alkali-reduced wastewater by chemical method has good treatment effect, but there are still some problems: (1) The optimum pH value of the pretreatment process is in the range of 4-6, and the pH value of the alkali reduction wastewater is 12~ 14. Lowering the pH requires a certain amount of acid, which increases the operating cost, which is an urgent problem to be solved. (2) The white powder of terephthalic acid produced by pretreatment has industrial recycling value, but the market sales need to be developed. 
4 Conclusions and problems
The printing and dyeing wastewater is a kind of wastewater with large water volume, high chroma and complex composition, and the water quality varies widely. In urban water sewers and sewage treatment plants, the wastewater is firstly pre-treated in the factory to achieve centralized treatment after urban sewer discharge standards. The pre-treatment and discharge of wastewater can improve the quality of sewage, reduce the treatment load of urban sewage plants, and facilitate different pretreatment methods according to different wastewater quality. In the final treatment of printing and dyeing wastewater, the removal of organic matter is generally based on biological methods. For printing and dyeing wastewater that is difficult to biodegrade, it is suitable to use anaerobic (hydrolysis)-aerobic combined treatment. For printing and dyeing wastewater which is easy to biodegrade, A biological treatment is used. The removal of chromaticity is generally based on physicochemical methods. For large-scale, high-processing plants, electrolysis, chemical flocculation, and ozone oxidation can be used. For small-scale plants, slag filtration can be used.
From the current situation of wastewater treatment technology in China's dye industry, although after years of efforts, a number of practical technologies have been obtained and many problems have been solved, but there is no substantial breakthrough in general, especially the product structure and factory layout are unreasonable. The existence of factors has increased the difficulty of wastewater treatment. Therefore, it is believed that the fundamental solution to the problem of wastewater is technological reform, which uses advanced production processes to reduce or eliminate wastewater. There are many successful examples in this area. For example, the production of aniline and o-toluidine reduces the reduction of iron powder to hydrogenation reduction, completely eliminating the pollution of iron mud water. Another example is the reduction of sodium sulfide by hydrogenation reduction for aminoanisole. The production has completely eliminated the sulfur-containing wastewater.
Prevention and treatment of pollution from printing and dyeing wastewater are two aspects that complement each other. If both preventive measures and various methods are used to actively control and use the treated water cycle, this will not only reduce water consumption, but also effectively Reduce the environmental pollution of printing and dyeing wastewater.
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