(A) the water quality characteristics of wastewater to cotton and blended products mainly printing and dyeing plant, discharged a variety of wastewater and water quality characteristics are:
1) desizing wastewater desizing wastewater is alkaline organic wastewater containing a variety of pulp decomposition products, fiber debris, acids and enzymes and other pollutants. The degree of pollution varies depending on the type of pulp. In the past, most of the natural starch for pulp, high BOD in the water, in recent years, gradually replaced by chemical pulp, such as polyethylene glycol (PVA), the wastewater in the BOD is very low, but the COD is very high, which reduces the biodegradation performance of the wastewater.
2)Boiling and refining wastewater wastewater is dark brown, containing alkali concentration of about 0.3%, wastewater BOD and COD are as high as thousands of milligrams / liter.
3)Bleaching wastewater water volume, light pollution, can be directly discharged or recycled back to use.
4)Mercerizing wastewater containing sodium hydroxide 3% to 5%, generally recovered by evaporation and concentration, the process can be reused, discharged mercerizing wastewater is alkaline, BOD is higher than domestic sewage.
5)Dyeing wastewater is mainly contaminated with organic dyes and surfactants and other additives. The water quality changes greatly, the color is deep and the pH value is high.
6)Printing wastewater is mainly soap washing, washing wastewater. In the use of reactive dyes to use a large number of urea, so the wastewater ammonia nitrogen is high.
7)Finishing wastewater is small, containing a variety of resins, formaldehyde, surfactants and so on. Several representative domestic printing and dyeing plant wastewater quality is shown in Table 16-1.
(B) printing and dyeing wastewater treatment methods
First of all, from the production process to eliminate and reduce the source of pollution. Such as the use of dry printing process to eliminate printing and dyeing wastewater. According to the characteristics of water quality, respectively, recycling, one water multi-purpose; with precipitation, filtration method to recover tulin dyes and magnetized dyes, with more than filtration method to recover reducing dyes, disperse dyes and so on. Secondly, harmless treatment of wastewater. For the alkalinity of wastewater, generally set up a regulating pool and ensure the necessary homogenization time; for the chromaticity, according to the requirements of wastewater discharge and utilization, available coagulation method, adsorption method. Oxidation, electrolysis and other chemical or physical methods of treatment, but also the cultivation of special bacteria in both gas conditions for decolorization. It should be pointed out that the use of coagulation method for direct dyes, reducing dyes, magnetized dyes, disperse dyes, chromaticity, removal effect is good, but for acid dyes, reactive dyes, decolorization effect is poor. Activated carbon has selective adsorption of dyestuffs. It has good adsorption performance for cationic dyestuffs, direct dyestuffs, acid dyestuffs, reactive dyestuffs and other water-soluble dyestuffs, but has poor adsorption performance for sulfide dyestuffs, reducing dyestuffs, paints and other insoluble dyestuffs. The commonly used ozone oxidizer has good decolorizing effect on hydrophilic dyes such as direct dyes, acid dyes, basic cationic and reactive dyes and poor decolorizing effect on hydrophobic dyes such as reducing dyes, sulfur dyes and disperse dyes. A large amount of organic matter in wastewater can usually be treated by biological method to achieve more satisfactory results; for chemical slurries such as PVA, biodegradation or recycling method can be used. In biodegradation, can be used in a high MLSS and two-stage aeration method and anaerobic - aerobic string acid treatment process; in recycling, can be used in gelling salinity (adding borax and sodium sulfate), coagulant method (such as manganese nitrate and borax as a coagulant), more than the filtration method (in Beijing, Shanghai, Henan and other factories have been used).
In short, the selection of printing and dyeing wastewater treatment process, according to the production process using raw materials, product types, processing methods, the process of adding chemicals, dyes, additives, the nature of the final destination of the water as well as the requirements of the final destination, respectively, the use of a first level of chemical and physical chemical treatment or secondary biological treatment. The chemical and physical treatment or the secondary biological method is the main treatment or the tertiary deep treatment.
(3) Selection of wastewater treatment process
1) Firstly, consider the separation of clear and turbid wastewater, and recycle or treat the thicker dyeing wastewater and the wastewater which is not easy to be biodegraded by chemical and physical-chemical method alone, and then mix with the other wastewater to carry out the biological treatment or to be discharged to the municipal wastewater treatment plant for unified treatment;
2) If the water quality is allowed, adopt the treatment method combining with the chemical coagulation and pressurized flotation, and for the small-scale printing, the chemical treatment method combining with the chemical treatment is adopted. Combined with the treatment method, the small printing and dyeing plant can be used for the complete set of domestic devices, running costs are slightly higher, in general, the treated water can meet the requirements.
3) biological treatment can give priority to the activated sludge method, the traditional method of aeration and delayed aeration method can achieve stable results, in the aeration of 4 to 6 hours under the conditions of BOD5 to remove 90%, COD to remove 60 to 70%. Blast aeration sludge load of 0.3~0.5 kg BOD/kg MLSS-day, delayed aeration method using sludge load of 0.1 kg BOD/kg MLS8-day. If the accelerated surface aeration method, the aeration tank and sedimentation tank should be built separately, which is conducive to inhibit the expansion of sludge, management is more convenient, the effluent water quality is stable.
4) When the treatment of water requirements are higher or wastewater treatment for reuse, it is appropriate to increase the biological treatment of adsorption or coagulation filtration device. Anaerobic - good gas - activated carbon process, not only the removal of chemical slurry PVA and chromaticity is good, but also the effluent water quality is good, has been noticed.
5)On biological treatment when using biofilm method:
①Contact oxidation method - using volumetric loading of 2.3 to 5.0 kg BOD / (m - day). Advantage is that the treatment time is short and sludge does not have to flow back, but the gas-water ratio is high, the infrastructure costs and operating costs are slightly higher.
②Bio-turntable - suitable for treatment of small amounts of water in the dyeing plant, such as water in 1OOO meters? / day or less, simple operation, power consumption. The key in the turntable material and turntable before the setting of the regulating pool. Organic load using 15-30 g BOD5/(m - day), hydraulic load using 0.1-0.25 m. /(m-day).
3) Tower Filter - the main feature is to save land, it is an incomplete treatment structure, using volumetric loading of 1.6 to 1.8 kg BOD / (m - day) when the COD removal rate of 40% to 50%, BOD removal rate of 50% to 60%.