On printing and dyeing wastewater

     Among all the industries, the COD emission of textile printing and dyeing industry ranks the fourth. From 1998 to 2003, the proportion of COD emission in paper and food industry decreased year by year, while that of textile printing and dyeing and chemical industry increased year by year. The proportion of textile printing and dyeing industry increased from 4.7% to 5.6% in 2003, and increased by 0.9% in five years. According to statistics, the total amount of wastewater discharged from textile industry in 2003 was 1.413 billion tons, of which about 1.13 billion tons (accounting for 80% of textile printing and dyeing wastewater). Due to the large amount of wastewater generated in the dyeing and finishing process, it can generally reach 70% – 90% of the water consumption of printing and dyeing enterprises. At present, China produces 4-5 tons of waste water per 100 meters of cloth. And with the growth of China’s textile export output, it is bound to bring the increase of wastewater.

Printing and dyeing wastewater is composed of auxiliaries, dyes and sizing materials discharged from the dyeing and finishing process, with little toxicity. The color of printing and dyeing wastewater is caused by the discharged dyes. About 10% – 20% of the dyes are discharged with the wastewater in the printing and dyeing process. The dyes in the wastewater can absorb the light, reduce the transparency of the water body, affect the aquatic organisms and microorganisms, which is not conducive to the self purification of the water body, but also causes visual pollution, which will seriously affect human health. Moreover, with the increase of color varieties, dyeing and finishing processes are constantly updated, some of which lead to the aggravation of pollution. For example, in the popular alkali reduction process in recent years, due to the dissolution of a large amount of terephthalic acid in the fiber, the COD content in the waste water is greatly increased, and the COD content in the waste water can reach 20000-80000mg / L; similarly, the COD content in the wastewater of island silk process is as high as 20000-100000 mg / L. The application of these new processes increases the difficulty of printing and dyeing wastewater treatment. Some enterprises have poor quality of environmental protection facilities and even despise operation and management. Due to the enterprise’s unwillingness to invest reasonably in pollution control facilities, some sewage treatment facilities have poor quality in design and construction, short process flow and poor equipment performance. Wastewater treatment is a system engineering with high technical content. From design, construction, equipment selection,

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commissioning to production and operation, all links need professional knowledge and strict specifications, and adjustment should be made at any time according to the change of water quality in the production process, and special technicians are required to practice. But because the enterprise does not pay attention to this, so the allocation of technical personnel is basically vacant, and there is a lack of due training and management. Therefore, the printing and dyeing wastewater treatment industry needs formal and professional environmental protection companies, guided by the scientific outlook on development, comprehensively implement the operation and management technology of printing and dyeing industry, and improve the overall level of printing and dyeing water treatment in China.

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