Case analysis of dyeing and chemical wastewater treatment plant

A dyeing and chemical sewage treatment plant is located in the fine chemical industry park of a city in Zhejiang Province, on the reclaimed beach on the South Bank of Hangzhou Bay East of caoejiangkou. The total floor area of the plant is 282344.61 m2.

The design scale of the sewage treatment plant is 100 thousand m3/d, and the design is divided into three sets of parallel operation. Each design flow is 33 thousand m3/d, and the regulating pool, utility facilities and pumping stations are built at 100 thousand m3/d scale. The first stage of the first stage project is folded plate flocculation tank, cavitation air flotation tank, anaerobic pool and combined MSBR biochemical reaction pond. The proportion of industrial wastewater and domestic wastewater entering the sewage treatment plant is about 4:1. Among them, the industrial wastewater mainly includes dye, medicine, chemical fiber and other production wastewater, accounting for about 90%. The designed effluent quality meets the secondary discharge standard of dyestuff industry specified in integrated wastewater discharge standard (gb8478-96).

1. Process flow

The combination of physicochemical and biochemical treatment process was adopted. The physicochemical part adopts coagulation air flotation, while the biochemical part adopts anaerobic and combined MSBR reaction tank.

2 conclusions and suggestions

(1) the results of continuous operation of the treatment system show that it is feasible to adopt the combination of physicochemical and biochemical processes for the treatment of large and medium-sized wastewater treatment projects with dye industrial wastewater as the main wastewater, and the effluent quality basically meets the discharge standard. Among them, MSBR biochemical tank has high COD and BOD removal rate.

(2) the improvements in the process design are as follows: ① the lifting pump room should be changed to facilitate the control of dosing amount after the regulating tank; ② the inflow flow is too large, and the waste water from the air flotation tank is serious, because the waste water is mainly disperse dyes, it is recommended to change the air flotation process to sedimentation process; ③ the anaerobic tank can be considered to be built together with the MSBR tank to save land resources and investment costs. Considering that the wastewater treatment plant is mainly dyestuff wastewater, its biodegradability is poor. The recommended HRT should be greater than 16 h. 4. Because of the high content of surfactant in the water inlet, the MSB R biochemical tank is too much foam, causing the sludge to float up and seriously affecting the normal operation of the biochemical tank. It is suggested to add a defoaming device in the aerobic zone and the main aeration area of the MSBR pool. It has achieved good results, but it is inconvenient in operation; ⑤ the effluent color is still relatively high, the decolorization process should be added, and the subsequent process of MSBR series air flotation is recommended.