Study On The Treatment Of Dyeing And Printing Wastewater By The Combined Processes Of Sponge Iron Filtration, Hydrolysis Acidification And Membrane Bioreactor

The dyeing and printing wastewater is one of the most difficult industrial wastewater to be treated, which has many special characteristics including large flow capacity, high content of organic pollutants, heavy color and a low ratio of BOD5/COD and so on. The two major polluting sources are desizing and dyeing processes, which produce a very high proportion wastewater in the total printing and dyeing technical processes, therefore, it is very important to reduce the organic pollutants in desizing and dyeing wastewater to improve the quality of the drainage wastewater.This study treats the simulated dyeing and printing wastewater by the combined processes of sponge iron filtration, hydrolysis acidification and membrane bioreactor. The sponge iron filter column is used for the pretreatment of dyeing wastewater, then the treated dyeing wastewater and desizing wastewater mix into the hydrolysis acidification pool to improve the biodegradability of wastewater, and membrane bioreactor effectively removes the organic pollutants in the wastewater at last, making the drainage wastewater to meet the discharge standards.The experimental results show that the sponge iron filter column can effectively remove the color of dyeing wastewater. The optimum operating parameters for the sponge iron filter column are that filter velocity is 4m/h, influent pH is 10 and the particle size of sponge iron is 3～5mm. Under these optimum conditions, the average effluent chroma is 45 times and decolorization rate reaches 92.6% in a filter cycle, and the filter period and water production are 166h and 470L respectively; After activation and backwashing, the sponge iron can almost recover the original state, the average decolorization rate is still above 90%, and the filter period and water production are roughly equal to those before activation. The observation of the sponge iron by Scanning Electron Microscope (SEM) find that the sponge iron before reaction is loose and porosity, while after reaction the surface of sponge iron is covered with full of the reaction products. The sponge iron in the top of the filter column is more passivated than that in the middle and bottom; The surface analysis by X-ray diffraction (XRD) discovers that after reaction the sponge iron is covered by the iron oxides and hydroxides, which mainly are Fe2O3, Fe (OH)3, Fe+3 (OH)3, FeOOH, FeO(OH) and so on; The composition of the reaction products in the top of the filter column is more complicated.When the hydraulic retention time (HRT) of the hydrolysis acidification pool is 10h, the COD removal rate of the wastewater is low, about 30%, and the effluent COD is 400～500 mg/L, while the color removal rate is about 70% and the effluent color is below 20 times; The ratio of BOD5/COD is from 0.25～0.35 increasing to 0.35～0.5, so the biodegradability of the wastewater improves significantly, which is in favor of the subsequent aerobic biological treatment.When the membrane bioreactor (MBR) operates at different HRT, the effluent COD and color are below 100mg/L and 10 times respectively. The best HRT of membrane bioreactor is 8h by comparing the treatment results of different HRT, and the effluent COD is between 30 and 45mg/L under this condition.Under the optimal conditions, the removal rates of COD and color are above 90% and 98% by the combined processes, and the concentrations of COD and color are below 50mg/L and 10times respectively. The quality of effluent meets the discharge standards of dyeing and printing industrial wastewater in Shandong Province.