Study On Treatment Processes Of The Wastewaters From Heat-Sensitive Dyes Production

The wastewaters from heat-sensitive dyes production are typical fine chemical wastewater with strong COD, high salinity and refractory organics. The qualities of heat-sensitive dyes' wastewater cannot fit in with the discharge limits as the wastewaters were treated by conventional physical-chemical and biological processes. The treatment process of the heat-sensitive dye's wastewaters from a fine chemical plant in Shandong Province was developed in this research. First, the evaporative desalination, coagulation-precipitation, and neutralization-precipitation were used for pretreatment, respectively, according to different characteristics of the wastewaters. Then, the pretreatment effluents and other wastewaters which needn't be pretreated were mixed, and treated using biological process. Afterward the Fenton oxidation process was used for treating the secondary effluent. Finally, the effluent of Fenton oxidation unit was treated biologically in a subsequent biological reactor (SBR), so that the final effluent quality could achieve the discharged standard.The experimental results showed that through the physical-chemical pretreatment and biological treatment, the residual COD and NH3-N concentrations were from 300mg/L to 400mg/L, and from 60mg/L to 70mg/L, respectively. The optimal pH value, H2O2 dose, FeSO4·7H2O dose and reaction time were 3.5～4.0,1.0 mL/L,0.49 g/L,120 min, respectively, for treating the secondary effluent using Fenton oxidation process. Under optimal conditions, the COD removal effiency of the Fenton process was about 50%. And the biodegradability of the the secondary biological process effluent was improved obviously through Fenton oxidation, the ratio of BOD to COD was increased from 0.09 to 0.35. The effluent of Fenton oxidation unit was further treated biologically in a SBR. Both COD and NH3-N concentrations were lower than 100 mg/L and 15mg/L, respectively, in the final effluent after 10 hours aeration. This means both COD and NH3-N concentrations in the final effluent could reach the first grade discharge standards of Intergrated Wastewater Discharge Standard (GB8978-1996). Therefore, it was possible that the integrated process of physical-chemical pretreatment, biological treatment, Fenton oxidation and SBR process used for treating heat-sensitive dyes' wastewaters, but the operation cost of this combined process was relatively expensive.