Pretreatment and biodegradability enhancement of DSD acid manufacturing wastewater.

Two advanced oxidation processes, Fenton's reagent oxidation and ozonation, were used for pretreatment of a 4,4'-diaminostilbene-2,2'-disulfonic acid (DSD-acid) manufacturing wastewater on a laboratory scale. The results showed that both methods are suitable for partial removal of chemical oxygen demand (COD) and color as well as the enhancement of biodegradability of DSD-acid manufacturing wastewater before the conventional biological treatment. Fenton's reagent oxidation by 9.0 g/L H2O2 and 150 mg/L Fe2+ and ozonation by 7.5 g/L O3 led to an improved biodegradability (BOD5/COD = 0.3). Fenton's reagent oxidation in combination with Fe3+ coagulation has shown to effectively remove COD and color. About 90% of COD and 95% of color removals were obtained at the optimum condition, oxidation by 150 mg/L Fe2+ and 2 g/L H2O2, followed by two-stage coagulation with 5 g/L and 2 g/L FeCl3, respectively.