Treatment of Organic Wastewater Containing High Concentration of Sulfate by Crystallization-Fenton-SBR

Abstract

In this study, a process consisting of cooling crystallization, Fenton reactions, and a sequencing batch reactor was investigated for the treatment of organic wastewater with high chemical oxygen demand (COD) and sulfate from a chemical company. Cooling crystallization was first employed to remove sulfate from the wastewater. At 4.°C, sulfate concentration was reduced from 212 to 96. g/L, and total wastewater volume decreased by 49.1% through two-stage cooling crystallization. COD concentration was increased from 18. to 18.5 g/L due to the precipitation of Na2SO4 crystals mainly containing crystal water. The effluent was then treated by Fenton reactions. At pH 2., 8. mmol/L of ferric/ferrous, 4 mL/L of 3% H2O2, and a duration of reaction of 6 min, COD removal efficiency maximized at 77.9%, and COD concentration in the effluent leaving the Fenton reactions was 4,1 mg/L. At last, the mixture of the effluent from the Fenton reactions and sewage at a volume ratio of 1∶4 was treated by a sequencing batch reactor (SBR) in which the microorganisms were acclimated to be sulfate tolerant. The efficiency of COD removal by the SBR steadily exceeded 85%, and COD concentration leaving the SBR was below 15 mg/L. These data showed that the three-step process was cost-effective for the treatment of high-salt organic wastewater.