Experimental study on the treatment of high COD metal degreasing cleaning wastewater by coagulation and two-stage Fenton oxidation

Abstract

In this study, based on the water quality characteristics of metal degreasing cleaning wastewater, wastewater treatment by coagulation combined with two-stage Fenton oxidation was proposed. The results showed that when the dosage of PAC was 5 g/L and the dosage of CPAM was 8 mg/L, with an initial pH of 8, rapid stirring at 350 rpm for 3 min followed by slow stirring at 200 rpm for 15 min, the optimal removal rate of chemical oxygen demand (COD) reached 74.08%. Primary Fenton oxidation is mainly aimed at decomposing macromolecular long-chain pollutants and removing some pollutants. The highest COD removal rate was achieved at 95.07% when the dosage of H2O2 was 4 mol/L, the dosage of FeSO4 was 40 g/L, the oxidation lasted for 60 min, the initial pH was 2, the effluent pH was 8, and the settling time was 90 min. The two-stage Fenton oxidation process provided further advanced treatment. With a reagent ratio of 1:0.5, the effluent COD concentration was reduced to 457 mg/L, meeting the third class standard of the `Integrated Wastewater Discharge Standard’ (GB 8978 1996).