Sequential coagulation/flocculation and sonolytic oxidation using persulfate and hydrogen peroxide for real rubber processing industry wastewater treatment: Kinetic modelling and treatment cost analysis

Abstract

Rubber processing industry consumes huge quantity of water, uses chemicals and produces enormous quantity of toxic wastewater with high level of chemical oxygen demand (COD), solids and turbidity. In this study, treatability of rubber processing industry effluent using a sequential coagulation-flocculation (CF) followed by sonolytic oxidation was studied with the real wastewater collected from a rubber processing industry located near to Agartala, Tripura, the second largest rubber producing state in India. Initially aluminium sulfate was used as coagulant in the CF process to reduce the COD of the wastewater followed by only ultrasonication (CF + US), sonolytic oxidation using persulfate (CF + US + PS), sonolytic oxidation using hydrogen peroxide (CF + US + H2O2) and sonolytic oxidation using both persulfate and hydrogen peroxide (CF + US + PS + H2O2) as oxidants. Real rubber processing wastewater was also treated with only sonication (US). Firstly, the only CF process (aluminium sulphate dose: 500 mg/L) could reduce the COD of wastewater from 18267 mg/L to 12800 mg/L (COD removal: 29.93 %). Thereafter, CF + US (sonication time: 30 min), CF + US + PS (PS dose: 500 mg/L), CF + US + H2O2 (H2O2 dose: 0.75 mmol/L), and CF + US + PS + H2O2 (PS dose: 500 mg/L and H2O2 dose: 0.75 mmol/L) resulted to effluent COD value to ∼ 6800 mg/L, 4200 mg/L, 3200 mg/L and ∼ 1600 mg/L, respectively. The CF + US + PS + H2O2 process was the best option among the considered combination of treatment techniques to treat the real rubber processing industry effluent in terms of COD removal (%). Kinetic analysis for the degradation of COD in various treatment processes were found to be consistent with pseudo second order kinetic model. The treatment cost analysis revealed that COD degradation by CF + US + H2O2 process cost ∼ 2.5 USD/kg of COD removal with 82.48 % of COD removal.