Degradation of dimethoate using combined approaches based on hydrodynamic cavitation and advanced oxidation processes

Abstract

Degradation of dimethoate (DM), an organophosphorus pesticide, present in aqueous solution considered as simulated wastewater was investigated using different approaches based on hydrodynamic cavitation. Initially, the effect of initial concentration of DM was investigated over the range of 20−75 ppm at a constant condition of 4 bar as inlet pressure. The maximum extent of degradation (25 %) was observed for 20 ppm solution using the approach of HC alone. The hybrid approaches of HC + UV, HC+H2O2, and HC + Fenton were subsequently investigated at inlet pressure of 4 bar and pH of 7 (natural pH of solution) using 20 ppm as the initial concentration. Significant increase in degradation for the combination operations such as HC + UV and HC+H2O2 with actual extent of degradation as 30.8 % and 72.5 % respectively was observed. Complete degradation of DM within only 40 min was established in the work using HC + Fenton combination at optimized Fe (II) and H2O2 loadings as 0.9 M and 0.18 M respectively. Also, COD reduction as high as 71.5 % was demonstrated using HC + Fenton combination at much lower Fe (II) and H2O2 loadings as 0.009 M and 0.045 M respectively. The kinetic rate constants were obtained for all treatment approaches using the integral analysis. The toxicity analysis of DM, before and after treatment, was also performed using two bacterial strains as Bacillus subtilis and Pseudomonas aeruginosa. Based on the obtained values of cavitational yield and operational costs based on energy requirements, the different treatment approaches have also been compared. Overall, it was clearly demonstrated that HC + Fenton is an effective treatment approach for the complete remediation of DM and treated effluent also showed no toxicity to the bacteria.