Improvement in biological oxidation process for the removal of dichlorvos from aqueous solutions using pretreatment based on Hydrodynamic Cavitation

In the present work, the removal of Dichlorvos (DDVP) from aqueous solution was investigated using combined approach of Hydrodynamic cavitation (HC) as pretreatment followed by the biodegradation operated as per the OECD protocol, 301E. Initially, the efficiency of HC reactor based on slit venturi was optimized by varying the inlet pressure (range of 4-7 bar) and pH (range of 4-9). Under optimized conditions established as inlet pressure of 5 bar and pH of 4, subsequent studies for the degradation of DDVP using combined approaches of HC with Ozone (HC + O3) as intensified pretreatment were performed. It was established that the combined approach significantly enhanced the degradation to 84.8% with TOC reduction of 39.4%. Further, biodegradation analysis of HC and HC + O3 pretreated DDVP aqueous solution was performed. A maximum kinetic rate constant as 64.2 × 10−3 day−1 was obtained for pretreated DDVP solution using the HC + O3 combination, which was about 10 times higher as compared to the case where untreated solution of DDVP (kinetic rate constant as 5.3 × 10−3 day−1) was directly used for biological oxidation. Integral method of analysis revealed that the reduction follows the first order kinetics with maximum oxidation rate constant as 64.2 × 10−3 day−1 for the combined approach involving HC + O3 as the pretreatemnt followed by biological oxidation. Overall, it has been demonstrated that HC combined with ozone can be effectively used as pretreatment for improving the biodegradability of DDVP.