Integrated Electrochemical Oxidation and Biodegradation for Remediation of a Neonicotinoid Insecticide Pollutant.

Abstract

A novel integrated electrochemical oxidation (EO) and bacterial degradation (BD) technique was employed for the remediation of the chloropyridinyl and chlorothiazolyl classes of neonicotinoid (NEO) insecticides in the environment. Imidacloprid (IM), clothianidin (CL), acetamiprid (AC), and thiamethoxam (TH) were chosen as the target NEOs. Pseudomonas oleovorans SA2, identified through 16S rRNA gene analysis, exhibited the potential for BD. In EO, for the selected NEOs, the total percentage of chemical oxygen demand (COD) was noted in a range of 58-69%, respectively. Subsequently, in the biodegradation of EO-treated NEOs (BEO) phase, a higher percentage (80%) of total organic carbon removal was achieved. The optimum concentration of NEOs was found to be 200 ppm (62%) for EO, while for BEO, the COD efficiency was increased up to 79%. Fourier-transform infrared spectroscopy confirms that the heterocyclic group and aromatic ring were degraded in the EO and further utilized by SA2. Gas chromatography-mass spectroscopy indicated up to 96% degradation of IM and other NEOs in BD (BEO) compared to that of EO (73%). New intermediate molecules such as silanediamine, 1,1-dimethyl-n,n'-diphenyl produced during the EO process served as carbon sources for bacterial growth and further mineralized. As a result, BEO enhanced the removal of NEOs with a higher efficiency of COD and a lower consumption of energy. The removal efficiency of the NEOs by the integrated approach was achieved in the order of AC > CL > IM > TH. This synergistic EO and BD approach holds promise for the efficient detoxification of NEOs from polluted environments.