Treatment of pesticide rinsate towards reuse by photosensitized Fenton-like process

A Fenton-like process with combination of dye has been used to enhance the treatment of carbofuran (2,3-dihydro-2,2-dimethylbenzofuran -7-yl methylcarbamate) pesticide rinsate. Results showed that as compared to Fenton-like process, this photosensitization Fenton-like process improved the degradation efficiency of carbofuran rinsate significantly. Among the conditions studied, the optimum dosage for the complete destruction of carbofuran molecular structure was found under a [H2O2]0/[Fe3 + ]0 ratio of 30–35 and a [Dye]0/[Fe3 + ]0 ratio of 2%, respectively, after an irradiance of 500 W/m2 for 20 min. As a result, the COD degradation efficiency of rinsate could be promoted from 37.1 to 61.2% and 66.0% by an addition of methylene blue (MB) and alizarin red S (ARS), respectively. Nevertheless, ARS showed a much more effective acceleration effect on the mineralization and microtoxicity reduction of carbofuran than MB. A mineralization efficiency of 57.2% and a microtoxicity reduction of 90% could be achieved with the addition of ARS. Because of its quinone structure unit, the dye ARS could play a role like hydroquinone to recycle Fe2 + from Fe3 + , resulting in one more catalytic effect on the reduction of Fe3 + and thus the mineralization and microtoxicity reduction of carbofuran was greatly promoted in the presence of ARS. In addition, it was found that carbofuran molecules could be decomposed quickly to lower-molecular-weight intermediates and even mineralized by attacking of hydroxyl radicals. Carbofuran was found to be decomposed to carbofuran phenol, 3-oxo carbofuran phenol, and 3-hydroxyl carbofuran phenol initially, and then further be degraded to smaller molecules, such as NO3−, CH3COOH, (COOH)2 and CO2. Accordingly, it was believed that the Fenton-like process along with the aid of a photosensitizer, such as ARS, under an appropriate ratio could be a feasible and potential technology for the treatment of pesticide rinsate.