Photo-Fenton and biological integrated process for degradation of a mixture of pesticides

A solution of mixed pesticides (alachlor, atrazine, chlorfenvinphos, diuron, isoproturon) was considered for degradation employing photo-Fenton as a preliminary step before biotreatment. Photo-Fenton degradation is an important sub-process in the integrated photobiological process for removal of biorecalcitrant chemicals. Shortening the photo-Fenton treatment time has a critical impact on the economical feasibility of the integrated process. In this study, photo-Fenton was proved to enhance biotraitability of a mixture of biorecalcitrant substances (pesticides). During the photocatalytic process, dissolved organic carbon (DOC) measurements, liquid and ionic chromatography analyses, acute toxicity evaluation using Microtox™ and the Zahn–Wellens biodegradability testing were provided to characterize the photo-treated solutions. In order to find out the best moment for coupling of photocatalytic and biological processes, different times of photo-Fenton pretreatment were tested for biotreatment. The partially photo-treated solutions were fed to eight parallel continuously operated packed-bed bioreactors during 28 days. Considering the coupled system, it was shown that the pre-treated solutions obtained with only 1 g l−1 H2O2 (irradiation time, t30 W = 0.6 h) exhibited higher than 80% of DOC degradation. In this case, the packed-bed bioreactors contributed to more than 50% of the total carbon conversion of the pesticide solution.