Optimizing the photocatalytic process of removing diazinon pesticide from aqueous solutions and effluent toxicity assessment via a response surface methodology approach

Diazinon is one of the most dangerous environment pollutants. In this study, the optimization of removing diazinon from contaminated aqueous solutions was evaluated by advanced oxidation process along with the evaluation of effluent toxicity by Escherichia coli bacteria. The design of the experiments was based on the response surface methodology. Iron oxide nanoparticles and iron oxide/titanium oxide were produced by co-precipitation and col–gel, respectively. The features of produced nanoparticles were investigated by scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) techniques. In this study, the toxicity tests of effluent were performed by the activity of dehydrogenase enzyme reducing Alamar Blue method. Based on statistical analyzes (R2 = 0.996), the values of optimal pH, contact time, and nanoparticle concentration were obtained at 6.75, 65 min, and 550 mg/L in the removal of diazinon, respectively. In this case, the efficiency of removing diazinon was 94.15%. By analyzing the effluent, eight by-products due to the degradation of diazinon were determined with the probability of correct detection above 50%. Based on the Alamar Blue reduction test (ABR), the effective concentrations of 50% (EC50) and the no observed effect concentration (NOEC) for E. coli were obtained 2340 and 18 mg/L, respectively. Based on the results, it was found that the photochemical process TiO2/Fe3O4 has high efficiency on the removal of diazinon and there is a significant relation (p value < 0.05) between dehydrogenase activity of E. coli bacteria and reduction of Alamar Blue.