Advanced oxidation of commercial herbicide mixtures: experimental design and optimization

ALEJANDRO LOPEZ; CRISTINA ZALAZAR; ANDREA COLL; MAIA LESCANO

Congreso; The Fifth International Symposium on Environmental Biotechnology and Engineering (5ISEBE); 2016

Advanced oxidation processes (AOPs), a special kind of wastewater treatment technologies, have been successfully applied for recalcitrant pollutants degradation such as herbicides. The studies are generally performed for individual compounds at higher concentrations than those found in the environment and there are only few researches addressing the degradation of mixtures in a common basis. The application of aqueous commercial herbicide mixtures is nowadays a common practice in agriculture-intensive South American countries. Glyphosate is combined, for example, with other herbicides such as 2,4-dichlorophenoxyacetic acid (2,4-D) and atrazine. The disposal of aqueous herbicide wastewaters is still an unresolved environmental issue in many of these countries. An advanced oxidation technology like the UV/H2O2 process is an effective and attractive alternative to treat this kind of contamination. The UV/H2O2 process has certain advantages in comparison with the most renowned AOPs like relatively low capital and operating costs as well as simplicity in its operation.In this study, the suitability of the UV/H2O2 process for commercial herbicide mixtures degradation (glyphosate, 2,4-D and atrazine) is analyzed. Optimization of specific operating conditions like H2O2 to Total Organic Carbon molar ratio (R) and pH is also assessed. Experimental runs were carried out in a batch photo-reactor, samples were taken each one hour, reaction temperature was set at 25 ºC and radiation was supplied by two low pressure mercury vapor lamps (λ = 253.7 nm). Optimization of the selected operating conditions was assessed by applying the response surface methodology (RSM) technique based on performing a minimum set of experiments adequately distributed in the experimental region tested (1≤R≤18, 3≤pH≤10). A 3-level full factorial design with two factors (R, pH) was selected. The Total Organic Carbon (TOC) conversion (%) at 8 hours was defined as the response. Results have shown that second-order polynomial regression model could well describe and predict the system behavior within the tested experimental region. The model satisfies the assumptions of the analysis of variance (ANOVA) and according to the probability value for calculated Fisher F-test (p<0.05) as well as the coefficient of determination value (R2>0.9) it can be observed that the model is statistically significant. Under the optimum conditions (R close to 5 and neutral pH; TOC conversion>60%) experimental values agreed with the modeled ones confirming the significance of the model and highlighting the success of RSM for UV/H2O2 process optimization. The UV/H2O2 process could be suitable and promising for aqueous commercial herbicide mixtures degradation. The optimum operating conditions found seemed to be attractive for real field applications.