Solar photo-Fenton degradation of herbicides partially dissolved in water

This study evaluates the solar photo-Fenton decontamination of wastewater containing a highly polluted mixture of two common herbicides, one of them partially dissolved. The mixture was composed by the commercial formulations Hierbamina® (479.5 g/L 2,4-dichlorophenoxyacetic acid, 2,4-D) and Gesaprim® (90% atrazine, ATZ), in a 5:9 (v/v) ratio, as they are commonly dosed in Mexico. All solar photo-Fenton experiments were performed in a Compound Parabolic Collector (CPC) pilot-plant with a total volume of 35 L (22 L illuminated volume). The influence of some operating variables (e.g., iron concentration, matrix salinity and initial pollutant concentration) and their relationship to photo-Fenton process efficiency were studied. Experiments were performed at three iron concentrations (5, 10 and 20 mg/L), in two types of waters (demineralized and fresh) and at two initial herbicides amounts (90 and 170 mg/L of ATZ and 50 and 100 mg/L of 2,4-D). Solution ecotoxicity and biodegradability during the photo-treatment was also evaluated, since it has been demonstrated that some photo-degradation by-products of ATZ and 2,4-D can be more toxic and/or persistent than the parent compounds. It was found that 10 mg/L of iron was a suitable concentration, the use of fresh water did not reduce photo-Fenton efficiency and H2O2 consumption becomes more efficient with higher starting pollutant concentration. Moreover, the study of toxicity and biodegradability during photo-Fenton degradation allowed the selection of the most favourable design parameters for the detoxification of the water.