Photo-Fenton reaction at mildly acidic conditions: assessing the effect of bio-organic substances of different origin and characteristics through experimental design.

Urban-waste bio-organic substances (UW-BOS) have been shown to be capable of extending the photo-Fenton reaction to mildly acidic conditions. In this study, the effects of pH (3-7), UW-BOS, HO and iron concentrations on the photo-Fenton process were systematically assessed using a Doehlert experimental design and response surface methodology for two UW-BOS (CVT230 and FORSUD). Solutions of the model antibiotic sulfadiazine (SDZ) were irradiated in a solar simulator equipped with a 550 W Xenon lamp. The results showed that for UW-BOS contents below 30 mg L, SDZ removal proceeds at pH 5 with similar rates for both CVT230 and FORSUD, regardless of Fe(III) concentration. For 50 mg L of UW-BOS or higher, CVT230 performs better than FORSUD, even for low Fe(III) content (1-3 mg L). In contrast, half-life times of 35-40 min can only be achieved under mildly acidic conditions with FORSUD for iron concentrations higher than 10 mg L. The better performance of CVT230 can be associated with its high hydrophilic/hydrophobic ratio, low E2:E3, higher iron content and possibly higher yields of triplet reactive species generation upon solar irradiation. The most appropriate conditions for each UW-BOS studied are discussed for the first time, which are advantageous for possible engineered applications.