EFFECT OF FENTON AND PHOTO-FENTON REACTIONS ON THE DEGRADATION AND BIODEGRADABILITY OF 2-NITROPHENOLS AND 4-NITROPHENOLS IN WATER-TREATMENT

Photo-Fenton, Fenton and biodegradation reactions have been investigat ed in detail during the degradation of 2 and 4-nitrophenols. Fenton-ty pe reactions accelerated nitrophenols degradation in comparison with d irect photolysis using pyrex flasks (lambda > 290 nm). The influence o f Fe3+, H2O2, light, temperature, reactant concentration and gas atmos phere was systematically studied. Experimental techniques used involve d total organic carbon determination (TOC), high pressure liquid chrom atography (HPLC), nuclear magnetic resonance (NMR) and spectroscopy (O D). A solution containing 3.6.10(-3) M of 2-nitrophenol was degraded i n ca. 3 h (30-degrees-C) in the dark and in ca. 1 h (30-degrees-C) und er light where continuous photoproduction of the Fenton reagent is ach ieved. This study shows that the hydroxylation of the phenol ring is f ast as compared to the slower concomitant decrease in DOC in dark or l ight processes. Using NMR an explanation is proposed in terms of pathw ays involving direct oxidation of the nitrophenols under study by hydr oxy type radicals. Chemical insight is provided why the photo-Fenton d egradation observed for 2-nitrophenol proceeds at about half the rate than his homologue 4-nitrophenol. Biodegradability of 2-nitrophenol wa s monitored before and after photo-Fenton treatment by biochemical oxy gen demand (BOD) and dissolved organic carbon (DOC) and indicated the formation of substances which are non-biodegradable during photo-Fento n pretreatment.