Sulfate Radical Photogeneration Using Fe-EDDS: Influence of Critical Parameters and Naturally Occurring Scavengers

In this study, the activation of persulfate induced by Fe(III)-ethylenediamine-N,N'-disuccinic acid (EDDS) under dark and irradiation conditions and the reactivity of the generated sulfate radical (SO4 center dot-) under a wide range of experimental conditions were investigated by means of experimental kinetic analyses and modeling. The Fe(III)-EDDS induced activation of persulfate was found to be efficient across a wide range of pH value (3-7), whereas the second order rate constant of SO4 center dot- with 4-tert-butylphenol (4tBP) k(SO4 center dot-,4tBP) = (4.21 +/- 0.22) X 10(9) M-1 s(-1) was found to be unchanged between pH 2.5 and 8.5. Experimental and theoretical investigations showed clearly that the 4tBP degradation was enhanced in the presence of chloride (10 m.M), whereas an almost complete inhibition was observed in the presence of carbonates (10 mM). For the first time, second order rate constants evaluated by laser flash photolysis experiments revealed that SO4 center dot- has a similar reactivity with EDDS (6.21 X 10(9) M-1 s(-1)) and 4tBP (4.21 X 10(9) M-1 s(-1)). However, the secondary generated radicals (mainly Cl-2(center dot-)) but also greater amounts of hydroxyl radicals formed in the presence of chloride can likely explain the enhancement of the 4tBP degradation rate. These results may have strong implications for the removal of organic pollutants via sulfate radical generation from contaminated waters, especially if the wastewater possesses carbonate and chloride concentrations consistent with those present in aquatic environments.