International audienceIn 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•–) 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•– with 4-tert-butylphenol (4tBP) kSO4•–,4tBP = (4.21 ± 0.22) × 109 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 mM), 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•– has a similar reactivity with EDDS (6.21 × 109 M–1 s–1) and 4tBP (4.21 × 109 M–1 s–1). However, the secondary generated radicals (mainly Cl2•–) 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

The present work describes in detail the chemical structure of the complex Fe(III)–EDDS and the predominance of different species with respect to pH. These results were obtained with ab initio calculations. From the photoredox process, the formation of hydroxyl radical was confirmed, and HO(•) is the main species responsible for the degradation of the organic compound present in aqueous solution. The degradation of 4-tert-butylphenol (4-t-BP), used as a model pollutant, was investigated in different conditions. For the first time, the second-order rate constant of the reaction between HO(•) and 4-t-BP and the formation rate of HO(•) (R(HO(•))(f)) from the photochemical process were evaluated. Through the degradation of 4-t-BP, the effect of Fe(III)–EDDS concentration, oxygen, and pH was also investigated. The pH, which plays a role in the iron cycle and in the Fe(III)–EDDS speciation, was noticed as an important parameter for the efficiency of 4-t-BP degradation. Such a result could be explained by taking into account the complex speciation and presence of a predominant form (FeL–) up to pH 8. These results are very useful for the use and optimization of such iron complexes in water treatment processes.