Comparison between Fenton and Fenton-like reactions for l-proline degradation

Abstract

Fe/H2O2 and Co/PMS reactions were compared for l-proline degradation under different initial pH values, various transition metal salt and oxidant agent concentrations, as well with and without irradiation. The Fenton reaction took 60 min to degrade 90% of the l-proline, whereas the Fenton-like reaction achieved the same degradation after only 15 min. The best conditions for the Fenton-like reaction resulted from using 0.8 mM of cobalt salt with low PMS concentration (20 mM) at a neutral initial pH and without irradiation. Further experiments were performed using the Co/PMS system to estimate the effects of the other reaction conditions. The results of these experiments showed that pH, reagent concentration, and UV (λ = 365 nm) radiation had no significant effect on the degradation. Additionally, the Fenton-like reaction was made in heterogeneous phase, showing that the reaction proceed equally at same pH than homogeneous phase reaction with no significant effect of phase type used. Significant amount of cobalt was found being leached from the solid media to the water at acidic pH values during the heterogeneous process so the best process conditions were found at neutral pH where the amount of cobalt being leached was found negligible. The heterogeneous Fenton-like process was found feasible to be used for different contaminants degradation with no risk of increased toxicity related with cobalt leachate. The results of this work provide a good evaluation of heterogeneous and homogeneous Fenton-like reaction and suggest that high reagent concentrations are unnecessary for efficient contaminant removal in aqueous phase.