Fe3+- IDS as a new green catalyst for water treatment by photo-Fenton process at neutral pH

In this work, a new green and fully biodegradable (96% after 28 days) catalyst, Fe3+-iminodisuccinate complex (Fe-IDS), was prepared, characterized and applied in Fenton processes (dark and photo-Fenton) for water treatment, using phenol as model organic pollutant. Experiments were performed both in dark and under solar/UV-C radiation to evaluate the effect of the light source and [H2O2] (fixed at 5.3 mM)/[Fe-IDS] ratio on the catalytic degradation of phenol (50 mg L−1). Subsequently, photo-Fenton IDS supported process was compared to other advanced oxidation processes (AOPs) (namely, conventional Fenton at pH 3 and H2O2 photolysis, under solar and UV-C irradiation, respectively). The best results (54% and 49% COD removals for solar and UV-C based processes, respectively) were obtained using a [H2O2]/[Fe-IDS] molar ratio of 250 (R250), corresponding to 0.021 mM of Fe-IDS followed by R500 (0.01 mM of Fe-IDS) and R150 (0.035 mM of Fe-IDS). Process efficiency was in the order solar/Fe-IDS/H2O2 >UV-C/Fe-IDS/H2O2 >Fe-IDS/H2O2 (k = −0.0114, −0.0073 and −0.0018 min−1 respectively) for R250. A complete removal of phenol in terms of COD was obtained for solar/Fe-IDS/H2O2 and UV-C/Fe-IDS/H2O2. Furthermore, the application of Fe-IDS complex for real industrial (olive oil mill) wastewater treatment was also investigated (initial COD in diluted sample 2.4 g L−1). At constant H2O2 concentration (58.82mM), the best performance in terms of COD removal (55%, k = 0.0031 min−1) and biodegradability (BOD5/COD increased from 0.16 to 0.45) was obtained for the condition R150 (0.37 mM of Fe-IDS). Fe-IDS allows to overcome the main limitation (acidic pH) of conventional (photo)Fenton process, making the IDS supported (photo)Fenton an attractive option for water and wastewater treatment in a wide pH range.