Disinfection of urban wastewater by a new photo-Fenton like process using Cu-iminodisuccinic acid complex as catalyst at neutral pH

Photo-Fenton process is among the most effective advanced oxidation processes (AOPs) in urban wastewater treatment and disinfection, but its application as tertiary treatment at full scale has not been a feasible/attractive option so far because optimum conditions are typically achieved under acidic pH. In this work a new photo Fenton like process (UV-C/H2O2/IDS-Cu) using iminodisuccinic acid (IDS)-Cu complex as catalyst, was compared to other processes (UV-C/H2O2/Cu, UV-C/H2O2/Fe, H2O2 and UV-C) in urban wastewater disinfection. Since this is the first time that IDS-Cu complex was isolated and used as catalyst, preliminary tests to evaluate the mineralization of a model compound (phenol, 25 mg L−1 initial concentration) in water by UV-C/H2O2/IDS-Cu were carried out. Almost complete mineralization of phenol (95%) was observed after 60 min treatment, being the process more effective than all other investigated AOPs (Fenton and photo-Fenton processes). This process was also proven to be more effective in the inactivation of E. coli (complete inactivation (3.5 log units) in 10 min) at natural pH (7.8 ± 0.5) in real wastewater, than the other processes investigated. Unlike of what observed for E. coli inactivation, the investigated processes only partially inactivated total bacterial population (from 18% for UV-C to 43% for UV-C/H2O2/Cu), according to flow cytometry measurements. In particular, Cu based photo-Fenton processes resulted in the higher percentage of inactivated total cells, thus being consistent with the results of E. coli inactivation. It is worthy to note that, as H2O2 was decreased, UV-C/H2O2/Cu-IDS was more effective than UV-C/H2O2/Cu process. Moreover, the formation of small and large clusters decreased in the presence of Cu and Cu-IDS complex, and process efficiency improved accordingly; these results show that Cu based AOPs can more effectively disaggregate clusters, thus making disinfection process more effective than Fe based AOPs.