Natural solar activation of modified zinc oxides with rare earth elements (Ce, Yb) and Fe for the simultaneous disinfection and decontamination of urban wastewater

This study investigates the capability of modified zinc oxides (ZnO) with Ce, Yb and Fe towards the simultaneous inactivation of pathogenic bacteria (Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa) and Contaminants of Emerging Concern (CECs, Diclofenac, Sulfamethoxazole and Trimethoprim) under natural sunlight. Several catalyst loads (from 0 to 500 mg/L) were assessed as proof-of principle in isotonic solution followed by the evaluation of organic matter effect in simulated and actual urban wastewater (UWW), using bare TiO2-P25 as reference. The order of photocatalysts efficiency for both bacterial and CECs removal was: ZnO-Ce congruent to TiO2-P25 > ZnO-Yb > ZnO-Fe > photolysis > darkness in all water matrices. The best photocatalytic performance for water disinfection and decontamination was obtained with 500 mg/L of ZnO-Ce: 80% of Sigma CECs removal after 45 min (4.4 kJ/L of accumulated solar UV-A energy (Q(UV))) and the total inactivation of bacteria (Detection Limit of 2 CFU/mL) after 120 min (14 kJ/L of Q(UV)) in UWW. The microbial and CECs abatement mechanism was described based on the generation of hydroxyl radicals, which was experimentally demonstrated for ZnO-Ce. Additionally, no significant release of Zn2+ and Ce was detected after the solar exposure. These results point out for the first time the capability of ZnO-Ce for the simultaneous UWW disinfection and decontamination under natural sunlight.