Comparison of AOPs at pilot scale: energy costs for micro-pollutants oxidation, disinfection by-products formation and pathogens inactivation

Abstract

This work evaluated different advanced oxidation processes (AOPs) operated at pilot-scale as tertiary treatment of municipal wastewater in terms of energy efficiency, disinfection by-products formation and pathogens inactivation. Investigated AOPs included UV/H2O2, UV/Cl2, O3, O3/UV, H2O2/O3/UV, Cl2/O3/UV. AOPs were operated using various ozone doses (1.5-9 mg L-1), and UV fluences (191-981 mJ cm-2). Electrical energy costs necessary for the oxidation of contaminants of emerging concern (CEC) (i.e., carbamazepine, fluoxetine, gemfibrozil, primidone, sulfamethoxazole, trimethoprim) were calculated using the electrical energy per order (EEO) parameter. Ozonation resulted by far the most energy efficient process, whereas UV/H2O2 and UV/Cl2 showed the highest energy costs. Energy costs for AOPs based on the combination of UV and ozone were in the order O3/UV ≈ Cl2/O3/UV > H2O2/O3/UV, and they were significantly lower than energy costs of UV/H2O2 and UV/Cl2 processes. Cl2/O3/UV increased bromate formation, O3/UV and O3 had same levels of bromate formation, whereas H2O2/O3/UV did not form bromate. In addition, UV photolysis resulted an effective treatment for NDMA mitigation even in combination with ozone and chlorine in AOP technologies. Ozonation (doses of 1.5-6 mg L-1) was the least effective process to inactivate somatic coliphages, total coliform, escherichia coli, and enterococci. UV irradiation was able to completely inactivate somatic coliphages, total coliform, escherichia coli at low fluence (191 mJ cm-2), whereas enterococci were UV resistant. AOPs that utilized UV irradiation were the most effective processes for wastewater disinfection resulting in a complete inactivation of selected indicator organisms by low ozone dose (1.5 mg L-1) and UV fluence (191-465 mJ cm-2).