Advanced treatment of urban wastewater by UV-C/free chlorine process: Micro-pollutants removal and effect of UV-C radiation on trihalomethanes formation.

The effect of the UV-C/free chlorine (FC) process on the removal of contaminants of emerging concern (CECs) from real urban wastewater as well as the effect of UV-C radiation on the formation of trihalomethanes (THMs) compared to FC process alone was investigated. Unlike of FC process, UV-C/FC was really effective in the degradation of the target CECs (carbamazepine (CBZ), diclofenac, sulfamethoxazole and imidacloprid) in real wastewater (87% degradation of total CECs within 60 min, QUVC = 1.33 kJ L-1), being CBZ the most refractory one (49.5%, after 60 min). The UV-C radiation significantly affected the formation of THMs. THMs concentration (mainly chloroform) was lower in UV-C/FC process after 30 min treatment (<1 µgL-1 = limit of quantification (LOQ)) than in FC process in dark (2.3 µgL-1). Noteworthy, while in FC treated wastewater chloroform concentration increased after treatment, UV-C/FC process resulted in a significant decrease (residual concentrations below the LOQ), even after 24 h and 48 h post-treatment incubation. The formation of radicals due to UV-C/FC process can reduce THMs compared to chlorination process, because part of FC reacts with UV-C radiation to form radicals and it is no longer available to form THMs. These results are encouraging in terms of possible use of UV-C/FC process as advanced treatment of urban wastewater even for possible effluent reuse.

Contaminants of emerging concern removal from real wastewater by UV/free chlorine process: A comparison with solar/free chlorine and UV/H2O2 at pilot scale.

The removal of contaminants of emerging concern (CECs) from urban wastewater treatment plants (UWTPs) is really important to minimize the risk for human health and environment. In this study, the homogeneous advanced oxidation process (AOP) UV-C/free chlorine (UV-C/FC) was investigated at pilot scale in the degradation of a mixture of four CECs, in different water matrices and compared to a consolidated AOP, namely UV-C/H2O2. As matter of fact 90% degradation of CECs was observed after 15 min (QUVC = 0.33 kJ L-1) by UV-C/FC (5 mg L-1 of FC) and 30 min (0.67 kJ L-1) by UV-C/H2O2 (5 mg L-1 of H2O2) in natural water. However, CECs degradation by UV-C/H2O2 and UV-C/FC was comparable (>82%) in wastewater samples, under the investigated conditions (60 min, 1.33 kJ L-1). The effect of sunlight/FC process on the target CECs was also investigated (in a compound parabolic collector based reactor). Interestingly, a different behaviour was observed between the two light sources. In particular, a total removal of carbamazepine (CBZ) and imidacloprid (IMD) was observed for UV-C/FC process with 0.27 kJ L-1 and 10 mgL-1 of FC, while, in the sunlight/FC process (same FC dose), CBZ total removal took place quite fast (0.50 kJ L-1), but 90% removal of IMD was observed only after 60 min (7.09 kJ L-1). In conclusion, UV-C/FC process can be an interesting solution for tertiary treatment of urban wastewater for the removal of CECs and sunlight/FC is worthy of further investigation to evaluate its possible application in small UWTPs.