Removal of micropollutants by an electrochemically driven UV/chlorine process for decentralized water treatment

Abstract

The ultraviolet/chlorine (UV/Cl2) process is an emerging advanced oxidation technology for micropollutant abatement in water and wastewater treatment. However, the application of the conventional UV/Cl2 process in decentralized systems is limited by the transport and management of liquid chlorine. To overcome this limitation, this study evaluated an electrochemically driven UV/Cl2 (E-UV/Cl2) process for micropollutant abatement under conditions simulating decentralized water treatment. The E-UV/Cl2 process combines UV irradiation with in situ electrochemical Cl2 production from anodic oxidation of chloride (Cl−) in source waters. The results show that with typical Cl− concentrations present in water sources for decentralized systems (30–300 mg/L Cl−), sufficient amounts of chlorine could be quickly electrochemically produced at the anode to enable E-UV/Cl2 process for water treatment. Due to its multiple mechanisms for micropollutant abatement (direct photolysis, direct electrolysis, Cl2-mediated oxidation, as well as hydroxyl radical and reactive chlorine species oxidation), the E-UV/Cl2 process effectively eliminated all micropollutants (trimethoprim, ciprofloxacin, metoprolol, and carbamazepine) spiked in a surface water in 5 min. In contrast, at least one micropollutant with ∼20–80% residual concentrations could still be detected in the water treated by 10 min of UV irradiation, chlorination, electrolysis, and the conventional UV/Cl2 process under similar experimental conditions. The electrical energy per order (EEO) for micropollutant abatement ranged from 0.15 to 1.8 kWh/m3 for the E-UV/Cl2 process, which is generally comparable to that for the conventional UV/Cl2 process (0.14–2.7 kWh/m3). These results suggest that by in-situ generating Cl2 from anodic oxidation of Cl−, the E-UV/Cl2 process can overcome the barrier of the conventional UV/Cl2 process and thus provide a promising technology for micropollutant abatement in decentralized water treatment systems.