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

The ultraviolet/chlorine (UV/Cl) process is an emerging advanced oxidation technology for micropollutant abatement in water and wastewater treatment. However, the application of the conventional UV/Cl 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/Cl (E-UV/Cl) process for micropollutant abatement under conditions simulating decentralized water treatment. The E-UV/Cl process combines UV irradiation with in situ electrochemical Cl 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/Cl process for water treatment. Due to its multiple mechanisms for micropollutant abatement (direct photolysis, direct electrolysis, Cl-mediated oxidation, as well as hydroxyl radical and reactive chlorine species oxidation), the E-UV/Cl 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/Cl process under similar experimental conditions. The electrical energy per order (E) for micropollutant abatement ranged from 0.15 to 1.8 kWh/m for the E-UV/Cl process, which is generally comparable to that for the conventional UV/Cl process (0.14-2.7 kWh/m). These results suggest that by in-situ generating Cl from anodic oxidation of Cl, the E-UV/Cl process can overcome the barrier of the conventional UV/Cl process and thus provide a promising technology for micropollutant abatement in decentralized water treatment systems.