Optimizing O₃-UV process for wastewater advanced treatment with a novel mini-fluidic experimental system to minimize...

The ozone-ultraviolet (O₃-UV) process, which has emerged for advanced treatment of the secondary effluents (SEs) of wastewater treatment plants (WWTPs), requires optimization that balances the contributions of O₃ (chemical oxidation) and hydroxyl radicals (HO^•, advanced oxidation) to minimize energy consumption. In this study, a novel bench-scale mini-fluidic O₃-UV system (MFOUS) was developed, allowing for accurate determination and convenient adjustment of the key operational parameters including O₃ mass loading (ML) and UV fluence (F_p). The degradation of refractory organic compounds in the O₃-UV process, expressed by chemical oxygen demand (COD) reduction and biodegradability (i.e., ratio of biological oxygen demand (BOD) to COD) enhancement, was investigated for three typical SEs with different reactivities toward O₃. Moreover, an evaluation method for the energy consumption of the O₃-UV process was established, enabling fine optimization of operational parameters to balance the contributions of O₃ and HO^•. For example, to achieve 40% of COD reduction in SE-1, the ML and F_p should be optimized to 0.340 kg m^-3 and 0.009 einstein m^-2, respectively, resulting in the lowest energy consumption of 7.29 kWh m^-3. Through optimizing the O₃-UV process for energy conservation, this study will help the WWTPs to achieve the energy-neutral goal in the future.