Photo-assisted electrochemical treatment of municipal wastewater reverse osmosis concentrate

• Organics in RO concentrate were treated by a hybrid advanced oxidation process.
• Hybrid photolytic and electrochemical process showed synergistic DOC degradation.
• Electrochemical breaks down fluorescence and photolysis destroys core structure.
• Hybrid treatment consumes less energy than photolysis alone.

The combination of a photochemical (UV) and electrochemical (EL) process led to enhanced degradation of dissolved organic matter in reverse osmosis (RO) concentrate produced from municipal wastewater. Treatment by UV and EL alone resulted in 25% and 35% removal of dissolved organic carbon (DOC) after 5 h, respectively. However, the hybrid process (UVEL) degraded more than 80% of DOC after the same treatment time. Fluorescence excitation–emission matrix spectroscopy and size exclusion chromatography suggest simultaneous and cooperative degradation of backbone aliphatic bonds by UV and aromatic ring cleavage by EL within the UVEL process. Overall, UVEL treatment led to efficient and non-selective degradation of dissolved organics over a wide range of molecular weights. Further, energy consumption and halogenated by-product formation (typically a limiting factor for the application of oxidation technology) were reduced in the UVEL process relative to the UV and EL processes, respectively.