Comparison of UV/H2O2 and UV/PS processes for the treatment of reverse osmosis concentrate from municipal wastewater reclamation

Reverse osmosis concentrate (ROC) from municipal wastewater treatment contains high concentrations of complex toxic biorefractory pollutants. We studied the mechanisms by which two ultraviolet advanced oxidation processes, UV/H2O2 and UV/PS, degraded pollutants in ROC from municipal wastewater reclamation processes. Both technologies had similar removal efficiencies of bulk dissolved organic matter based on the observed reduction in COD, chromophores, and fluorophores. However, UV/PS decomposed both high and medium molecular weight (MW) fractions (57 and 67.7%), while UV/H2O2 preferentially decomposed only the high MW fraction (60 and 39.1%), suggesting that the two methods operate by different reaction mechanisms. The changes in electron donating capacity resulting from treatment by UV/H2O2 (42.3%) and UV/PS (75.2%) were different. SO4 center dot- primarily decomposed compounds containing electron-donating groups better than (OH)-O-center dot. The removal of dissolved organic matter by UV/PS resulted in decreases in both relative electron-donating capacity and relative specific ultraviolet absorbance. The distinct reaction mechanisms were observed between UV/PS and UV/H2O2, being that UV/PS preferentially decomposed the contaminants via electrophilic addition and hydroquinone generation, while UV/H2O2 preferentially decomposed the contaminants via phenolic-ring cleavage reactions. Changes in the UV absorbance (UVA(254)) and the fluorescence index (FI) were used to monitor the rate of elimination of toxic biocides in the ROC.