Performance of a combination process of UV/H₂O₂/ micro-aeration for oxidation of dichloroacetic acid in drinking water

The decomposition of dichloroacetic acid (DCAA) in water using a UV/H₂O₂/micro-aeration process was investigated in this paper. DCAA cannot be removed by UV radiation, H₂O₂ oxidation or micro-aeration alone, while UV/H₂O₂/micro-aeration combination processes have proved effective and can degrade this compound completely. With initial concentrations of about 110 μg/L, more than 95.1% of DCAA can be removed in 180 min under UV intensity of 1048.7 μW/cm², H₂O₂ dosage of 30 mg/L and micro-aeration flow rate of 2 L/min. However, more than 30 μg/L of DCAA was left after 180 min by UV/H₂O₂ combination process without micro-aeration with the same UV intensity and H₂O₂ dosage. The effects of applied UV radiation intensity, H₂O₂ dose, initial DCAA concentration and pH on the degradation of DCAA have been examined in this study. Degradation mechanisms of DCAA with hydroxyl radical oxidation have been discussed. The removal rate of DCAA was sensitive to operational parameters. There was a linear relationship between rate constant k and UV intensity and initial H₂O₂ concentration, which indicated that a higher removal capacity can be achieved by improvement of both factors. A newly found nitrogenous disinfection by-product (N-DBP)-DCAcAm, which has the potential to form DCAA, was easier to remove than DCAA by UV/H₂O₂ and UV/H₂O₂/micro-aeration processes. Finally, a preliminary cost comparison revealed that the UV/H₂O₂/micro-aeration process was more cost-effective than the UV/H₂O₂ process in the removal of DCAA from drinking water.