TCAA degradation in ultraviolet (UV) irradiation/hydrogen peroxide (H₂O₂)/micro-aeration (MCA) combination process

The photochemical degradation of trichloroacetic acid (TCAA) employing ultraviolet (UV) irradiation/hydrogen peroxide (H₂O₂)/micro-aeration (MCA) combination process was investigated by varying operational parameters. Relatively slow TCAA degradation was observed during direct UV radiation and H₂O₂ oxidation, while TCAA cannot be removed by MCA alone. UV/H₂O₂/MCA combination process proved to be more effective than UV/H₂O₂. With the initial concentration of 55.7 μg l⁻¹, more than 93.4% of TCAA can be removed within 180 min under UV radiation intensity of 1,048.7 μW cm⁻², H₂O₂ dosage of 30 mg l⁻¹ and MCA flow rate of 25 l min⁻¹ in neutral conditions. Removal rate of TCAA was sensitive to UV radiation intensity, H₂O₂ dose and solution pH, but appeared to be slightly influenced by initial TCAA concentration. There was a higher correlation between pseudo-first rate constant k and UV intensity and H₂O₂ dosage, implying that higher removal capacity can be achieved by improvement of both factors. The newly found trichloroacetamide (TCAcAm), the potential TCAA, was more frangible than TCAA, indicating that TCAA hardly regenerates by hydrolysis of TCAcAm. Finally, a preliminary cost analysis revealed that the UV/H₂O₂/MCA process was more cost-effective than the UV/H₂O₂ process in removal of TCAA from drinking water.