Effect of operating conditions and interfering substances on photochemical degradation of a cationic surfactant.

This work investigates the degradation kinetics of a recalcitrant organic pollutant, cetyltrimethylammonium bromide (CTAB), using direct UV and UV-H2 O2 advanced oxidation processes. Direct photolysis at 253.7 nm showed only 55% degradation up to fluence dose of 40.65 J/cm2 for an initial CTAB concentration of 100 mg/L. The apparent fluence-based pseudo-first-order rate constant and quantum yield were 2.29(±0.325) × 10-5  cm2 /mJ and 0.305(±0.043) mol/Einstein, respectively. In case of UV-H2 O2 , >99% degradation was observed up to a fluence dose of 0.79 J/cm2 . The rate constant was ∼200 times higher compared to direct photolysis, which was due to hydroxyl radical generation in the UV-H2 O2 process. The second-order hydroxyl radical rate constant for CTAB was found to be 1.59(±0.18) × 109  M-1  s-1 . The effects of H2 O2 dose, initial CTAB concentration and relevant water quality parameters (pH, alkalinity and nitrate concentrations) were studied; all of these influenced the rate constants. CTAB degradation was also examined in the municipal wastewater matrix. It is concluded that UV-H2 O2 represents an efficient treatment process for CTAB in environmental matrices.