Transformation kinetics of biochemically active compounds in low-pressure UV photolysis and UV/H(2)O(2) advanced...

Factors controlling photolysis and UV/H2O2 photooxidation rates of the biochemically active compounds (BACs) sulfamethoxazole, sulfamethazine, sulfadiazine, trimethoprim, bisphenol A, and diclofenac were determined. Experiments were conducted with a quasi-collimated beam apparatus equipped with low-pressure UV lamps. The effects of pH, H2O2 concentration, and background water matrix (ultrapure water, lake water, wastewater treatment plant effluent) on BAC transformation rates were evaluated. For the sulfa drugs, solution pH affected direct photolysis rates but had little effect on the hydroxyl radical oxidation rate. For sulfamethoxazole, the neutral form photolyzed more easily than the anionic form while the reverse was the case for sulfamethazine and sulfadiazine. For trimethoprim, the hydroxyl radical oxidation rate was higher for the cationic form (pH 3.6) than for the neutral form (pH 7.85). Quantum yields and second order rate constants describing the reaction between the hydroxyl radical and BACs were determined and used together with background water quality data to predict fluence-based BAC transformation rate constants (k'). For both the lake water and wastewater treatment plant effluent matrices, predicted k' values were generally in good agreement with experimentally determined k' values. At typical UV/H2O2 treatment conditions (fluence=540 mJ cm(-2), H2O2 dose=6 mg L(-1)), BAC transformation percentages in North Carolina lake water ranged from 43% for trimethoprim to 98% for diclofenac. In wastewater treatment plant effluent, BAC transformation percentages were lower (31-97%) at the same treatment conditions because the hydroxyl radical scavenging rate was higher.