Indirect photodegradation is a potential attenuation mechanism of emerging contaminants in surface water. The artificial sweetener acesulfame is useful for probing indirect photolysis of contaminants due to its resistance to biodegradation and direct solar photolysis. In this study, indirect photodegradation of acesulfame was investigated under simulated sunlight conditions in synthetic surface water and water from a tropical urban water body. The bimolecular rate constant k’’ for the reaction of hydroxyl radical with acesulfame was determined using competition kinetics to be (4.1±0.59)×109 M-1 s-1 with artificially sunlit hydrogen peroxide as the radical source. The observed rate constant of OH formation from 2mg/L NO2- and NO3- were 3.85×10-6s-1 and 8.95×10-8 s-1 respectively, which indicated that NO2- is 43 times more effective than NO3- for generating OH under the experimental conditions employed. Indirect photolysis was studied under simulated solar irradiation conditions in four surface water samples. The half-life of acesulfame in the surface layer at the four sites ranged from 38h-78h under conditions of maximum daily sunlight near the equator. Kinetic modeling was used to estimate the steady state OH concentration and to evaluate the relative importance of the sensitizing effect of DOC, NO3-, NO2-. Data indicated that DOC was the predominant photosensitizer in the surface water samples contributing &gt; 95% to the degradation with NO3- and NO2- contributing 0.1-1.3% and 1.3–4.4% respectively. The contribution of DOC to the rate of indirect photolysis correlated the light attenuation measured by the absorption of field water at 312nm. Within the DOC range of 2.28-5.05 mgC/L in our field water, the degradation rate was found to be inversely proportional to A312. Considering the strong attenuation of light by DOC, photosensitized degradation appears to be limited to surface layer.

Assessing the indirect photodegradation potential of emerging contaminants in tropical urban surface water using the artificial sweetener acesulfame as a probe

251st National Meeting (2016)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.