Effect of humic acids on the photodegradation of emerging pollutants under UVA-vis irradiation.

ANTONIO ARQUES; LUCIANO CARLOS; DANIEL O. MARTIRE; JUAN GOMIS; ANTONIO BERNABEU

Costa Mesa, California

Simposio; Fourth IWA Specialty Conference Natural Organic Matter: From Source to Tap and Beyond; 2011

The effect of the presence of humic acids on the elimination of a mixture of emerging pollutants commonly present in natural waters has been studied. For this purpose, the chosen pollutants were acetominophene (analgesic), caffeine (stimulating agent), acetemiprid (pesticide), clofibric acid (fungicide), carbamazepine (psychiatric drug) and amoxycilin (antibiotic). Solar irradiation of pollutants could result in a self cleaning of the aquatic systems if the photoproducts are less toxic than the parent compounds. Humic acid might have a remarkable influence in these photochemical processes as they have been reported to generate highly reactive species such as singlet oxygen, hydroxyl radicals and triplet excited states. On the other hand, their presence could result in a screen effect which minimizes direct photolysis of the contaminants. Experiments carried out with simulated sunlight (20 mg/L of humic acids and 5 mg/L of each pollutant) showed that the screen effect was predominant under those conditions, as lower reaction rates were measured in all cases. The decrease in the photodegradation rate was higher for those contaminants which suffered faster photolysis (clofibric acid, acetamiprid and amoxicillin), while it was not so remarkable for those molecules that can be able to react with singlet oxygen (acetominophene and carbamazepine). Experiments carried out with lower concentration of pollutants (50 μg/L) showed that only caffeine and carbamazepine remained in the solution after 4 h of irradiation. TOC analyses showed that the mineralization was lower than 5% after 8 h of irradiation in all cases. Finally, toxicity tests based on the inhibition of the luminescence of V. fischeri indicated that there was a sharp increase of toxicity at the initial steps of the process, which decreased slowly only after longer periods of irradiation.