Fate and Removal of Triclosan in Open–water Treatment Wetlands

Triclosan is an antimicrobial agent and one of the many emerging contaminants that is frequently detected in the environment. Triclosan is an endocrine disruptor that is able to accumulate in living organisms (i.e., fish, algae, humans). Triclosan can transform into various transformation products that are potentially toxic and can contribute to bacteria resistance against antibiotics. This research aimed at minimizing the accumulation of toxic by–products in open–water treatment wetlands for the safe transformation of triclosan. This work focused on triclosan phototransformation, and algae uptake and transformation. The results showed that the half–life of triclosan was generally shorter in solutions with a high pH (where the pH is greater than triclosan’s pKa at 8.2), and low dissolved organic carbon (DOC) concentration. However, in treatment wetlands, where the pH is around 7, triclosan phototransformation cannot be maximized unless the DOC is reduced, and the pH is increased. The use of Euglena gracilis strain Z was studied for its potential to (i) provide an additional transformation pathway for triclosan and (ii) naturally increase the pH of the water via photosynthesis. A series of multiple laboratory–scale algae reactors was carried out to investigate triclosan fate in open–water treatment wetlands. The pH of the algae–containing reactors increased during the 25–day experimental period for wetland water, autoclaved wetland water, and growth media. More than 90% triclosan concentration decrease was also observed in the reactors that used continuous (white) light. Data on kinetics, pathway apportionment, and transformation products showed that phototransformation, algae uptake and transformation, microbial transformation, and adsorption (at low pH) all contributed to triclosan elimination in these lab–scale algae reactors. Altogether, these results suggest that triclosan removal can be accomplished with open-water treatment wetlands while minimizing the accumulation of triclosan’s transformation products.Ph.D