Understanding Azole Removal: Contribution of Biodegradation and Bioadsorption

Conventional biological treatment in wastewater treatment plants (WWTPs) have demonstrated limited efficiency in removing contaminants of emerging concern. This study investigated the biodegradation of nine azole antifungals using activated sludge from two WWTPs. Nearly complete degradation was observed for ketoconazole (within 17 days) and climbazole (28 days). Clotrimazole and epoxiconazole exhibited notable differences in removal efficiency between two sludges, ranging from 45% to 76% and 50% to 87%, respectively. Moderate removal (39-66%) was observed for tebuconazole, flutriafol, and tiabendazole, while the lowest degradation occurred for imazalil (~ 30%) and fluconazole (~ 10%). Sorption studies revealed that bioadsorption played a major role in the removal of tiabendazole and clotrimazole with 37-40% and 33-38% of the initial amount of compounds adsorbed on activated sludge, respectively. A reduction in microbial metabolic activity and total organic carbon after one week is likely related to substrate depletion typical of batch experiments rather than loss of activated sludge functionality. Transformation product analysis confirmed the formation of several metabolites structurally similar to parent compounds, retaining the bioactive azole ring, with similar or slightly lower toxicity compared to initial azoles. These findings highlight the roles of biodegradation and sorption in the removal of azole fungicides in activated sludge systems and indicate the limited capacity of conventional treatment to fully eliminate these compounds and the potential ecological risks related to the presence of azoles and their degradation products in the environment.