Biodegradation of five pharmaceuticals: estimation by predictive models and comparison with activated sludge data

This study investigated the biodegradation potential of five pharmaceutical micropollutants, acetaminophen, ibuprofen, carbamazepine, sulfamethoxazole and erythromycin, under aerobic conditions. First, theoretical aerobic biodegradation potential of these pharmaceuticals was investigated using the BIOWIN models of the Estimation Programs Interface Suite. The results were then compared with data from activated sludge experiments. The main novelty of this work was that it showed why deviations occurred between theoretical and experimental results. For example, erythromycin was found as the least biodegradable compound in BIOWIN models. On the other hand, carbamazepine proved to be the least biodegradable under experimental conditions. To explain such deviations, biodegradation mechanisms, biodegradation rates and biosorption of pharmaceuticals were taken into consideration. One reason for deviation is that the predictive BIOWIN models consider the single pharmaceutical and relate biodegradability to molecular structure alone. These two points often lead to underestimation of biodegradation. On the other hand, the present study revealed that biodegradation of pharmaceuticals can be enhanced under the microbial and operating conditions of an activated sludge system. Pharmaceuticals can be used as secondary substrates if biodegradable substances are present in an activated sludge. More importantly, they can often be used as cometabolites in the presence of nitrifiers. Also, compared to predicted results, a poorer sorption is observed in activated sludge, indicating that these pharmaceuticals would degrade in liquid phase. Databases/predictive tools are very helpful to have an initial idea about biodegradability. But, in estimation of real biodegradability, there is a need to consider the factors highlighted in this work.