Removal of ibuprofen and its transformation products: experimental and simulation studies

Pharmaceutically active compounds (PhACs) deserve attention because of their effect on ecosystems and human health, as well as their continuous introduction into the aquatic environment. Classification schemes are suggested to characterise their biological degradation, e.g., based on pseudo-first-order kinetics, but these schemes can vary significantly, presumably due to pharmaceutical loads, sludge characteristics and experimental conditions. Degradation data for PhAC transformation products (TPs) are largely lacking. The present work focuses not only on the biodegradation of the pharmaceutical compound ibuprofen but also on its best-known TPs (i.e., carboxyl ibuprofen and both hydroxyl ibuprofen isomers). Ibuprofen is one of the most commonly consumed PhACs and can be found in different environmental compartments. The experiment performed consisted of a set of aerated batch tests with different suspended solid and ibuprofen concentrations to determine the influence of these parameters on the calculated biodegradation constant (K(biol)). Sampling of the liquid phase at different scheduled times was assessed, removal efficiencies were calculated and pseudo-first-order kinetics were adjusted to obtain experimental K(biol) values for the parent compound and its TPs. The experimental data were successfully fitted to ASM-based models, with K(biol) values for the target compounds ranging from almost 1 to 17 L gSST(-1) d(-1), depending on the concentrations of the biomass and ibuprofen. This work provides innovative knowledge not only regarding the removal of TPs but also the formation kinetics of these TPs.