Sorption and Biodegradation of Pharmaceutical Compounds in Biological Wastewater Treatment Process

Abstract

This study was performed to investigate the removal mechanisms of pharmaceutical compounds (PhACs) in biological treatment processes. The removal efficiencies and byproducts of three model compounds including 17a-ethinylestradiol (EE2), Carbamazepine (CBZ), and Trimethoprim (TMP) were monitored in laboratory scale membrane bioreactor (MBR), sequencing batch reactor (SBR), and conventional bioreactor (CBR). Laboratory scale bioreactors were used to investigate sorption and biodegradation of EE2. Results showed that the sludge taken from the MBR had partitioning coefficient (Kd) that was more than twice that of biomass derived from SBRs. The MBR biomass had smaller particles and was more hydrophobic than the SBR biomass. Experiments with nitrifying sludge showed that sorption was more important when the initial ammonia concentration was 48 mg/L or less, but at higher initial ammonia concentrations the role of biodegradation became more important. The ammonia monooxygenase (AMO) containing protein extract removed EE2 in batch tests. The influence of biomass characteristics on Kd and sorption-hysteresis of EE2 using MBR and SBR was investigated under normal and nutrient deficiency condition at different SRT. Under normal growth condition, the biomass mean particle size had a dramatic effect on Kd and on sorption hysteresis index (HI). The EE2 partitioning coefficient and sorption hysteresis showed the considerable nonlinear relationship with the mean particle size. Visualization study confirmed this phenomenon. Although under nitrogen deficiency condition, Kd and HI had weak correlation with particle size, overall results showed that the magnitude of the Kd and sorption-hysteresis is affected by the particle size. This study also numerically explored the impacts of sorption hysteresis. Batch experiments showed that ring A of EE2 is the site of electrophilic initiating reactions, including conjugation and hydroxylation. Ring A was also cleaved before any of the other rings are broken, which is likely because the Frontier Electron Density (FED) of the ring A carbon units is higher than those of rings B, C, or D. EE2 and NH3 were degraded in the presence of an AMO containing protein extract, and the reaction stoichiometry was consistent with a conceptual model. Continuous tests showed a linear relationship between nitrification and EE2 removal in enriched nitrifying cultures. Removal efficiencies of EE2, CBZ, and TMP were monitored in nitrifying sludge reactor and conventional bioreactor fed with toluene. EE2 was most efficiently removed in both reactors. The prediction tool combined with FED and degradation rules was applied to predict biodegradation reaction. Degradation reaction took place in the high FED region in three model compounds.