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Abstract
Discharge of treated municipal effluents is an important route for the release of antibiotic pharmaceuticals into the aquatic environment. The occurrence of antibiotics in the environments is of concern due to their potential impact on aquatic species and the possible proliferation of antibiotic resistant strains of bacteria. Although conventional wastewater treatment processes were not designed to eliminate trace chemical contaminants including antibiotics, selection of appropriate treatment processes and optimization of their operational conditions may enhance the removal of many of these substances.
A highly sensitive and reliable method using liquid chromatography tandem mass spectrometry was developed for the analysis of six sulfonamide antibiotics (sulfadiazine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfapyridine and sulfathiazole), two sulfonamide metabolites (N4-acetyl sulfamethazine and N4-acetyl sulfamethoxazole) and the commonly co-applied antibiotic trimethoprim, in aqueous and solid phases of wastewater. The complex wastewater matrices were shown to result in significant and unpredictable signal suppression for the analysis. Correction of such matrix effects was essential in order to achieve accurate quantification, and this was achieved using isotope dilution.
Several experiments using controlled laboratory treatment processes were conducted to understand the fundamental removal mechanisms of the selected sulfonamide and trimethoprim antibiotics during biological treatment process. Further laboratory experiments were undertaken to assess the effects of specific design and operational parameters on the removal efficiencies of these antibiotics. Case studies at two full scale wastewater treatment plants were also carried out to confirm the removal trends observed in the lab-scale experiments.
Biodegradation was revealed to be the key mechanism for eliminating sulfonamides and trimethoprim during aerobic biological treatment process compared to relatively insignificant removal by sorption to sludge. The removals of sulfonamides by aerobic bioreactors were shown to be consistently greater than that of trimethoprim. During biological treatment, evidence of transformation between sulfonamides and their corresponding N4-acetyl metabolites was observed.
The removals of the investigated antibiotics by membrane bioreactors (MBRs) were shown to be as effective as conventional activated sludge treatment. Furthermore, the effective treatment by MBR was shown to be highly robust and stable over a range of operational conditions. These results reveal MBRs to be an effective technology for biological wastewater treatment and a promising alternative to conventional activated sludge treatment.