ABSTRACT
Background: the purpose of this study was to evaluate the influence of different concentrations of erythromycin on the anaerobic treatment of a synthetic pharmaceutical wastewater in an Anaerobic Sequencing Batch Reactor [ASBR]
Methods: a laboratory-scale ASBR was used to treat a synthetic substrate mixture representing pharmaceutical wastewater. The ASBR was operated with increasing organic loading rates until stable removal efficiencies were reached at a loading rate of 3 g COD L-1 d-1. At that point the reactor was exposed to low [1 mg/l] and subsequently, to high [200 mg/l] concentrations of the antibiotic erythromycin
Results: the effect of addition of erythromycin on the microbial community and the development of antibiotic resistance were evaluated based on overall reactor performance and using specific methanogenic activity [SMA] tests. It was found that the addition of erythromycin resulted in a reduction of biogas production and COD removal efficiency by 5 to 10%. As expected based on the reactor performance, biogas. production in SMA tests using the synthetic substrate mixture was only slightly affected by the presence of erythromycin. When sludge from ASBR that had been exposed to erythromycin for 47 days was used for SMA tests, the concentration of butyric acid was inhibited to a lesser extent
Conclusion: the reduction of 5 to 10% in biogas production and COD removal efficiency indicate that a substantial fraction of the microbial populations in the ASBR was resistant to the antibiotic. The conversion of butyric acid was inhibited when erythromycin was present, suggesting that fatty acid-beta oxidizing bacteria were sensitive to the antibiotic