Pharmaceuticals present in sewage may inhibit the biological processes in a sewage treatment plant. In this work, the toxic-effect of six pharmaceuticals (carbamazepine, sulfamethoxazole, propranolol hydrochloride, diclofenac sodium, ofloxacin and clofibric acid) on the anaerobic digestion process is assessed. Acetoclastic methanogenes are the most sensitive group of microorganisms participating in the anaerobic digestion process. Appropriate toxicity tests for these microorganisms were then based on assessing the impact of pharmaceuticals on the specific methanogenic activity (SMA) of the anaerobic biomass. The toxicity was expressed by the IC80 and IC50 values, i.e. the concentration at which bioactivity was 80% and 50% of the control, respectively. Results showed that the pharmaceuticals tested caused a mild inhibition to the methanogenes in most cases, related directly to the tendency of the compounds to adsorb on the anaerobic biomass.

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