The purpose of studying the biodegradability of pharmaceutical compounds is to evaluate their behaviors in relation to the treatment processes generally used in domestic and industrial wastewater treatment plants. The antibiotic norfloxacin was found to be a recalcitrant compound. The studies conducted showed norfloxacin removal rates of 12% and 18% when biomasses from treatments with activated sludge and anaerobic biodigesters, respectively, were used without acclimatization. This suggests that anaerobic digestion shows better performance for norfloxacin removal. Ecotoxicological tests, using the luminescent marine bacteria Aliivibrio fischeri as the test organism, show that anaerobic digestion could eliminate the toxicity of the antibiotic norfloxacin, even though total degradation of the drug was not observed. The release of norfloxacin during cell lysis suggests the importance of controlling this phenomenon in biological treatment systems that handle wastewater contaminated with norfloxacin, thus preventing the return of this drug to the environment.