Biodegradation of ciprofloxacin, sulfamethoxazole, trimethoprim, and tetracycline as a function of microbial growth rate and nitrification
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Two hypotheses were tested to examine biodegradation of ciprofloxacin, sulfamethoxazole, trimethoprim, and tetracycline by suspended growth cultures as a function of microbial growth rate and nitrification. Data for hypotheses testing was obtained from batch biodegradation tests. These tests were performed using four different microbial cultures that were developed in laboratory scale continuous flow completely stirred reactors (CFSTRs) operated under conditions which allowed for selection of cultures with desired characteristics. The influence of microbial growth rate on biodegradation of ciprofloxacin, sulfamethoxazole, trimethoprim, and tetracycline was examined by comparison of antibiotic biodegradation by a low growth rate culture (culture developed in CFSTR operated with mean cell residence time equal to 10 days) to biodegradation by high growth rate culture (mean cell residence time of 2 days) both with minimized nitrification. The effect on nitrification on biodegradation of four antibiotics was evaluated by comparison of three cultures each developed under low growth rate conditions (mean cell residence time equal to 10 day) but with different levels of nitrification. In addition, control reactors were established to account for abiotic removal. The results of hypotheses testing suggest that the biodegradation of ciprofloxacin and tetracycline increases as mean cell residence time decreases. Sulfamethoxazole is biodegraded better by low growth rate cultures as compared to high growth rate cultures. Nitrification was found to positively impact only ciprofloxacin biodegradation. The data obtained for trimethoprim were inconclusive and did not suggest any correlation between trimethoprim removal and microbial growth rate and nitrification.