Physiological and kinetic evaluation of ampicillin oxidation as unique electron source by a denitrifying sludge

BACKGROUND Denitrification allows the simultaneous oxidation of recalcitrant compounds and the reduction of nitrate. Scarce information on consumption and oxidation of ampicillin (AMP) as sole electron source is found in the literature. The physiological and kinetic ability of a denitrifying sludge without previous exposure to antibiotics for oxidizing several AMP concentrations was evaluated. RESULTS Complete denitrification was accomplished in batch reference assays with acetate (20-100 mg C L-1) and nitrate (C/N 1.1) within 4 h of culture, resulting in yields of HCO3- (YHCO3-) and N-2 (Y-N2) of 0.89-1.0 mg C or N produced mg(-1) C or N consumed, respectively. Assays amended with different concentrations of AMP (5-100 mg C L-1) as unique electron source at stoichiometric C/N ratio (0.86) showed that within 8-12 h of culture the antibiotic was totally consumed and oxidized to HCO3- and CO2 (YHCO3- between 0.27 and 0.67 and Y-CO2 between 0.35 and 0.54 mg C produced mg(-1) C consumed), while nitrate was mostly reduced to N-2 (Y-N2 = 0.77-1.0 mg N produced mg(-1) N consumed). At AMP concentrations higher than 20 mg C L-1, N2O and carbon intermediates production was detected. Decreases of 20-90% in denitrifying specific rates were determined regarding the denitrifying reference. After exposure to the antibiotic, the sludge was able to recover its denitrifying activity in the absence of AMP with no N2O accumulation, whereas only 39% of the denitrification rates were recuperated. CONCLUSION It was clearly evidenced that AMP was used as electron donor for conducting denitrification; however, the denitrifying process occurred at lower specific rates. (c) 2021 Society of Chemical Industry (SCI).