Adsorption, inhibition, and biotransformation of ciprofloxacin under aerobic conditions

•Ciprofloxacin (CIP) degraded in a poultry litter extract-fed aerobic culture.•Aerobic culture was inhibited by CIP at 10mg/L or higher.•The degree of inhibition increased with increasing CIP concentration.•A CIP biotransformation product was proposed based on HPLC/UV/MS analysis.•The antibiotic quinolone moiety in CIP was not transformed under aerobic conditions. The adsorption, inhibition, and biotransformation of the fluoroquinolone antibiotic ciprofloxacin (CIP) under aerobic conditions were investigated in this study. The maximum adsorption capacity and the Langmuir constant were 37.9mgCIP/gVSS and 37L/g, respectively. A glucose-fed aerobic culture was inhibited by CIP at 10mg/L or higher and the degree of inhibition increased with increasing CIP concentration. However, the microbial activity recovered to some extent with prolonged incubation under a semi-continuous feeding mode. A low extent of CIP biotransformation was observed in an aerobic, glucose-fed culture derived from poultry litter extract. LC/UV/MS analysis of the biotransformation product showed that only the piperazine ring was oxidized, while the antibiotic quinolone part of CIP was intact.