Prediction of chlortetracycline and its transformation products concentrations in anaerobic digestate of swine manure incorporating equilibrium and kinetics

Both veterinary antibiotics and their transformation products threaten the resilience of microbial communities in the environment. This study aimed to evaluate the equilibrium and kinetics of the epimerization and isomerization of chlortetracycline (CTC) antibiotics in swine manure and its anaerobic digestate. Transformation of CTC was conducted in five media (DI water, swine manure, anaerobic digestate, autoclaved anaerobic digestate, filtered-autoclaved anaerobic digestate). The transformation of CTC into epi-CTC (ECTC), epi-iso-CTC (EICTC), and iso-CTC (ICEC) in anaerobic digestion at 35℃ reached equilibrium after 180 hours. CTC, ECTC+EICTC, and ICTC accounted for 25, 20, and 55% (w/w), respectively. The kinetics of degradation, epimerization, and isomerization were interpreted separately using ordinary differential equations based on first-order kinetics. The residual concentrations of CTC, ECTC+EICTC, and ICTC in an anaerobic digester treating swine manure with an initial CTC concentration of 2.20 mg-CTC/L were estimated to be in the ranges of 0.08–1.30, 0.10–1.50, and 0.08–1.25 mg/L, respectively. The analytical solution of the model can be utilized to predict the fate of CTC in the anaerobic digestion of swine manure. • CTC and transformation products were monitored in swine manure and AD-digestate • Equilibrium between chlortetracycline and transformation products reached after 180 h • The 1 st -order kinetic model distinguished degradation and transformation of CTC • The predicted concentrations of CTC in AD plant are 0.08–1.50 mg/L