Removal of antibiotics during the anaerobic digestion of slaughterhouse wastewater

Antibiotics and other emerging contaminants are removed by wastewater treatment plants (WWTPs) to a certain extent. However, the removal mechanism is not well understood due to the fact that the majority of the WWTPs only focus on the occurrence of these contaminants in the influents and effluents and sometimes in the sludge. Understanding the removal pathway is therefore difficult. This study is aimed at investigating the removal pathways of selected veterinary antibiotics from wastewater. A laboratory scale upflow anaerobic sludge blanket (UASB) reactor was employed to treat synthetic wastewater to explore the removal efficiencies of five veterinary antibiotics with an initial concentration of 50 µg/L. In a like manner, batch reactors were further used to evaluate the removal routes of the antibiotics. The UASB reactor was operated continuously under mesophilic conditions to evaluate its performance with regards to the removal of organics and at the same time monitor biogas production. Organic loading rate (OLR) was varied from 8 to 9.2 kg.COD.m-3 .d-1while keeping the hydraulic retention time (HRT) constant at 12 h. A COD removal efficiency higher than 75% was achieved at an OLR of 9 kg.COD.m-3 .d-1 , with a HRT of 12 hours. About 80% of the antibiotics were removed during the continuous processes, however, a distinctive pattern of removal was not observed. The kinetic studies using batch reactors showed that the removal route for the antibiotics was majorly adsorption to the sludge. Biodegradation occurred alongside adsorption but to a lesser degree. The kinetic data showed that the antibiotics followed a first order kinetic model with half-lives that ranged from 6 to 77 days.