Removal of Residual Antibiotics from Aquaculture Effluents by Denitrifying Woodchip Bioreactors

Abstract

The aquaculture industry lacks effective and economical treatment processes to reduce the risk of residual antibiotic residues being discharged into the environment. This study investigated the removal performance of end-of-pipe denitrifying woodchip bioreactors on four commonly used aquaculture antibiotics. Batch experiments were performed to determine the woodchips abiotic adsorption capacity, while continuous-flow tests, and field tests with full-scale woodchip bioreactors, investigated total antibiotics removal from aquaculture effluent. Oxolinic acid showed the highest measured adsorption capacity (21 µg/g), whilst trimethoprim and sulfadiazine were 106 µg/g and 27 µg/g, respectively. In contrast, florfenicol was poorly adsorbed. Further continuous-flow experiments demonstrated the removal of trimethoprim, sulfadiazine, and oxolinic acid as 89, 64, and 63%, respectively, and no significant removal of florfenicol.The greatest change in antibiotics concentrations across all effluent treatment units of a commercial scale aquaculture system was through the woodchip bioreactor, where 77% of trimethoprim and 93% of oxolinic acid was removed. In contrast, sulfadiazine concentration increased by 141% in the woodchip bioreactor due to hydrolysis/deconjugation of its metabolite (acetyl sulfadiazine). Overall, this study demonstrates that end-of-pipe denitrifying woodchip bioreactors can act as barriers to potential discharge of antibiotics from aquaculture, providing substantial reductions in particular for oxolinic acid and trimethoprim.

Keywords: woodchip bioreactor, denitrification, antibiotics, effluent treatment, aquaculture