BACKGROUND: The antibiotics in industrial and munipical wastewaters could not be removed effectively in conventional anaerobic and aerobic biological treatment plants. Few studies have been performed to investigate the biodegradation and inhibition kinetics of oxytetracycline (OTC) on methanogens and total volatile fatty acids (TVFA). RESULTS: A high rate anaerobic multichamber bed reactor (AMCBR) was effective in removing the molasses-chemical oxygen demand (COD), and the OTC antibiotic with yields as high as 96% at an influent OTC loading rate of 133.33 gOTC m-3 day-1 at a hydraulic retention time (HRT) of 2.25 days. Increasing the OTC loading rates from 22.22 gOTC m-3 day-1 to 133.33 gOTC m-3 day-1 improved both hydrolysis and specific utilization of molasses-COD. The inhibition constants of TVFA (KI-TVFA-meth) and OTC (KI-OTC-meth) on methanogens decreased at OTC loadings > 133.33 gOTC m-3 day-1. The direct effect of OTC loadings > 133.3 gOTC m-3 day-1 on acidogens and methanogens was evaluated using the Haldane inhibition kinetic. CONCLUSION: OTC antibiotic was effectively removed in a sequential AMCBR/completely stirred tank reactor (CSTR). The Haldane inhibition constant (KID) decreased significantly at high OTC loads indicating the increase in toxicity. Copyright (c) 2012 Society of Chemical Industry