BACKGROUND: This study investigated the treatment of ampicillin (AMP)-loaded wastewater in airlift reactors where biofilms were developed on granular activated carbon (GAC). A series of batch experiments were thus carried out in order to differentiate potentials of adsorption and biodegradation which would jointly contribute to the AMP removal. RESULTS: Results showed that almost all influent AMP was removed in two reactors supplemented with 4 and 8 mg L-1 AMP, respectively. Batch experiments revealed that the percentage of the AMP removed through biodegradation increased along with the development of biofilms on GAC. For the mature biofilm-covered GAC, adsorption accounted for about 60% of the observed AMP removal, whereas the other 40% could be attributed to biodegradation. Possible degraders of AMP were also identified, such as Acinetobacter sp., Flavobacterium sp., Pseudoxanthomonas sp., Delftia sp. and Sphingobium sp. CONCLUSION: The airlift biofilm reactor with GAC as carrier would be a feasible technology for treating AMP-loaded wastewater due to the joint action of adsorption and biodegradation of AMP by the biofilm-covered GAC. (C) 2010 Society of Chemical Industry