© 2014 Published by Elsevier Ltd. The fate of benzotriazole (BTri) and 5-methylbenzotriazole (5-MeBT) was investigated under anaerobic conditions at nano gram per litre concentrations in large-scale laboratory columns to mimic a managed aquifer recharge replenishment strategy in Western Australia. Investigations of BTri and 5-MeBT sorption behaviour demonstrated mobility of the compounds with retardation coefficients of 2.0 and 2.2, respectively. Degradation processes over a period of 220days indicated first order biodegradation of the BTri and 5-MeBT under anaerobic aquifer conditions after a biological lag-time of approximately 30-60days. Biodegradation half-lives of 29±2 and 26±1days for BTri and 5-MeBT were respectively observed, with no threshold effect to biodegradation observed at the 200ngL-1. The detection of degradation products provided further evidence of BTri and 5-MeBT biodegradation. These results suggested that if BTri and 5-MeBT were present in recycled water recharged to the Leederville aquifer, biodegradation during aquifer passage is likely given sufficient aquifer residence times or travel distances between recycled water injection and groundwater extraction.