The feasibility of an anammox (anaerobic ammonium oxidation) UASB (upflow anaerobic sludge blanket) bioreactor to treat ammonium-rich brines was investigated in batch and continuous-flow experiments. The evidence from batch tests indicated that the anammox activity was significantly inhibited under highly saline conditions while the inhibition was reversible. Saline shock loading of 30 g NaCl l(-1) caused a 67.5% decrease in specific anammox activity (SAA) compared to reference biomass (not exposed to salt). However, the acclimatized biomass displayed a SAA value just 45.1% lower than that of the reference biomass. When transferred from brine to freshwater, the salt-exposed biomass resumed its activity by 43.1%. Subsequent to appropriate acclimatization, careful manipulation nitrite concentration, nitrogen loading rate (NLR), and other operational parameters for 77 days, the results of continuous-flow experiment revealed that under the salinity of 30 g NaCl l(-1) the reactor performed well and the substrate removal capacity (nitrogen removal rate, NRR, of 448 +/- 15 mgl(-1) d(-1)) was comparable to the condition of freshwater (NRR of 464 +/- 13 mgl(-1) d(-1)). However, the anammox UASB bioreactor was prone to malfunction under transient operating conditions. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.