The performance of the ANAMMOX process was investigated in two identical laboratory-scale multi- and single-fed upflow anaerobic sludge blanket (UASB) reactors (denoted R-1 and R-0) at different hydraulic residence times (HRTs) varying from 2.06 to 1.52 h and NH4+-N-inf concentrations ranging from 70 to 266 mg L-1. The substrate removal efficiencies of both reactors decreased as HRT decreased and NH4+-N-inf increased. The kinetics of these reactions were analyzed, and the Stover-Kincannon model was appropriate to describe the process kinetics of the reactors. In addition, an empirical model incorporating the influent substrate concentration and HRT adequately described R-1. Shock experiments were conducted in which the reactors were subjected to transient shock loads. The results showed that the operation of R-1 was more stable than that of R-0, especially in response to the substrate shocks. Subsequently, the properties of the ANAMMOX granules and the effects of the feeding protocol on those properties were investigated. (C) 2013 Elsevier Ltd. All rights reserved.