The preservation of anaerobic ammonium oxidation (anammox) bacteria is a key element in the study and application of the anammox process. Different cryoprotectants (dimethyl sulfoxide and trehalose) at storage temperatures of 4 degrees C and -40 degrees C were selected to construct a preservation system. After 2 months of storage, the performance of the reactors and the particle characteristics from the activity recovery test revealed the advantages and disadvantages of the different storage methods. Ultimately, the preservation method adopted was storage without cryoprotectant at 4 degrees C. With the aid of this optimized method, the nitrogen removal rate reached 4.41 kg m(-3) d(-1) during the recovery period. Among the cryoprotectants assessed, dimethyl sulfoxide was found to be an appropriate cryoprotectant, and trehalose had surprising and unexpected effects. The modified Stover-Kincannon model was suitable for describing the nitrogen removal performance of the reactors with sludge after storage, except for the two reactors in which the granules were exposed to trehalose during the storage period. (C) 2014 Elsevier B.V. All rights reserved.