The adaptation of Anammox (ANaerobic AMMonium OXidation) to low temperatures (10-15 degrees C) is crucial for sustaining energy-efficient nitrogen removal from the mainstream of municipal wastewater. But, current adaptation methods take months or even years. To speed up the adaption of Anammox to low temperatures, this study describes a new approach: exposing Anammox microorganisms to an abrupt temporary reduction of temperature, i.e., cold shock. Anammox biomass in a moving bed biofilm reactor was subjected to three consecutive cold shocks (reduction from 24 +/- 2 to 5.0 +/- 0.2 degrees C), each taking eight hours. Before the cold shocks, Anammox activity determined in ex situ tests using the temperature range of 12.5-19.5 degrees C was 0.005-0.015 kg-N kg-VSS-1 day(-1). Cold shocks increased the activity of Anammox at 10 degrees C to 0.054 kg-N kg-VSS-1 day(-1) after the third shock, which is similar to the highest activities obtained for cold-enriched or adapted Anammox reported in the literature (0.080 kg-N kg-VSS-1 day(-1)). Fluorescence in situ hybridization analysis showed that Ca. Brocadia fulgida was the dominant species. Thus, cold shocks are an intriguing new strategy for the adaptation of Anammox to low temperature. (c) 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:277-281, 2018