The aim of this work was to compare denitrification activity of three types of encapsulated biomass containing pure culture of Paracoccus denitrificans or Pseudomonas fluorescens or mixed culture of psychrophilic denitrifiers cultivated at 5 degrees C from activated sludge. The experiments were held with synthetic wastewater containing 50 mg L(-1) N-NO(3)(-) under the temperature 15, 10.8 and 5 degrees C. Specific denitrification rates related to the weight of pellets and to the protein content were calculated and the temperature coefficients describing the dependence of denitrification rate on the temperature were determined. Although the mixed culture showed the highest denitrification rate at the temperatures below 10 degrees C, using of pellets containing pure culture is recommended as the mixed culture has slow growth rate and its activity at temperatures above 10 degrees C is very low. (C) 2011 Elsevier Ltd. All rights reserved.