A novel kind of biodegradable polymer, i.e., starch/polycaprolactone (SPCL) was prepared and used as carbon source and biofilm support for biological denitrification in a packed-bed bioreactor. The denitrification performances and microbial diversity of biofilm under different operating conditions were investigated. The results showed that the average denitrification rate was 0.64 +/- 0.06 kg N/(m(3) d), and NH3-N formation (below 1 mg/L) was observed during denitrification. The nitrate removal efficiency at 15 degrees C was only 55.06% of that at 25 degrees C. An initial excess release of DOC could be caused by rapid biodegradation of starch in the surfaces of SPCL granules, then it decreased to 10.08 mg/L. The vast majority of species on SPCL biofilm sample (99.71%) belonged to six major phyla: Proteobacteria, Bacteroidetes, Chloroflexi, Firmicutes, Spirochaetes and Actinobacteria. Proteobacteria were the most abundant phylum (85.50%) and mainly consisted of beta-proteobacteria (82.39%). Diaphorobacter and Acidovorax constituted 52.75% of the identified genera which were denitrifying bacteria. (C) 2013 Elsevier B.V. All rights reserved.