Effect of organic carbon on nitrification efficiency and community composition of nitrifying biofilms

The effects of organic carbon/inorganic nitrogen (C/N) ratio on the nitrification processes and the community shifts of nitrifying biofilms were investigated by kinetic comparison and denaturing gradient gel electrophoresis (DGGE) analysis. The results showed that the nitrification rate decreased with an increasing organic concentration. However, the effect became weak when the carbon concentration reached a sufficiently high level. Denitrification was detected after organic carbon was added. The 12 h ammonium removal rate ranged from 85% to 30% at C/N = 0.5, 1, 2, 4, 8, and 16, as compared to the control (C/N = 0). The loss of nitrogen after 24 h at C/N = 0.5, 1, 2, 4, 8, and 16 was 31%, 18%, 24%, 65%, 59%, and 62%, respectively. The sequence analysis of 16S rRNA gene fragments revealed that the dominant populations changed from nitrifying bacteria (Nitrosomonas europaea and Nitrobacter sp.) to denitrifying bacteria (Pseudomonas sp., Acidovorax sp. and Comamonas sp.) with an increasing C/N ratio. Although at high C/N ratio the denitrifying bacteria were the dominant populations, nitrifying bacteria grew simultaneously. Consequently, nitrification process coexisted with denitrification.