Simultaneous nitrogen and carbon removal from swine digester liquor by the Canon process and denitrification

A laboratory-scale completely autotrophic nitrogen removal over nitrite (Canon) biofilm reactor was applied to remove nitrogen and organic carbon from swine digester liquor for 150 d. A stable nitrogen removal rate was reached after a three-week adaptation period. The nitrogen loading rate of influent were 0.20 ± 0.04, 0.26 ± 0.04, 0.26 ± 0.07 kg N m−3 d−1 in period I, II and III, respectively. Nitrogen removal rates reached 0.096, 0.133 and 0.104 kg N m−3 d−1 when the C/N ratios of liquor were maintained at 0.81, 0.65, and 1.24, respectively. The Canon process was better than the denitrification process for nitrogen elimination when the C/N ratio of the influent was controlled below 0.8. PCR-DGGE analysis showed a decrease in microbial diversity of Planctomycetes during long-term operation. In contrast, the aerobic ammonium-oxidizing bacteria species were resistant to the changes due to replacement of synthetic wastewater with swine digester liquor.