Temperature dependence of nitrogen removal activity by anammox bacteria enriched at low temperatures.

The anaerobic ammonium oxidation (anammox) process, which is applicable at ambient temperature, is necessary to develop more versatile nitrogen removal technologies. In this study, two anammox reactors, Low-R1 and Low-R2 inoculated with activated sludge respectively in Kumamoto and Hokkaido, Japan, achieved nitrogen removal rates (NRRs) of 1.5 kg-N/m3/day at 20°C. The specific anammox activity (SAA) of the Low-R1 and Low-R2 sludge samples had peaks, respectively, of 2.8±0.3 mg-N/g-VSS/h at 25°C and 4.2±0.3 mg-N/g-VSS/h at 30°C and dropped over the optimum temperature. Moreover, the SAA values of the Low-R1 and Low-R2 were higher at 10-25°C and 10-35°C, respectively, than that of an anammox reactor inoculated with activated sludge in Kumamoto operated at 35°C (Mod-R). The apparent activation energy for anammox of Low-R1, Low-R2, and Mod-R were 108 kJ/mol (10-25°C), 73 kJ/mol (10-30°C), and 89 kJ/mol (10-35°C), respectively. Candidatus Kuenenia stuttgartiensis dominated in the Mod-R sludge. The Low-R1 sludge was comprised of Ca. K. stuttgartiensis, Ca. Brocadia caroliniensis and Ca. B. fulgida and uncultured anammox-like or planctomycete-like bacteria. The Low-R2 sludge was comprised of various uncultured anammox-like or planctomycete-like bacteria. As Low-R2 was constructed, enrichment of freshwater anammox bacteria at low temperature with seed sludge collected from cold regions is expected to be an effective strategy for anammox applications under a wide temperature range.

Simultaneous anammox and denitrification (SAD) process in sequencing batch reactors.

This study investigated nitrogen removal by the simultaneous anaerobic ammonium oxidation (anammox) and heterotrophic denitrification (SAD) process in a sequencing batch reactor (SBR) inoculated with suspended activated sludge and immobilized anammox sludge at various total organic carbon/nitrate (C/N) ratios. Synthetic wastewater containing nitrate 100mg-NL(-1), ammonium 70mg-NL(-1), and acetate 50-250mg-CL(-1) was fed to the SBR. Nitrite reduced from nitrate by heterotrophic denitrification was accumulated and removed with ammonium in each cycle operation of the SBR. The SAD process removed nitrate and ammonium effectively (T-N removal, 58-94%) by the high anammox contribution (ca. 80-100%) under low C/N ratios (0.5-1.0). At high C/N ratios of 1.2-2.5, the SAD process maintained T-N removal 67-79% with predominance of heterotrophic denitrification instead of anammox reaction. Results demonstrated that the SAD process performs high nitrogen removal effectively from wastewater with widely different C/N ratios.