Increasing Carbon to Nitrogen Ratio Promoted Anaerobic Ammonia-Oxidizing Bacterial Enrichment and Advanced Nitrogen Removal in Mainstream Anammox System

The effects of fluctuating organic carbon to nitrogen (C/N) ratios on mainstream simultaneous partial nitrification, anammox, and denitrification (SNAD) process were studied over 376-day period. The nitrogen removal efficiency decreased from 85.0 +/- 6.6 % to 75.8 +/- 2.8 % as C/N ratio decreased (3.4 -> 1.7), but increased to 82.0 +/- 1.9 % when C/N ratio raised to 2.9 and to 78.4 +/- 3.0 % when C/N ratio decreased again (2.9 -> 2.1), indicating that high C/N ratios promoted nitrogen removal. As C/N ratio raised (1.7 -> 2.9), anaerobic ammonia-oxidizing bacteria (AnAOB) abundance increased from 1.3 x 10(9) to 2.0 x 10(9) copies/L, which explained the improved nitrogen removal. With an elevated C/N ratio, partial nitrification and endogenous partial denitrification reactions were enhanced, providing more nitrite for AnAOB. Additionally, the aerobic_chemoheterotrophy function and particle sizes increased, forming more stable anoxic microenvironment for AnAOB. Overall, increasing C/N ratio promoted the stability of mainstream SNAD.