[Analysis of Rapid Start-up and Mixed Nutritional Nitrogen Removal Performance of Complete Autotrophic Granular...

A rapid start of the completely autotrophic nitrogen removal over nitrite (CANON) process based on granular sludge and efficient nitrogen removal under mixotrophic conditions are important steps in a continuous flow reactor for CANON engineering applications. In this study, an aged CANON granular sludge was mechanically crushed to 0.3 mm as inoculum in an airlift internal-loop reactor (AIR) to achieve simultaneous COD removal and mixotrophic denitrification of the single-stage granular sludge. The system achieved stable partial nitrification by controlling DO after 26 days of startup. Granulation and anaerobic ammonia oxidation were then promoted by shortening the HRT to increase the ammonia nitrogen load to 5.65 kg ·(m³ ·d)^-1. The total nitrogen removal rate reached 58% on the 68^th day. Subsequently, the C/N ratio of influent was increased from 0 to 0.25 and 0.5, which promoted the synergistic growth of AOB, AMX, and heterotrophic microorganisms. The removal rates of ammonia and total nitrogen were 95% and 85% respectively, and the removal of COD reached approximately 80%. The activity of NOB such as Nitrospira was effectively inhibited as the COD concentration was increased. q(NH₄⁺-N) and q(TN) were stable at 0.4 g ·(g ·h)^-1 and 0.34 g ·(g ·h)^-1, respectively, while q(NO₃^--N) was approximately 0.02 g ·(g ·h)^-1. Microbial diversity was observed using MiSeq high-throughput sequencing. It showed that organic carbon had no significant effect on the abundance of Nitrosomomas and Candidutus_Kuenenia, while increasing the abundance of Candidutus_Brocadia and Denitratisoma in the sludge. This study provides ideas for the rapid start of continuous flow CANON granular sludge process to treat wastewater with low C/N ratio.