Deciphering the mechanism of medium size anammox granular sludge driving better nitrogen removal performance

In this study, an integrated investigation to the microbial activities, extracellular polymeric substance (EPS), microbial community and function of anammox granular sludge (AnGS) was performed.Results showed that AnGS at 0.5-1.0 mm had the highest average specific anammox activity (SAA) of 345.9 mg NH₄⁺-N·gVSS^-1·d^-1, but AnGS at 1.0-1.5 mm with higher SAA might lead to better nitrogen removal efficiency. The content of slime EPS and SAA achieved positively correlation with R² of 98.11%, while protein/polysaccharide ratio of slime EPS and sludge volume index achieved negatively correlation with R² of 99.13%. Cadidatus Broccadia and Denitratisoma were positive correlations and most abundant in AnGS 0.5-1.0 mm of 20% and AnGS 1.0-1.5 mm of 37%, respectively. AnGS at 0.5-1.0 mm exhibited higher energy metabolism which mostly contributed to produce protein. The study provides new insights into the mechanisms of AnGS about 1 mm playing more important role in nitrogen removal performance.