Characteristics and mechanism of anammox granular sludge with different granule size in high load and low rising velocity sewage treatment.

• Verified the ideal AnGS size in high load and low rising velocity sewage treatment. • TB-EPS replaced S-EPS as the main component of EPS in large granules. • When the gene copies decrease, the stable flora structure promotes increasing SAA. • PS is related to the formation of AnGS, while PN is the activity improvement. • Granule size >4.75 mm decreased the abundance of functional bacteria. An integrated investigation to structural, activity and microbial diversity of anammox granular sludge (AnGS) in a wastewater treatment system with high ammonia nitrogen load was performed and aimed to establish the relationship between granular size and performance. With the increase in granule size, the main component of extracellular polymeric substances (EPS) changed from slime EPS to tightly-bound EPS, while the organic component remained the same, and the specific anammox activity increased. However, the results of qPCR and high-throughput sequencing showed that for granules with sizes inferior than 4.75 mm, the abundance of ammonia-oxidizing bacteria (AnAOB) increased as the size increased, and the copies of AnAOB decreased when the granule size increased above 4.75 mm, and the community complexity increased. According to the correlation analysis results, AnAOB first accumulated and then optimized the flora structure to improve efficiency and 2.8 mm to 4.75 mm was the optimal size of AnGS. [ABSTRACT FROM AUTHOR]