Effect of exogenous N-acyl-homoserine lactones on the anammox process at 15 ℃: Nitrogen removal performance, gene expression and metagenomics analysis.

In this study, C6-HSL and C8-HSL were separately introduced into anammox biofilm reactors to facilitate the anammox performance at 15 ℃. After operation 138 d, total nitrogen removal efficiencies in reactors with amendment C6-HSL or C8-HSL at 15 ℃ reached 76.2% and 74.6%, respectively. Content of extracellular polymeric substances increased by 19.8%, 67.7% and 121.2% in control group, C6-HSL and C8-HSL addition group, respectively. Genes associated with nitrogen removal (i.e., hzo, hzsB, nirS, and ccsB) showed higher expression level at amendment C6-HSL or C8-HSL group. Metagenomics analysis found that amendment of C6-HSL or C8-HL resulted in an increased abundance of genes related to the tricarboxylic acid cycle, amino sugar and nucleotide sugar metabolism, and also genes associated with amino acid biosynthesis pathways. Overall, amendment C6-HSL or C8-HSL had been confirmed as the effective method to improve the performance of anammox bioreactor at 15 ℃.