Long-term effects of N-acyl-homoserine lactone-based quorum sensing on the characteristics of ANAMMOX granules in high-loaded reactors

Abstract Laboratory experiments were carried out to determine the long-term effects of N-acyl-homoserine lactone (AHL)-based quorum sensing on the characteristics of ANAMMOX granules in high-loaded reactors. Results clearly showed that adding 30 mg L −1 N-octanoyl-DL-homoserinelactone (C 8 -HSL) at the initial stage (1–40 d) of the experiment had long-term positive effects on the settleability of granules and controlled the sludge floatation effectively. C 8 -HSL decreased the content of bound extracellular polymeric substances (B-EPS) and the ratio of protein to carbohydrate (PN/PS) by 17% and 48%, respectively and increased the relative hydrophobicity (RH) of the granules by 28%. The results of batch tests indicated that C 8 -HSL significantly reduced the content of loosely-bound EPS (LB-EPS) in the B-EPS, which was responsible for variations in granule settleability and stability. Thus, the settleability of the granules was improved significantly due to addition of C 8 -HSL, contributing to operational stability and the high TN removal efficiency of the reactor. On day 150, when the nitrogen loading rates of all reactors were 13.4 kg TN m −3 d −1 , the nitrogen removal rate and nitrogen removal efficiency of the reactor with C 8 -HSL (R3) were up to 11.2 kg TN m −3 d −1 and 88%, respectively. N-hexanoyl-DL-homoserine lactone (C 6 -HSL) improved activity of the granules, while N-dodecanoyl-DL-homoserine lactone (C 12 -HSL) had no effect on the characteristics of the granules. The long-term effects of C 8 -HSL on the settleability of granules may be attributed to sustainable release of endogenous signals induced by exogenous signal.