Understanding the N-acylated homoserine lactones(AHLs)-based quorum sensing for the stability of aerobic granular sludge in the aspect of substrate hydrolysis enhancement

complex substrate uptake via hydrolysis enhancement and EPS secretion, which together Efficient substrate metabolism is the premise for stable operation of aerobic granular sludge and can be regulated by quorum sensing (QS). In this study, starch and acetate were selected to represent complex and simple substrates to pro-vide comparable amount of metabolic energy for granules cultivation. Starch-fed granules were larger in size and contained higher EPS content than acetate-fed granules, though both granules exhibited similar substrate -degradation rates during sequencing batch reactor (SBR) cycle. Three N-acylhomoserine lactones (AHLs), including C8-HSL, 3OHC8-HSL and 3OHC12-HSL, were detected as dominant autoinducers in granules. They accumulated more in starch-fed granules than acetate-fed granules. The batch experiments were implemented to investigate QS reg-ulation for granular stability in terms of substrate hydrolysis and transformation. The addition of three AHLs increased the activity of alpha-amylase, the main starch hydrolase, 4-6 times, significantly (p < 0.01) higher than the control treat-ment without AHLs amendment. While activity of dehydrogenase, the main simple substrate degradation enzyme, was increased only 1-2 times. Higher enzyme activity, especially alpha-amylase, significantly (p < 0.05) promoted the substrate-degradation rate (65 % than control group) and EPS yield in starch-fed system. Overall, QS can facilitate sludge granulation and stability.

Automated summary

In this study, it was found that starch-fed granules were larger and contained higher EPS content than acetate-fed granules. Three AHLs were detected as dominant autoinducers in the granules, and their addition increased the activity of alpha-amylase, leading to higher substrate-degradation rate and EPS yield in the starch-fed system, thereby promoting the stability of the granules.