Improving the resistance of Anammox granules to extreme pH shock: The effects of denitrification sludge EPS enhanced by a fluctuating C/N ratio cultivation on granules

This study investigated the effects of denitrification sludge EPS enhanced (DS-EPS CN ) by a fluctuating carbon and nitrogen ratio (C/N) cultivation strategy on the properties of Anammox granules under extreme acid or alkaline shock. The results showed that the DS-EPS CN significantly improved the nitrogen removal performance of low-density Anammox granular sludge (Granules- L ) and high-density Anammox granular sludge (Granules -H ) under extreme acid shock (pH 5.0). The contents of high-molecular-weight substances (such as aromatic proteins and polysaccharides) in the DS-EPS CN rose markedly, contributing to a substantial increase in the flocculation efficiency under acidic conditions and increasing the granule stability. In addition, abundant amounts of N-butyryl- dl -homoserine lactone (C4-HSL) and N-hexanoyl- dl -homoserine lactone (C6-HSL) in the DS-EPS CN promoted the granule activity. However, under extreme alkaline shock (pH 10.5), the flocculation efficiency of the DS-EPS CN was poor, and the addition of DS-EPS CN had no influence on the stability of the granules but improved the activity of the Granules -H . The reason was that the release mechanism of the endogenous acyl-homoserine lactone (AHL) signals in the Granules -H was activated by the exogenous C4-HSL and C6-HSL in the DS-EPS CN under alkaline conditions, leading to increased Granules -H activity. This research provides a novel approach to enhance the resistance of Anammox granular sludge to extreme pH shock. • DS-EPS CN enhanced the property of granules -L and granules -H in extreme acid shock. • DS-EPS CN promoted the activity of granules -H under extreme alkaline shock. • Fluctuating C/N ratio cultivation increased the AHLs content in DS-EPS CN . • Fluctuating C/N ratio cultivation improved the flocculation efficiency of DS-EPS CN .