Impact of sodium ion on multivalent metal ion content in extracellular polymeric substances of granular sludge from an expanded granular sludge bed.

The long-term and short-term effects of salinity on the multivalent metal ions within extracellular polymeric substance (EPS) were investigated in this study. The results indicated that the Na+ content within the EPS increased significantly from 19.53% to 60.86% under high salinity, and this content in the saline system was 2.2 times higher than that of the control system at the end of the operation. The K+, Ca2+ and Mg2+ contents within the EPS decreased from 33.85%, 39.19% and 5.54% to 7.07%, 25.64% and 3.28%, respectively, when the salinity was increased from 0 g/L to 30 g/L. These ions were replaced by Na+ through ion exchange and competing ionic binding sites under salt stress. The interaction between divalent metal ions and Na+ was reversible with the adaption of anammox to salinity. Salinity exhibited a limited influence on the Fe3+ within the EPS. Sludge granulation was inhibited under conditions of high salinity due to the replacement of multivalent metal ions by Na+.