The presence of divalent metal ions, such as Ca2+and Mg2+, is an important factor that reinforces the granulation through the strong effect of the ions on the self-immobilization of microbial biomass during start-up aerobic granulation. EPSs would rather bind with multi valent metals to form stable complexes; e.g., Ca2+affects thephysical characteristics of aerobic granules, while the addition of Mg2+ increases microbial diversity in mature granules