The presence of divalent metal ions, such as Ca2+and Mg2+, is animportant factor that reinforces the granulation through the strongeffect of the ions on the self-immobilization of microbial biomassduring start-up aerobic granulation. EPSs would rather bind withmultivalent metals to form stable complexes; e.g., Ca2+affects thephysical characteristics of aerobic granules, while the addition ofMg2+increases microbial diversity in mature granules [15,16].