The influence of additives (Ca2+, Al3+, and Fe3+) on the interaction energy and loosely bound extracellular polymeric substances (EPS) of activated sludge and their flocculation mechanisms

► The extended DLVO theory could not explain the AS flocculation with Ca2+ well. ► The AS flocculation with multivalent cations correlated to the LB-EPS content. ► The distribution of Ca2+ in AS was totally different from Al3+ and Fe3+. ► The binding ability governed multivalent cations' influence on AS flocculability.