ABSTRACT
Poly-aluminum chlorides (PACls) of the form AlnCl(3n−m)OHm are typically used as coagulants in water and wastewater treatment to remove dissolved organic compounds and suspended colloidal particles. The efciency of the coagulation process depends largely on the highly efcient occulant, matching reactor (occulator), and auto-dosing control technique (as in the FRD system suggested in the early 1990s; Tang, 1998) besides the source water quality. Among the inuencing factors, the deciding one is the physicochemical properties and the speciation distribution of the coagulant. Traditionally, the most widely applied coagulants are alum and ferric chloride. However, inorganic polymer occulants (IPFs) developed based on the salts in the 1960s are typically applied instead because of their high efciency with relatively low cost, as well as other merits such as tight oc formation, efcient sediment quality and suitability at low temperature, high natural organic matter, wider alkalinity region, etc. (Bottero et al., 1987; Hu et al., 2006; Tang and Luan, 1996; Tang, 1998; Van Benschoten and Edzwald, 1990; Wang et al., 2002; Zhao et al., 2013). Therefore, IPFs could be regarded as second-generation coagulants.
