Although the use of aluminum salts for water treatment dates back centuries, there have been disputes over the past two decades on the possible adverse effects of aluminum on human health and the environment (WHO, 1997). People are seeking new materials for water treatment to meet increasingly stringent guidelines which require efficient removal of pollutants from water.
Titanium salts used as a chemical for water treatment was first proposed by Upton and Buswell (1937). They reported that coagulation could be effected by dosing titanium sulfate, which flocculated easily at low temperatures and was more efficient for color removal, as compared with alum. For a long time however, probably because of the price of titanium salts, this potential coagulant has been overlooked. Recently, people seem to have a renewed interest in titanium salt for water treatment. Shon et al., 2007 and Shon et al., 2009 experimented with titanium tetrachloride (TiCl4) to flocculate a synthetic sewage and they proposed to recover the widely used titanium dioxide (TiO2) from the settled flocs. Okour et al. (2009a,b) also used TiCl4 and titanium sulfate to treat a synthetic sewage. They reported greater reductions in turbidity, UV254 absorbance and DOC, as compared with the treatment using ferric chloride and aluminum sulfate (Al2(SO4)3). Zhao et al. (2011a) used reservoir water to compare the coagulation effect of TiCl4 with that of poly-aluminum chloride (PAC). They also used synthetic water in other experiments (2011b) to compare the treatment results of TiCl4 with aluminum and iron salts. All these experiments confirmed the flocculation ability of titanium salts. However, the effective pH environment of titanium flocculation was not clearly defined.