Evaluation of titanium tetrachloride and polytitanium tetrachloride to remove phosphorus from wastewater

Coagulation of titanium tetrachloride (TiCl4) and polytitanium tetrachloride (PTC) was studied at various conditions in treating wastewater that contained phosphorus (P). Jar-test experiments were performed at various chemical doses (0.02-0.49 mM), alkalinities (50 ≤ AT ≤ 150 mg CaCO3/L of NaHCO3), pH levels (3.0-8.5), and OH/Ti ratio (0.3 ≤ B ≤ 3.0) to determine the conditions at which P (2 mg/L) removal was most efficient. The TiCl4 concentration ([TiCl4]) required to achieve 98-99% P removal was 0.25 mM at 50 mg CaCO3/L, 0.31 mM at 100 mg CaCO3/L, and 0.49 mM at 150 mg CaCO3/L. Response surface analysis predicted that P removal would reach 100% at controlled pH = 3.5 with minimum [TiCl4] = 0.21 mM. PTC removed P most effectively at B = 0.3, and the optimal dose at B = 0.3 was 0.27 mM. Laboratory results and a pilot experiment will help to optimize use of Ti-based coagulants to remediate wastewater that contains P.