Evaluation of Titanium Tetrachloride (TiCl₄) as an Alternative Coagulant and Characterization of Recovered TiO₂.

Abstract

Titanium tetrachloride (TiCl₄) as an alternative coagulant to remove organic matters and nutrients from the effluent of the secondary wastewater treatment was evaluated by comparison of removal efficiency of total phosphorous to Al- and Fe-based coagulants. Also, the surface characteristics, elemental contents, and crystallinity of the TiO₂ produced from wastewater sludge flocculated with TiCl₄ coagulant were investigated depending on the calcination temperatures. The more dosages of coagulants were injected, the greater concentrations of the cations (Al+3, Fe+3, Ti+4) and hydrogen ions (H+) resulted in the lower pH. Also, TiCl₄ formed larger and heavier flocs than other coagulants and resulted in greater T-P removal efficiencies with reduced amounts of dosage. The phase change of anatase and rutile crystalline structures of TiO₂ incinerated from wastewater sludges of TiCl₄ coagulant was observed at relatively high calcination temperatures due to the existence of mixtures of organic matters, nutrients, and various impurities in the wastewater sludges of TiCl₄ coagulant. Both C and P atoms were found to be mainly doped in/on TiO₂ and the C and P atom originated from residual carbon of the settled organic matters and phosphorus nutrients present in effluents from sewage treatment plant, respectively. Therefore, 600-800 °C is the optimal calcination temperatures for TiO₂ produced from TiCl₄ coagulant flocculated with effluents from sewage treatment plant.