We have recently developed a novel process to overcome the sludge disposal problem through flocculation using Ti-salt which could also economically recover valuable TiO₂ from wastewater. A large amount of TiO₂ doped with carbon (C) and phosphorus (P) (TiO_1.42C_0.44P_0.14) was produced from the wastewater sludge generated by the Ti-salt flocculation. A simple and novel method to synthesise iron-, aluminium- and calcium-doped titanium dioxide (TiO₂) was investigated. Titanium tetrachloride (TiCl₄) was used as a coagulant to remove pollutants (organic matter and phosphorus) from wastewater. The settled Ti-floc (sludge) was incinerated at 600 ˚C. The resultant by-product from the waste sludge was valuable TiO₂. The Ti-salt coagulant was added with FeCl₃, Al₂(SO₄)₃ and Ca(OH)₂ coagulants to dope iron, aluminium and calcium on TiO₂. The effect of iron, aluminium and calcium on TiO₂ was investigated in terms of the physical, chemical and electronic properties of doped TiO₂ nanoparticles. The TiO₂-WO (without any doping materials), Fe/TiO₂, Al/TiO₂ and Ca/TiO₂ exhibited the majority of the anatase phase after 600ºC calcination. The XRD pattern on the Fe/TiO₂ showed some peaks of hematite (α-Fe₂O₃). The majority of acetaldehyde with TiO₂-WO and Ca/TiO₂ was completely removed under UV irradiation within 40 minutes. Al/TiO₂ led to high photoactivity with removal of 90%. However, at high iron concentration (6.5 at.%), acetaldehyde removal by photoactivity under UV irradiation was marginal. Under visible light, the photo-decomposition of acetaldehyde using TiO₂-WO, Fe/TiO₂, Al/TiO₂, Ca/TiO₂ and P-25 was marginal.