Basicity of titanium-based coagulants matters in the treatment of low-turbidity water

Basicity is an intrinsic factor of coagulants that plays important roles in turbidity removal. However, the effects of basicity on the coagulation performance of titanium (Ti) coagulants remain unclear. This knowledge gap is mainly due to the lack of highly polymerized Ti coagulants. In this study, we fabricated a series of Ti-based coagulants with basicity values in the range of 0-93% and evaluated their coagulation performance with simulated and real waters of low-turbidity. A positive correlation was observed between the basicity of the Ti coagulants and the coagulation performance, i.e., higher basicity led to higher turbidity removal, larger floc size, and faster settling rate. For the two titanium xerogel coagulants (TXC) of similar chemical structures, the one with a higher basicity (TXC-93%) worked better than the one of a lower basicity (TXC-78%). The advantage brought from the difference in basicity is of great significance in the purification of low-turbidity water. For the treatment of a surface river water, the required dosage of TXC-93% was about 1/2 to 1/3 of those of titanium tetrachloride (TiCl4) and polytitanium tetrachloride (PTC-21%), and was comparable to that of a high-quality commercialized polyaluminum chloride (PAC-72%). The results here provide a useful technical guidance for the mass production and application of Ti coagulants.