Potential of titanium coagulants for water and wastewater treatment: Current status and future perspectives

Coagulation is one of the most widely used technologies in water/wastewater treatment. In recent years, titanium (Ti) coagulants have attracted increasing attention due to their outstanding performance and risk-free metal residues in coagulation. Nonetheless, there is a lack of a comprehensive understanding of Ti coagulants from fundamental research to practical application. To provide a full picture of Ti coagulation, the hydrolysis behaviors, coagulation mechanisms, application potential, and economic analysis of Ti coagulants were critically reviewed for the first time in this work. At present, there are three key issues in the development of Ti coagulation: 1) The hydrolysis controllability in the fabrication of pre-polymerized Ti coagulants remains a challenge; 2) New methods for Ti speciation analysis are still highly needed; 3) Scenarios of particular needs for low metal residue or high water clarity are to be found to make a breakthrough in the practical application of Ti coagulants. Cost reduction in the preparation of Ti coagulants and sludge recycling to value-added products are two important measurements to promote the future application of Ti coagulants in water/wastewater treatment. This review offers guidelines for the further research and development of Ti coagulants.