Efficient Removal of TiO2 Nanoparticles by Enhanced Flocculation-Coagulation

TiO2 nanoparticles (TiO2-NPs) in water were removed by enhanced coagulation with polyaluminum ferric chloride (PAFC) and cationic polyacrylamide (CPAM). The flocculation efficiency by PAFC and PAFC/CPAM for three different initial concentrations (0.2, 2, and 30 mg/L) of TiO2 nanoparticles in pure water and a kaolin suspension system (kaolin concentration: 30 mg/L) were investigated with different coagulant dosages, pH values, precipitation times, and hydraulic conditions. Results showed that the removal rate of TiO2-NPs in the kaolin suspension system was slightly higher than that in a pure water system, and the removal rate of TiO2-NPs obtained by PAFC/CPAM was significantly higher than that by PAFC alone. The removal efficiency of TiO2-NPs increased with increased initial concentration of TiO2-NPs. Under the optimal conditions, the removal rates obtained by PAFC/CPAM for 30 mg/L initial concentration TiO2-NPs in pure water and the kaolin suspension system were 97.98% and 98.62%, respectively. Studies on the fractal dimension of flocs showed that the flocs produced by PAFC/CPAM had a larger fractal dimension than those using PAFC alone. This study demonstrated that turbidity in water helped improve the removal efficiency of TiO2-NPs, and enhanced coagulation can efficiently remove TiO2-NPs from water.