Removal of titanium dioxide nanoparticles from wastewater using traditional chemical coagulants and chitosan

Abstract

AbstractAlum and ferric chloride were used individually as coagulants to remove P25 TiO2 nanoparticles (NPs) from a simulated wastewater. Previous studies have addressed the use of alum, polyaluminum chloride, chitosan, and polyaluminum chloride with chitosan for coagulation of NPs. A goal of this study was to reduce chemical usage associated with wastewater treatment by examining the coagulation effectiveness of chitosan in conjunction with alum. To further reduce chemical consumption during coagulation, the initial solution pH was limited to 6 or 8. A range of alum doses removed NPs from pH 8 wastewater to achieve residual turbidity <1 NTU. NP removal from pH 6 solutions produced water with residual turbidity <2 NTU only at lower initial NP concentrations. For pH 8 solutions, ferric chloride produced treated water with residual turbidity <1 NTU but at higher doses than required for alum. While chitosan alone did not significantly reduce turbidity, the use of alum and chitosan together reduced the optimal alum dose by 10% and also reduced alum treatment acidification. Therefore, the use of chitosan in coagulation can potentially reduce chemical usage during water treatment and the energy and water consumption associated with chemical production. Use of alum with low chitosan concentrations produces faster settling floc, which can potentially reduce settling tank volume and produce an effluent containing lower aluminum concentrations.