Removal of TiO 2 nanoparticles from water by low pressure pilot plant filtration

Abstract Rising use of nanoparticles in manufacturing as well as in commercial products bring issues related to environmental release and human exposure. A large amount of TiO 2 nanoparticles will eventually reach wastewater treatment plants. Low pressure membrane filtration has been suggested as a feasible treatment of water streams. This study investigated first at laboratory scale the influence of: i) membrane material, ii) pore size and iii) water chemistry on nTiO 2 removal. TiO 2 retention was governed by the cake layer formation mechanism and significant retention of nanoparticles was observed even for filters having considerably larger pores than nTiO 2 . PVDF showed a great potential for nTiO 2 rejection. Additionally, filtration pilot plant experiments were carried out using PVDF membranes (0.03 and 0.4 μm pore size). The release of nTiO 2 in the pilot scale filtration system was always above the instrumental detection limit (> 1.5 μg/L) and in most cases below 100 μg/L regardless of the pore size and applied conditions. The nTiO 2 membrane breakthrough predominantly occurred in the first few minutes after backwashes and ceased when the cake layer was formed. Ultrafiltration and microfiltration were comparable with rejection of nTiO 2 above 95% at similar permeate flow rates. Nevertheless, ultrafiltration is more promising than microfiltration because it allowed longer operation times between backwash cycles.