Removal of Nanoparticles by Coagulation Integrated with Membrane Filtration

Though it has been claimed that nanotechnology has great potential for cleaner technology, caution is required to avoid the discharge of nanoparticles to the environment. Studies relevant to human exposure have shown that nanoparticles can be hazardous. Manufactured nanoparticles may also have ecotoxicological effects after discharge into water. Given the above concerns, efforts have been devoted in recent years to assess the effectiveness of traditional water treatment process for the effective removal of nanoparticles from wastewater and treatment of water sources for potable use. A number of recent studies have raised concern that traditional water treatment technologies may be of limited effectiveness in capturing nanoparticles. It may be feasible, however, to remove nanoparticles from water systems by coagulation, followed by sedimentation and then membrane filtration (e.g., UF or MF). In the present work, the effectiveness of coagulation of nanoparticles (e.g., consisting of TiO2, ZnO and CeO2) to enable UF/MF filtration removal of nanoparticles was investigated. The impact of nanoparticles (prior to and post coagulation) on membrane fouling was evaluated as a function of solution chemistry (ionic composition and strength) and hydrodynamic conditions in a plate-and-frame filtration system. The effectiveness of nanoparticle coagulation (evaluated for the coagulants aluminum chlorohydrate, ferric chloride, and polydiallyldimethylammonium) was assessed for a coagulant dose ranging from about 1 ppm - 10 ppm. Coagulation followed by sedimentation allowed nanoparticle removal efficiency in the range of 20-60% (by weight), while subsequent membrane filtration enabled greater than 90% removal.