(128c) Removal of Nanoparticles Via Coagulation Followed by Sedimentation

Discharge of engineered nanomaterials (ENMs) into freshwater and marine ecosystems is expected to increase with accelerating development of the nanotechnology industry. Studies of the potential environmental and human health impacts of ENMs are in their infancy and information on their removal from nanoparticle laden water streams is scarce. Given that recent studies have shown that nanoparticles can be toxic to single cell organisms, it is imperative that effective methods for the removal of nanoparticles from aqueous systems are identified. Accordingly, the present research focused on evaluating the potential and efficiency of conventional coagulation followed by sedimentation in destabilizing nanoparticles (e.g., TiO2, ZnO, and CeO2) to form aggregates or flocs, and the settlement of these flocs for further separation. A series of experiments with commonly-used coagulants such as aluminum chlorohydrate (ACH), ferric chloride, and polydiallyldimethylammonium chloride (polyDADMAC) were carried out for various coagulant doses, mixing conditions, and sedimentation periods to determine optimal conditions for effective sedimentation of nanoparticles from aqueous solutions. The efficiency of coagulation followed by sedimentation as a first nanoparticle removal was evaluated by measurements of the concentration of nanoparticles (via elemental analysis) in the collected sediment and supernatant phase, in addition to measurements of the particle size distribution via dynamic light scattering for the suspension phase and a coulter counter analysis for the sediment phase. The results indicated that at the optimal conditions, coagulation can lead to the formation of nanoparticle aggregates in the micron size range, thereby suggesting the possibility of using ultra-filtration as a final step for treating the nanoparticle-laden water.