Removal of problematic metals from water via nanoparticle-enhanced membrane filtration

The rising global demand for clean water is challenged by various factors like ever increasing freshwater pollution, more stringent health-based drinking water regulations, and competing demands for clean water from a variety of users. At the same time, the increasing levels of problematic metals in the environment represent a serious threat to human health and ecological systems. Recent advances in nano-scale science and engineering promise solutions to many contemporary water quality and purification issues. Together with membrane separation, selective removal of trace contaminants using functional nanoparticles could be achieved. Nanoparticle enhanced ultrafiltration is a hybrid membrane process, akin to polymer enhanced ultrafiltration, in which target contaminants selectively react with water-soluble nanoparticles and the contaminant-nanoparticle complexes are then removed from water by low pressure membrane filtration. The objective and focus of this study is to demonstrate selective removal and subsequent recovery of target metal ions from complex electrolytes using selective metal-binding nanoparticles that have high binding capacity, could be regenerated and efficiently separated by low-pressure membrane filtration.;In Chapter 1 an extensive literature review on the traditional end novel methods for metal removal from water, together with desired characteristic of the nanoparticle enhanced filtration process is summarized. In Chapter 2, synthesis, physical-chemical properties and metal binding ability of LTA colloidal zeolite crystals is presented. In Chapter 3, the ability of four nano-scale materials to bind cadmium ions, and subsequently, to be removed from water by ultrafiltration was investigated. Kinetic, binding capacity and regeneration of synthesized LTA zeolite, polyacrylic acid, alginic acid and PAMAM dendrimers nanoparticle were tested at various experimental conditions. Separation of nanoparticle metal complexes was investigated using ultrafiltration membranes with various molecular weight cut-off. The focus on Chapter 4 was removal of problematic scaling metal ions from water via nanoparticle enhanced ultrafiltration. The binding kinetics and capacity of LTA zeolite, polyacrylic acid, alginic acid, and PAMAM dendrimers was tested for calcium, barium and strontium in laboratory prepared and natural waters. The influences of solution pH, ionic strength, organic matter and competing divalent cations were investigated for calcium. Finally, a brackish RO brine was "softened" with selected metal binding nanoparticles. The discussion sheds some light on the fundamental physical-chemical mechanisms governing the potential for nanoparticle-enhanced filtration for practical application.