Coupling Small-particle Adsorbents with Membranes for Trace-containment Removal in Water Treatment

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CBET 1236070David Ladner, Tanju Karanfil, Thompson MeffordRecent technological advances have resulted in promising nano- and micro-sized (small-particle) materials that can remove synthetic organic chemicals (SOCs) from drinking water. These small-particle adsorbents, such as graphene platelets and super-fine powdered activated carbon (S-PAC), show faster adsorption kinetics than larger materials. Small-particle adsorbents also perform better in the presence of natural organic matter (NOM), which means they may be better in real-world situations. However, a practical problem exists with small particles: preventing their passage into the finished drinking water. Microfiltration (MF) and ultrafiltration (UF) membrane processes can be effective, but pore blockage by the small materials decreases water flux and increases the energy required for separations. Thus there exists a quandary: small particles are best for SOC adsorption, but large particles are easier to remove. A major advancement would be to find materials and conditions where SOC adsorption is high, NOM competition is low, and little energy is required to remove the adsorbents. This project is built around three main Aims: (1) Determine the properties of small-particle adsorbents that enable SOC adsorption with minimal interference by NOM. (2) Determine the extent to which small-particle adsorbents will foul membranes of various pore size and examine the particle breakthrough propensity. (3) Explore engineering methods to achieve SOC adsorption with minimal energy required for membrane separations. In Aim 1 NOM will be extracted from raw water and from coagulated/flocculated water to test competitive adsorption of SOCs. In some experiments 3H-labeled NOM and 14C-labeled atrazine will be used to investigate mass-transport mechanisms. In Aim 2 membrane flux and particle breakthrough will be measured when removing small-particle adsorbents, taking into account the effects of aggregation. Carbon spheres will be produced with well-controlled particle size to carefully study particle size effects. In Aim 3 a reactor/membrane setup will be used that will allow SOC adsorption by dispersed particles before inducing aggregation that is expected to decrease fouling and membrane breakthrough. Adsorption capacity and kinetics are commonly investigated for novel materials, but here both competitive adsorption effects and small-particle removal requirements will be explored simultaneously to learn how these phenomena are interconnected. For example, the structure of an aggregate of small particles will affect both adsorption kinetics and membrane transport. Novel techniques will be used to investigate the phenomena, such as the radiolabeled NOM and atrazine for detection levels that have not previously been achieved in competitive adsorption studies. Further, the concept of induced adsorbent aggregation in membrane systems has not been previously explored.This project may lead to engineered unit processes specifically designed to efficiently remove SOCs of concern, like personal care products and endocrine disrupting compounds, from drinking water sources to protect human health. The study will also elucidate desirable materials properties, giving researchers targets for which they can aim in future materials development. Although SOC removal is the focus, this is in fact a hybrid system that will allow multiple treatment objectives in a single process (i.e., the control of both small molecular weight contaminants and microbial contaminants). Moving into the future, sustainable water treatment will require low-footprint and low-energy processes, which are the dual objectives here.