Collaborative Research: Shape Effects on Microorganism Removal by Microfiltration and Ultrafiltration Membranes

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This NSF award by the Chemical and Biological Separations program supports work to examine from both experimental and theoretical viewpoints the effect of microorganism size and shape on membrane rejection. Microfiltration and ultrafiltration membranes are increasingly employed in the food processing, biotechnology, pharmaceutical industries and for environmental separations. These advanced filtration techniques have gained popularity in municipal water and wastewater treatment particularly following the 1993 Cryptosporidium outbreak in Milwaukee, WI. This is the single largest waterborne disease outbreak in the history of the United States resulting in over 400,000 becoming ill and 50 deaths. Even though membranes present a virtually complete barrier to this parasite (conventional filtration techniques do not), viruses and bacteria can pass through them potentially posing human health risks. MF and UF systems are also employed during purification and manufacturing of drugs, juices, milk and other products where sterility is an important consideration. Paradoxically, even though microfiltration and ultrafiltration systems do not generally achieve complete virus and bacteria removal, the factors governing microorganism transport across them are not well understood, particularly for non-spherical organisms. This necessitates conservative membrane design and implementation. Further, previous experimental and theoretical studies of colloid passage across membranes have focused predominantly on spherical particles even though rod-shaped bacteria and non-spherical viruses are frequently encountered in water supplies. In this work comprehensive theoretical and experimental investigations will be performed to delineate hindered transport phenomena contributing to the removal of viruses and bacteria by microfiltration and ultrafiltration membranes. The focus will be on systematically and rigorously determining the influence of microorganism aspect ratio and the importance of axial and rotational Peclet numbers on transport. The filtration of numerous rod-shaped viruses and bacteria across a range of pore sizes and transmembrane pressures will be examined using both track-etched membranes with an idealized pore geometry as well as commercially relevant phase inversion membranes which have a complex porous structure. A rigorous model that incorporates Brownian diffusion and particle alignment with the flow will be developed. Broader impacts of the work lie in (i) training a high school science/math teacher in Clarkson and another at Houston, (ii) communications with industrial scientists at Millipore Corporation, (iii) training students to perform interdisciplinary and collaborative research applying principles from transport phenomena, biotechnology, and environmental engineering, (iv) supporting undergraduates to conduct research through course projects and summer research, and (v) disseminating research results in peer-reviewed publications and conference presentations. We hope to draw participants from a variety of K-12 institutions across Houston and Potsdam, particularly those with historically minority student bodies in several of these activities.