Using new ways to analyze and describe the rate at which minute ocean-going groups of bacteria or plankton coagulate, a Penn State engineer has found that large aggregates of these groups collide with and capture additional particles millions of times faster than predicted by existing theories.

Dr. Bruce E. Logan, the Kappe professor of environmental engineering, says, "Our results have caused us and many other scientists and engineers to think completely differently about how biological aggregates form in aqueous systems. Such coagulation processes are important in wastewater treatment and industrial manufacturing as well as the ocean and other natural water systems."

Logan is the first to apply the use of fractal geometry to aqueous biological aggregates. Objects arranged in fractal patterns, a snowflake, for example, often look "lacy" and every unit or fragment of it looks like the whole.

Previous methods for describing and predicting the dimensions of biological aggregates have been based on the analysis of single "ideal" particles such as a sphere. However, Logan points out that most real aggregates of interest form particles that have a variety of sizes and shapes. In order to analyze average properties of real aggregates, Logan and his research group have developed new techniques to estimate fractal dimensions and calculate the collision efficiencies between the fractal aggregate and new adhering particles.

Logan will describe the new techniques and calculations at the national meeting of the American Chemical Society in Washington, D. C. on Sunday, August 20. His keynote lecture is entitled, "Fractal Coagulation Processes.

In his experiments, Logan added fluorescent beads to water already containing bacterial aggregates. The coagulation rate, or the rate at which the beads attached to the bacterial aggregates, was calculated by using a microscope to observe and count them over time. He and his research associat
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Contact: Barbara Hale
bah@psu.edu
814-865-9481
Penn State
19-Aug-2000