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 associates found that the beads and the bacterial aggregates collided up to a million times more frequently than predicted using the standard "ideal" particle approach.
The Penn State engineer explains that the fact that large aggregates of bacteria and plankton form in the ocean and sink to the sea floor had long been known even though the prevailing theory could not account for the phenomenon. The settling of organic carbon on the ocean floor, in the form of plankton, bacteria and other biological material, is dominated by large aggregate sedimentation. This loss of organic carbon, which is made possible by coagulation, is an important component of maintaining the global atmospheric carbon dioxide balance.
Now, using the new approach developed by Logan, researchers not only can better understand the ocean processes but also can apply the new approach to enhancing coagulation and aggregation in industrial manufacturing or wastewater treatment.
In addition, in studying the ocean processes, Logan has identified a new particle he calls TEP, transparent exopolymer particles. TEP is formed of material made by plankton that helps it to stick together and coagulate. Logan described TEP in a 1993 paper, "The Abundance and Significance of a Class of Large, Transparent Organic Particles in the Ocean," in the journal Deep-Sea Research.
This October, Logan will be honored with the Frontiers in Environmental Research Award of the Association of Environmental Engineers and Science Professors for his work on the formation of fractal particles through aggregation processes.
EDITORS Dr. Logan is at 814-863-7908 or blogan@psu.edu by email.