Logan 9708421 The principal investigators and their colleagues undertake a systematic study of nonlinear phenomena in the transport of bacterial and other colloidal substances through domains of variable porosity. They assume that the porosity is a function of the colloid concentration, which places a nonlinearity in the time-derivative term of the resulting reaction-diffusion-convection equations that govern the flow. The investigators address issues of well-posedness and qualitative behavior for some of these types of biofilm problems, using techniques such as energy arguments and semigroup analysis. They also study the existence of traveling wavefronts in these systems using dynamical systems methods. A significant part of their effort is to interact with colleagues in the geosciences in order to be certain that the models they study are physically well-founded. The presence of colloids, of which some bacterial substances are examples, in subsurface aquifer systems can have a profound effect on the transport of contaminants. For example, hydrocarbons can form a substrate for microbial growth which can then result in the formation of a biofilm on the solid surfaces of the aquifer. The behavior of biofilms in important in the mining industry for the leaching of metals from ores, in the petroleum industry for the control of biofilm accumulation to prevent plugging in oil recovery, and especially in the environmental water resources area for in-situ bioremediation. It has been demonstrated experimentally that the presence of bacterial substances can enhance the transport of harmful chemicals, like DDT, through the soil; in other cases, biofilms can form barriers that block the transport of such contaminants. The investigators study mathematical equations that model the interaction of contaminants and colloidal particles and the effects of these interactions on the flow characteristics of subsurface domains. One goal is to understand, through exami ming the validity of various models, how different mechanisms affect the hydrodynamic flow.
