Modeling and analysis of hydrodynamic and physico-chemical effects in bacterial deposition on surfaces.

The parallel-plate flow chamber (PFC) is often used for characterizing the propensity of microorganisms to attachment to surfaces. The model presented quantitatively analyzes the complex interplay of diffusion, convection, inertial lift, buoyancy, and surface forces in the PFC, which make it difficult to separate the surface- and microorganism-specific effects from the hydrodynamics. An empirical dimensionless factor K entering the boundary condition expresses enhancement of adhesion diffusion of microorganisms across a thin fluid layer adjacent to the surface by adhesion forces. The model examines the role of various factors (e.g., shear rate, size of bacterium, and strength of adhesion) on the rate of bacterial deposition. Using no adjustable parameter for strongly adhesive surfaces and K as the only adjustable parameter for repulsive or weakly adhesive surfaces, the model explains the observed decrease in deposition flux at high flow rates and compares reasonably with reported experimental results. The results suggest that the fitted value of K may be used for 'rating' the propensity of bacteria to deposit on surfaces and separating this from hydrodynamic effects.