Collision efficiency distribution of a bacterial suspension flowing through porous media and implications for field-scale transport

The collision efficiency (α) distribution of a bacterial population was determined using multiple packed-bed columns of varying lengths and analyzing the bacteria clean-bed breakthrough concentrations using a distributed colloid filtration theory. This technique allows the α distribution to be determined independently from other effects that can cause non-exponential deposition, including detachment and blocking. It was found that multiple probability density functions (PDF's) could accurately replicate the experimental data. Regardless of which PDF was used, a distributed α resulted in significantly greater predicted field-scale transport than when using a single α. However, there were wide variations in the predicted field-scale transport between the different distributions, suggesting that lab-scale experiments may not be readily utilized to determine the specific PDF that best represents α at the field scale. Finally, blocking was observed in the column effluent curves, underscoring the fact that if non-clean-bed processes occur then an approach such as that utilized in the current study may be used to separate the non-clean-bed and clean-bed processes when determining the collision efficiency distribution.