Modeling the effects of systematic variation in ionic strength on the attachment kinetics of Pseudomonas fluorescens UPER‐1 in saturated sand columns

We report the effects of salt type and concentration on the change in attachment kinetics when bacteria are pumped through a column of water‐saturated clean sand over relatively long periods of time (up to 35 pore volumes). The species Pseudomonas fluorescens UPER‐1 was found to exhibit three different kinds of attachment kinetics: first order, second order, and an intermediate order. The attachment kinetics of bacteria was modeled by using the advection‐dispersion equation coupled with a set of equations for each kind of attachment kinetics while using colloid filtration theory to predict collector efficiencies. At low or zero salt concentrations (≤10 −4 M ) a second‐order kinetics model (“blocking”), a “first‐order” kinetics model, and an intermediate‐order kinetics model (“ripening”), were all found to fit the data equally well. At intermediate and high salt concentrations (≥10 −3 M ) the ripening model was found to fit the data best. We report values for collision efficiencies of bacteria in the range 0.01–0.2, depending upon the salt type and concentration. This study points out the importance of long‐term experiments to study the effect of ionic strength on bacteria attachment kinetics in saturated porous media and the phenomenon of cell‐to‐cell attachment at high ionic strength. This study further points out the range of kinetics to expect when bacteria attach to natural porous media and suggests a modeling framework.