Influence of nutrient conditions on the transport of bacteria in saturated porous media.

The influence of nutrient conditions on the transport of bacteria in packed porous media was examined in both NaCl and CaCl(2)-NaCl mixed solutions at pH 6.0. Two representative cell types, Bacillus subtilis (Gram-positive) and Escherichia coli DH5α (Gram-negative), were used to determine the influence of nutrient conditions on cell transport behavior. Under all examined solution conditions, the breakthrough plateaus in the presence of background nutrients in solutions for both examined bacteria types were higher than those without nutrients, indicating that the presence of nutrients in solution enhanced the bacteria transport regardless of the examined cell type (Gram-positive or Gram-negative) and solution chemistry (ionic strength and ion valence). The increased bacteria transport induced by the presence of nutrient in solutions was probably not driven by the changes in the sizes of bacteria, cell surface properties (i.e., zeta potentials), or the contents of extracellular polymeric substances (EPS) since these properties were not obviously changed by the presence of nutrients in solutions. Nutrient pre-equilibration experiments demonstrated that the deposition site competition by nutrients contributed to the increased bacteria transport observed with the presence of nutrients in bacterial suspension. Additional nutrient effects on cell transport were examined from the column experiments conducted in the absence of nutrients for the cells under 2-day starvation. Starvation of bacteria also increased the bacteria transport in porous media. The sizes of bacteria, zeta potentials of bacteria, and the EPS composition were changed by the starvation process, which might be responsible for the increased transport of starved bacteria observed for both cell types examined under all solution conditions.