Transport of E. coli in columns of geochemically heterogeneous sediment.

To elucidate the parameters determining the transport of Escherichia coli in aquifers, the attachment of E. coli in low concentrations to column sediments was investigated. The sediments comprised 0.18-0.50mm quartz sand, grains coated with goethite, calcite grains or grains of activated carbon (AC), in varying fractions (lambda=0, 0.05, 0.1, 0.2, 0.4, 0.7, 1.0) and all of similar diameter to the quartz sand. The weighted sum of favourable and unfavourable sticking efficiencies (alpha(total)) showed that upon increasing the fraction of favourable mineral grains (lambda) there was an initial rapid increase, which then slowed down. This was most pronounced in the AC experiments, followed by the calcite experiments and then the goethite experiments. We ascribe this non-linear relation to surface charge and hydrophobic heterogeneity of the E. coli population.