Effect of bacterial extracellular polymers on the saturated hydraulic conductivity of sand columns.

Columns were packed with clean quartz sand, sterilized, and inoculated with different strains of bacteria, which multiplied within the sand at the expense of a continuous supply of fresh nutrient medium. The saturated hydraulic conductivity (HCsat) of the sand was monitored over time. Among the four bacterial strains tested, one formed a capsule, one produced slime layers, and two did not produce any detectable exopolymers. The last two strains were nonmucoid variants of the first two. Only one strain, the slime producer, had a large impact on the HCsat. The production of exopolymers had no effect on either cell multiplication within or movement through the sand columns. Therefore, the HCsat reduction observed with the slime producer was tentatively attributed to the obstruction of flow channels with slime. Compared with the results with Arthrobacter sp. strain AK19 used in a previous study, there was a 100-fold increase in detachment from the solid substratum and movement through the sand of the strains used in this study. All strains induced severe clogging when they colonized the inlet chamber of the columns. Under these conditions, the inlet end was covered by a confluent mat with an extremely low HCsat.