Effects of temperature and motility on the advective transport of a deep subsurface bacteria through saturated sediment.

摘要

Replicate column experiments were done to quantify the effects of temperature and bacterial motility on advective transport through repacked, but otherwise unaltered, natural aquifer sediment. The bacteria used in this study, A0500, was a flagellated, spore-forming rod isolated from the deep subsurface at DOE's Savannah River Laboratory. Motility was controlled by turning on flagellar metabolism at 18(degrees)C but off at 40(degrees)C. Microspheres were used to independently quantify the effects of temperature on the sticking efficiency ((alpha)), estimated using a steady-state filtration model. The observed greater microsphere removal at the higher temperature agreed with the physical-chemical model, but bacteria removal at 18(degrees)C was only half that at 4(degrees)C. The sticking efficiency for non-motile A0500 (4(degrees)C) was over three times that of the motile A0500 (18(degrees)C), 0.073 versus 0.022 respectively. Analysis of complete breakthrough curves using a non-steady, kinetically limited, transport model to estimate the time scales of attachment and detachment suggested that motile A 0500 bacteria traveled twice as far as non-motile A 0500 bacteria before becoming attached. Once attached, non-motile colloids detached on the time scale of 9 to 17 days. The time scale for detachment of motile A0500 bacteria was shorter, 4 to 5 days. Results indicate that bacterial attachment was reversible and detachment was enhanced by bacterial motifity. The kinetic energy of bacterial motility changed the attachment-detachment kinetics in favor of the detached state. The chemical factors responsible for the enhanced transport are not known. However, motility may have caused weakly held bacteria to detach from the secondary minimum, and possibly from the primary minimum, as described by DLVO theory.