Effects of Velocity on the Transport of Two Bacteria Through Saturated Sand

Transport of the bacteria Klebsiella oxytoca and Burkholderia cepacia G4PR1 (G4PR1) was investigated in column experiments conducted under conditions that allowed us to quantify sorption under a range of ground water velocities. Column experiments (33 mm I.D. × 114 mm long columns) were conducted at four linear water velocities (0.5 to 14 cm.hr −1 ) through a medium to coarse grained silica sand. The peak C/Co concentrations for both bacteria were attenuated with respect to a conservative tracer (Cl − ), and well‐defined tailing was observed. Breakthroughs of both bacteria were influenced by the water velocity. In the case of G4PR1, the attenuation of the peak C/Co concentrations increased as the velocity decreased while the peak C/Co concentrations for K. oxytoca were similar at velocities between 3 and 13 cmhr −1 but decreased at the lowest velocity tested (0.6 cm‐hr −1 ). The tailing reached constant C/Co values of between 2 × 10 −3 and 5 × 10 −3 , and between 2 × 10 −5 and 5 × 10 −5 for K. oxytoca and G4PR1 after 2t 0 . A one‐dimensional mathematical model for advective‐dispersive transport that accounts for irreversible (k irr ) and reversible (k f and k r ) sorption was used to quantify the sorption process. Both irreversible and reversible sorption was required to obtain good fits to the measured K. oxytoca data. Results of this modeling suggested that k irr and k r are independent of velocity and an empirical relationship was developed relating kf to velocity. For G4PR1, the best fits were obtained using only reversible sorption. Results of the modeling suggested that k f was independent of velocity at all velocities tested and k r was independent of velocity at velocities between 3 and 13 cmhr −1 . At the lowest velocity investigated (0.5 cmhr −1 ), the k f value decreased considerably. This study showed that sorption characteristics are bacteria specific, and are likely related to surface chemistry because G4PR1 is more hydrophobic than K. oxytoca . The study also showed that in order for bacterial transport experiments to be directly applicable to the subsurface, they should be conducted at velocities similar to those observed in the subsurface, or the relationship between the sorption parameter(s) and velocity should be known.