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 velociti es. Column experiments (33 mm I.D. x 114 mm long columns) were conducted at four linear water velocities (0.5 to 14 cm hr(-1)) through a medium to coa rse grained silica sand. The peak C/Co concentrations for both bacteria wer e 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 con centrations increased as the velocity decreased while the peak C/Co concent rations for K, oxytoca were similar at velocities between 3 and 13 cm hr(-1 ) but decreased at the lowest velocity tested (0.6 cm hr(-1)). The tailing reached constant C/Co values of between 2 X 10(-3) and 5 X 10(-3), and betw een 2 x 10(-5) and 5 x 10(-5) for K, oxytoca and G4PR1 after 2t(o). A one-d imensional mathematical model for advective-dispersive transport that accou nts for irreversible (k(irr)) and reversible (k(f) and k(f)) sorption was u sed to quantify the sorption process. Both irreversible and reversible sorp tion was required to obtain good fits to the measured K. oxytoca data. Resu lts of this modeling suggested that k(irr) and k(r) are independent of velo city and an empirical relationship was developed relating k(f) to velocity. For G4PR1, the best fits were obtained using only reversible sorption, Res ults of the modeling suggested that k(f) was independent of velocity at all velocities tested and k(r) was independent of velocity at velocities betwe en 3 and 13 cm hr(-1). At the lowest velocity investigated (0.5 cm hr(-1)), the kf value decreased considerably. This study showed that sorption chara cteristics are bacteria specific, and are likely related to surface chemist ry 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 param eter(s) and velocity should be known.