Transport and attenuation of bacteria and bacteriophages in an alluvial gravel aquifer

Abstract

The relative attenuation of rhodamine WT dye, two strains of Escherichia coli, Bacillus subtilis endospores, and the F-RNA bacteriophage MS2 in an alluvial gravel aquifer was investigated in two tracing experiments at Burnham, near Christchurch, New Zealand. A simulated concentration curve was fitted to the observed breakthrough curves using the contaminant transport model AT123D, by optimising hydraulic conductivity (K), longitudinal dispersivity (α x ), and a removal constant (λ) (which includes die-off and physical removal processes) with the Parameter Estimation (PEST) optimisation routine. When comparing the parameters, the hydraulic conductivity was converted to velocity (V). The V ranking was E. coli 2690 > B. subtilis endospores > rhodamine WT in Experiment 1 and E. coli J6-2 > phage MS2 > rhodamine WT in Experiment 2. These rankings are consistent with the concept of pore size exclusion, whereby larger particles are preferentially transported in the larger interconnected pores where water velocities are higher. The longitudinal dispersivity (α x ) rankings were consistent with pore size exclusion in Experiment 1, and broadly consistent in Experiment 2. Of the two parameters, V is considered to provide the more reliable result, because it is easier to determine peak position in time than peak height. Little useful information could be derived from the λ values in our study, because of high levels of uncertainty associated with determining peak heights, particularly in Experiment 1. Overall, the curve fits were better in Experiment 2, because of a greater number of bores and observations. Although this complicated between-experiment comparisons, an overall retardation (R) ranking of rhodamine WT > phage MS2; B. subtilis endospores > E. coli J6-2 > E. coli 2690 is broadly consistent with pore size exclusion. Overall, our study showed that the application of the AT123D model to the observed velocities of the tracer curves demonstrated an effect consistent with pore size exclusion.

Processes in Microbial Transport in the Natural Subsurface

“…This approach was demonstrated to be effective at simulating observed large exclusion effects (bacterial velocities nearly double that of conservative tracers) with minimal truncation (on the order of 5%) of the dispersive displacement distribution. This approach also leads to decreased apparent dispersion of the bacteria relative to conservative tracers, consistent with theoretical considerations and observations [116].…”

“…They observed faster velocities of the bacteria relative to inert tracers, and estimated total removal rates of 2.4-9.4 day À1 . Sinton et al [116] further examined the apparent velocities of microbial (bacteria and virus) and inert tracers, and found that apparent velocity increased, and apparent dispersion decreased, with increasing particle size.…”

“…Termed pore exclusion [127], this has been suggested as a velocity enhancement of the excluded material in natural aquifers (Gvirtzman and Gorelick [48], for anions in unsaturated flow; Rehmann et al [97] for virus transport). Note that pore exclusion is also termed specifically ''size exclusion'' by some authors [98], as well as various other terms such as ''volume exclusion'' [4], ''pore size exclusion'' [116], or ''size exclusion chromatography'' [50]. The term ''differential advection'' has also been introduced [138,139] to generally describe the phenomenon of earlier breakthrough of colloids relative to a solute tracer without specific regard to the mechanism.…”

Transport of multiple Escherichia coli strains in saturated porous media

“…This type of sorption was absent in the E. coli strains obtained from the Rotterdam Zoo in the work of Foppen et al (2010). In addition, Foppen and Schijven (2006) reported that, based on a number of studies, equilibrium sorption in E. coli transport was of little significance (Pang et al, 2003;Powelson and Mills, 2001;Sinton et al, 1997;Sinton et al, 2000;Alexander and Seiler, 1983;Havemeister and Riemer, 1985, both in: Matthess et al, 1985and in Matthess et al, 1988Champ and Schroeter, 1988;Merkli, 1975). Although the role equilibrium sorption plays in most of the strains we used in this work was indeed also rather limited, the role of kinetic attachment was at least equally limited.…”

Factors that Influence the Transport of Bacillus cereus Spores through Sand

“…In contrast to the large number of studies investigating virus and bacterial transport, very few studies were conducted using bacterial spores. Sinton et al (2000) used pore size exclusion to explain the transport retardation of rhodamine WT dye, followed by MS2, Bacillus subtilis spores, E. coli J6-2, and E. coli 2690. Schijven et al (2003) found that MS2 and Clostridium bifermentans spores can travel greater distances than Escherichia coli (E. coli).…”