Abstract
The development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing; however, we are lacking experimental data and models to predict bacterial movement through rock matrices. Here, breakthrough curves (BTCs) were obtained to quantify the transport of the ureolytic bacterium, Sporosarcina pasteurii, through sandstone cores, as a function of core length (1.8–7.5cm), bacterial density (4×106 to 9×107cells/ml) and flow rate (5.8–17.5m/s). S. pasteurii was easily immobilised within the homogeneous sandstone matrix (>80%) in comparison to a packed sand column (<20%; under similar experimental conditions), and percentage recovery decreased almost linearly with increasing rock core length. Moreover, a decrease in bacterial density or flow rate enhanced bacterial retention. A numerical model based on 1D advection dispersion models used for unconsolidated sand was fitted to the BTC data obtained here for sandstone. Good agreement between data and model was obtained at shorter rock core lengths (<4cm), suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths. Discrepancies were, however observed at longer core lengths and with varying flow rates, indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length. Implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed.
Highlights
Accurate prediction of bacterial transport is valuable for risk assessment of pathogenic organisms introduced to the subsurface environment by infiltrating wastewaters (e.g., Pachepsky et al, 2006)
Initial modelling of the tracer experiments provided an estimate of the hydrodynamic dispersivity, a = 0.75 cm, and this value was used for modelling of bacterial breakthrough curves (BTCs) (Table 2)
Bacterial breakthrough curves exhibited considerably lower recovery values compared to the tracer experiments, ranging from 10% to 75% (Table 1)
Summary
The transport of microorganisms through porous rock media is a crucial factor for a variety of subsurface remediation and engineering technologies including in situ bioremediation of contaminants (e.g., Li et al, 2011), microbially enhanced oil recovery (Shabani et al, 2011) and microbially induced mineral precipitation for pore space and fracture plugging to control fluid flow (e.g., Cuthbert et al, 2013; Ferris et al, 1996; Phillips et al, 2013; Tobler et al, 2012), soil stabilization (e.g., van Paassen et al, 2010 and reference therein) and solid-phase capture of pollutants (e.g., Fujita et al, 2010; Lauchnor et al, 2013; Mitchell and Ferris, 2005). Transport of bacteria can vary considerably between different bacterial strains even when they exhibit similar cell morphologies and surface characteristics (Liu et al, 2011; Stumpp et al, 2011). This suggests that transport parameters cannot be generalised and need to be determined for each organism individually. A disadvantage of packed column experiments is that they lack the porosity, permeability, hydrodynamics and heterogeneities of consolidated rock systems: factors that have a marked impact on transport in the subsurface
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