Transport Of Bacteria In Porous Media Research Articles

Effects of graphene oxides on transport and deposition behaviors of bacteria in saturated porous media

The effects of graphene oxides on the transport and deposition behaviors of bacteria (Gram-negative Escherichia coli and Grampositive Bacillus subtilis) in quartz sand were investigated in both NaCl and CaCl2 solutions at pH 6.5. Both breakthrough curves and retained profiles of bacteria in the absence and presence of GO under all examined solution conditions were obtained. The results demonstrated that for both types of bacteria, the presence of GO increased the transport and decreased the deposition of bacteria at both low (10 mM) and high ionic strengths (50 mM) in NaCl solutions. However, opposite observations were achieved at different ionic strengths in CaCl2 solutions. Particularly, GO facilitated the transport and inhibited the deposition of bacteria in 1 mM CaCl2 solutions, while they suppressed the transport of bacteria in 2.5 mM CaCl2 solutions. Clearly, the cell transport and deposition behaviors in porous media would be greatly influenced by the GO copresent in suspensions. Furthermore, we found that with GO copresent in suspensions, the transport and deposition behaviors of bacteria were highly associated with those of GO. The heteroaggregation of bacteria and GO also contributed to the decreased cell transport in 2.5 mM CaCl2 solutions. This study showed that GO copresent in suspensions could act as mobile carriers for bacteria transport in porous media, leading to the alteration of cell transport and deposition behaviors.

Bayesian process-identification in bacteria transport in porous media

A Bayesian parameter estimation approach is developed for the estimation of joint probability distribution functions for colloid and bacterial fate and transport model parameters describing breakthrough curves (BTCs) obtained through porous media column studies, and is applied to data involving different ionic strength solutions to fit models of differing complexity. Our approach focuses on the simultaneous fitting of a number of BTCs representing different conditions, and it provides a measure of the goodness of model structure, namely Deviance Information Criteria (DIC). Comparison of DIC per model fit enables the evaluation of the significance of various processes through step-wise increases in complexity due to the addition of process model components. We use the method to investigate the transport of both flagellated and non-flagellated strains of Azotobacter vinelandii in a simulated porous media under three ionic strengths. Three different model structures are considered: one without a detachment process and with Langmuirian blocking function, one with detachment, and one with detachment and a second-order blocking function based on random sequential adsorption. First, the model was applied separately to each single BTC. Next, the model was applied comprehensively to the experiments under various ionic strengths, whereas some transport parameters including dispersivity, detachment coefficient, the fraction of cells undergoing irreversible attachment, and the coefficient of the second-order blocking term were assumed to be the same under different ionic strengths. In most cases, including detachment substantially improved the DIC as expected, whereas using the second-order blocking improved DIC for most of the cases when the method was applied to separate BTCs but not when the method was applied collectively to the three BTCs obtained under various ionic strengths. Also, comparing the outcomes of the separate applications of the parameter estimation algorithm versus the collective application indicates that the uncertainty associated with the estimated parameters is substantially smaller when the collective approach is used and also that the estimated parameters are more consistent with the expectations based on the underlying physical processes.

Influence of nutrient conditions on the transport of bacteria in saturated porous media

The influence of nutrient conditions on the transport of bacteria in packed porous media was examined in both NaCl and CaCl2–NaCl mixed solutions at pH 6.0. Two representative cell types, Bacillus subtilis (Gram-positive) and Escherichia coli DH5α (Gram-negative), were used to determine the influence of nutrient conditions on cell transport behavior. Under all examined solution conditions, the breakthrough plateaus in the presence of background nutrients in solutions for both examined bacteria types were higher than those without nutrients, indicating that the presence of nutrients in solution enhanced the bacteria transport regardless of the examined cell type (Gram-positive or Gram-negative) and solution chemistry (ionic strength and ion valence). The increased bacteria transport induced by the presence of nutrient in solutions was probably not driven by the changes in the sizes of bacteria, cell surface properties (i.e., zeta potentials), or the contents of extracellular polymeric substances (EPS) since these properties were not obviously changed by the presence of nutrients in solutions. Nutrient pre-equilibration experiments demonstrated that the deposition site competition by nutrients contributed to the increased bacteria transport observed with the presence of nutrients in bacterial suspension. Additional nutrient effects on cell transport were examined from the column experiments conducted in the absence of nutrients for the cells under 2-day starvation. Starvation of bacteria also increased the bacteria transport in porous media. The sizes of bacteria, zeta potentials of bacteria, and the EPS composition were changed by the starvation process, which might be responsible for the increased transport of starved bacteria observed for both cell types examined under all solution conditions.

Cotransport of Pseudomonas putida and kaolinite particles through water‐saturated columns packed with glass beads

This study is focused on Pseudomonas putida bacteria transport in porous media in the presence of suspended kaolinite clay particles. Experiments were performed with bacteria and kaolinite particles separately to determine their individual transport characteristics in water‐saturated columns packed with glass beads. The results indicated that the mass recovery of bacteria and clay particles decreased as the pore water velocity decreased. Batch experiments were carried out to investigate the attachment of Pseudomonas putida onto kaolinite particles. The attachment process was adequately described by a Langmuir isotherm. Finally, bacteria and kaolinite particles were injected simultaneously into a packed column in order to investigate their cotransport behavior. The experimental data suggested that the presence of clay particles significantly inhibited the transport of bacteria in water‐saturated porous media. The observed reduction of Pseudomonas putida recovery in the column outflow was attributed to bacteria attachment onto kaolinite particles, which were retained onto the solid matrix of the column. A mathematical model was developed to describe the transport of bacteria in the presence of suspended clay particles in one‐dimensional water‐saturated porous media. Model simulations were in good agreement with the experimental results.

Transport and fate of bacteria in porous media: Coupled effects of chemical conditions and pore space geometry

Experimental and theoretical studies were undertaken to explore the coupled effects of chemical conditions and pore space geometry on bacteria transport in porous media. The retention of Escherichia coli D21g was investigated in a series of batch and column experiments with solutions of different ionic strength (IS) and ultrapure quartz sand. Derjaguin–Landau–Verwey–Overbeek (DLVO) calculations and results from batch experiments suggested that bacteria attachment to the sand surface was negligible when the IS was less than or equal to 50 mM. Breakthrough data from column experiments showed significant cell retention and was strongly dependent on the IS. This finding indicates that cell retention was dependent on the depth of the secondary energy minimum which increases with IS. When the IS of the influent bacteria‐free solution was decreased to 1 mM, only a small fraction of the retained bacteria was released from the column. The remaining retained bacteria, however, were recovered from the sand, which was excavated from the column and suspended in a cell‐free electrolyte having the original IS. These observations suggest that the solution chemistry is not the only parameter controlling bacteria retention in the porous media. Computational simulations of flow around several collector grains revealed the retention mechanism, which is dependent on both the solution chemistry and the pore space geometry. Simulations demonstrate that the pore space geometry creates hydrodynamically disconnected regions. The number of bacterial cells that may be transported to these relatively “immobile” regions will theoretically be dependent on the depth of the secondary energy minimum (i.e., the IS). Once bacteria are trapped in these immobile regions, reduction of the secondary energy minimum does not necessarily release the cells owing to hydrodynamic constraints.

An improved spectrophotometric method to study the transport, attachment, and breakthrough of bacteria through porous media.

This study reports an improved spectrophotometric method for studying bacterial (Pseudomonas fluorescens UPER-1) transport and attachment in saturated porous media (silica sand). While studying the effect of ionic strength by the traditional packed-column spectrophotometric method, we encountered an artifact. The absorbance of a well-stirred bacterial suspension was found to decrease with time in the presence of high concentrations of sodium and potassium phosphate salts (> or = 10(-2) M) as the cells continued to age in a resting stage. Our results show that collision efficiency and a bed ripening index will be in error by as much as 20% if breakthrough is measured by the traditional spectrophotometric technique. We present an improved experimental technique that will minimize the artifact and should substantially advance the understanding of bacteria transport in porous media.