Effects of transverse mixing on transport of bacteria through heterogeneous porous media (original) (raw)
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Colloids and Surfaces B-biointerfaces, 2006
The studies on transport of particles across porous systems are based on the Colloid Filtration Theory (CFT). According to CFT, the collision efficiency is constant along the system length [J.N. Ryan, M. Elimelech, Colloids Surf. A: Physicochem. Eng. Aspects 107 (1996) 1-56]. Decreasing values of collision efficiency have been reported, a phenomenon that has been interpreted as a deviation from the 841-852]. This paper presents data on transport of Bacillus megaterium spores through quartz sand columns. The occurrence of consecutive phases of increase and decrease of the values of C/C 0 , the effluent spore concentration expressed as a fraction of the influent spore concentration, is reported. These patterns of change in C/C 0 were interpreted as the result of the concomitant occurrence of blocking and ripening, the prevalence of these phenomena in different moments of the experiment, and the spatial distribution of the prevalence of blocking and ripening effects along the porous system. It is argued that this spatial distribution in the predominance of blocking and ripening, what leads to the intensification of ripening at the entrance of the porous system, might be a possible explanation for the reported deviation from the CFT for experimental conditions where ripening and blocking take place.
Physical and chemical factors influencing transport of microorganisms through porous media
Applied and Environmental Microbiology, 1991
Resting-cell suspensions of bacteria isolated from groundwater were added as a pulse to the tops of columns of clean quartz sand. An artificial groundwater solution (AGW) was pumped through the columns, and bacterial breakthrough curves were established and compared to test the effects of ionic strength of the AGW, cell size (by using strains of similar cell surface hydrophobicity but different size), mineral grain size, and presence of heterogeneities within the porous media on transport of the bacteria. The proportion of cells recovered in the effluent ranged from nearly 90% for AGW of a higher ionic strength (I = 0.0089 versus 0.00089 m), small cells (0.75-micron-diameter spheres versus 0.75 by 1.8-micron rods), and coarse-grained sand (1.0 versus 0.33 mm) to less than 1% for AGW of lower ionic strength, large cells, and fine-grained sand. Differences in the widths of peaks (an indicator of dispersion) were significant only for the cell size treatment. For treatments containing h...
Transport of bacteria in an aquifer sand: Experiments and model simulations
Water Resources Research, 1994
Experiments were carried out to determine the breakthrough of bacteria through a saturated aquifer sand at three flow velocities and three cell concentrations. Bacteria were either suspended in deionized water or 0.01 mol L -• NaCI solution. Bacterial transport was found to increase with flow velocity and cell concentration but was significantly retarded in the presence of 0.01 mol L -• NaC1. A mathematical model based on the advection-dispersion equation was formulated to describe bacterial transport and retention in porous media. The transport equations for bacteria were solved using the finite difference Crank-Nicolson scheme combined with Newton-Raphson iterations. The best fit of the numerical model to the experimental data was obtained using the downhill simplex optimization technique to minimize the sum of the squares of deviations between model predictions and experimental data by varying three parameters. This numerical model was found to describe the experimental data very well under all the experimental conditions tested. An alternative model (also based on the advection-dispersion equation) was tested against all the experimental data sets, but it did not represent the experimental data as well as the model proposed in this paper. face materials [e.g., Bitton et al., 1974; Wollum and Cassel, 1978; Smith et al., 1985; Parke et al., !986; Tan et al., 1991]. Many environmental factors such as ionic strength and flow velocity of the soil solution and properties of the porous materials have been identified to affect microbial transport in porous media in qualitative terms [e.g., Goldshrnid et al., 1973; Bitton et al., !974; Smith et al., !978; Wollum and Cassel, 1978; Gerba and Bitton, !984; McDowell-Boyer et al., 1986; Fontes et al., 1991; Gannon et al., 1991b; Gammack et al., 1992]. Complex mathematical models have also been developed to describe bacterial transport in porous media [e.g., Corapcioglu and Haridas, 1984, !985; Taylor and Jaffe, 1990]. Despite the experimental and modeling 1Now at Centre for Environmental Mechanics, CSIRO, Canben'a, Australia.
Transport of Viruses Through Saturated and Unsaturated Columns Packed with Sand
Transport in Porous Media, 2009
This study is focused on the transport of Pseudomonas (P.) putida bacterial cells in a 3-D model aquifer. The pilot-scale aquifer consisted of a rectangular glass tank with internal dimensions: 120 cm length, 48 cm width, and 50 cm height, carefully packed with well-characterized quartz sand. The P. putida decay was adequately represented by a firstorder model. Transport experiments with a conservative tracer and P. putida were conducted to characterize the aquifer and to investigate the bacterial behavior during transport in water saturated porous media. A 3-D, finite-difference numerical model for bacterial transport in saturated, homogeneous porous media was developed and was used to successfully fit the experimental data. Furthermore, theoretical interaction energy calculations suggested that the extended-DLVO theory seems to predict bacteria attachment onto the aquifer sand better than the classical DLVO theory.
International Journal of Water Resources Development
Understanding of bacteria transport within saturated porous media is essential for protecting groundwater from microbial contamination. In this research, the transport of E. coli in homogenous saturated porous media was investigated. The main objective was to evaluate velocity and behavior of E. coli transpor through Loamy sand layer. Comparing E. coli biological tracer with Uranine tracer and also hydraulic dispersion investigation are other purposes of this paper. To achieve these purposes, a physical model withthree sizes of particle were used in these transport experiments. The bacteria suspension were injected in a hole at one side and water were sampled in two holes located at axial distances of 20 and 60 cm from the injection point, two marginal sampling holes at a distance of 40 cm from the injection point and at the output of the model. The results indicated that the advection component has a significant influence on Bacteria movement, but in marginal holes the potency of a...
Straining phenomena in bacteria transport through natural porous media
Environmental Science and Pollution Research, 2010
Background, aim, and scope Transport of bacteria through natural porous media is an issue of increasing concern arising in several very important environmental processes. These include the percolation of bacteria from fecal waste to drinking water reservoirs, thus leading to a risk for human health, or the bioremediation of contaminated soils in which the bacteria are expected to travel long distances underground in order to reach contaminated areas and degrade chemicals originating from accidental spills. An understanding of bacterial retention and transport mechanisms in porous media would be of great help in the development of models able to predict the distance covered by bacterial suspensions in these situations. Materials and methods Experiments were carried out preparing columns filled of soil and sand, introducing bacteria culture (Escherichia coli, Pseudomona putida, and Listeria innocua) solutions by the top of the column. Breakthrough curves were obtained to see the transport of the bacteria in the column. Results The transport of different bacteria in the two soils aimed at establishing the relative importance of straining in different conditions. This has enabled us to obtain certain parameters, such as the sticking coefficients derived from the filtration theory or bacterial recoveries after multi-step elution, which aid our understanding of how bacteria are retained by mechanisms different to those usually included in the physico-chemical filtration theory. Discussion Several indicators may be used to determine the degree of relevance of straining as a mechanism acting during bacterial transport through porous media. Usually, in natural media, neither straining nor physicochemical filtration is the sole mechanism contributing to bacterial retention. The retention of bacteria by straining mechanisms can be assessed by means of elution profiles under varying conditions. The inversion of flow in our experiments gave rise to secondary elution peaks, probably originating from bacteria retained in narrow pores Conclusions According to experimental observations, straining was shown to contribute highly to bacterial retention in all the soils tested, in particular in the soils with a broader grain size distribution and more irregular shape. In both media, an increase in ionic strength did not lead to significant differences in bacterial retention, possibly due to the lack of relevance of ionic repulsion as a barrier to physico-chemical attachment of particles Recommendation and perspectives The study of bacteria transport in natural soil is an important step in the development of decontamination processes. The importance of the straining in the transport process has been revealed in the work carried out in this paper. Keywords Bacterial straining. Escherichia coli. Filtration. Listeria innocua. Pseudomona putida. Soil column 1 Background, aim, and scope Bacterial transport in the subsurface is a subject of increasing interest due to its application in fields such as soil bioremediation (Fontes et al., 1991) or aquifer contamination by pathogenic microorganisms (Foppen 2002).
Effects of porous media preparation on bacteria transport through laboratory columns
Water Research, 2002
Bacterial and colloid transport experiments related to environmental systems are typically performed in the laboratory, with sand often used as the porous media. In order to prepare the sand, mechanical sieving is frequently used to tighten the sand grain size distribution. However, mechanical sieving has been reported to provide insufficient repeatability between identical colloidal transport experiments. This work examined the deficiencies of mechanical sieving with respect to bacterial transport through sand columns. It was found that sieving with standard brass sieves (1) contaminates the sand with copper and zinc as a linear function of sieving time and (2) inefficiently sizes sand grains below 300 mm (the largest size examined in this study) due to rapid clogging of the sieves. A procedure was developed that allows utilization of brass sieves for sizing the sand grains and removes the metal contamination introduced from the sieves. Bacterial transport experiments utilizing this column preparation procedure gave repeatable breakthrough curves. Further examination of the effects of these treatments on bacterial transport showed interesting results. First, it was found that the metal contamination did not affect the clean-bed bacterial transport. Second, it was found that variations of the column flushing procedure did not alter the clean-bed breakthrough of the bacteria, but did alter the inter-particle blocking. Finally, it was found that the shape of the sand grains (oblong vs. rounded) significantly alters the bacterial transport, with the transport being dominated by the smallest dimension of the oblong grains.
Journal of Contaminant Hydrology, 2011
The main objective of this study was to evaluate the combined effects of grain size and pore water velocity on the transport in water saturated porous media of three waterborne fecal indicator organisms (Escherichia coli, MS2, and ΦX174) in laboratory-scale columns packed with clean quartz sand. Three different grain sizes and three pore water velocities were examined and the attachment behavior of Escherichia coli, MS2, and ΦX174 onto quartz sand was evaluated. The mass recoveries of the biocolloids examined were shown to be highest for Escherichia coli and lowest for MS2. However, no obvious relationships between mass recoveries and water velocity or grain size could be established from the experimental results. The observed mean dispersivity values for each sand grain size were smaller for bacteria than coliphages, but higher for MS2 than ΦX174. The single collector removal and collision efficiencies were quantified using the classical colloid filtration theory. Furthermore, theoretical collision efficiencies were estimated only for E. coli by the Interaction-Force-Boundary-Layer, and Maxwell approximations. Better agreement between the experimental and Maxwell theoretical collision efficiencies were observed.