Interactions between laponite and microbial biofilms in porous media: implications for colloid transport and biofilm stability

Quartz sand columns and sand-filled microscope flow cells were used to investigate the transport characteristics of the clay colloid laponite, and a biofilm-forming bacterium, Pseudomonas aeruginosa SG81. Separate experiments were performed with each particle to determine their individual transport characteristics in clean sand columns. In a second set of experiments, bacterial biofilms were formed prior to introduction of the clay colloids. In the independent transport experiments, bacteria and laponite each conformed to known physicochemical principles. A sodium chloride concentration of 7 x 10(-2) M caused complete retention of the laponite within the sand columns. P. aeruginosa SG81 was generally less influenced by ionic strength effects; it showed relatively low mobility at all ionic strengths tested and some (albeit reduced) mobility when introduced to the columns in 1M NaCl, the highest concentration tested, but nevertheless showed reproducible trends. Under conditions favourable to laponite retention and biofilm stability (7 x 10(-2) MNaCl), laponite suspensions were able to remobilise a portion of the attached bacterial biomass. At low ionic strength, the profile of laponite elution was also altered in the presence of a P. aeruginosa biofilm. These observations suggest that while a reduction in ionic strength has a dominant influence on the mobilisation of biological and inorganic colloids, the presence of laponite and biomass can have a distinct influence on the mobility of both types of colloids. Since these events are likely to occur in subsurface environments, our results suggest that colloid-biofilm interactions will have implications for colloid-bound contaminant transport and the remobilisation of pathogens.     

Colloid transport in porous media: impact of hyper-saline solutions

The transport of colloids suspended in natural saline solutions with a wide range of ionic strengths, up to that of Dead Sea brines (10^0.9 M) was explored. Migration of microspheres through saturated sand columns of different sizes was studied in laboratory experiments and simulated with mathematical models.Colloid transport was found to be related to the solution salinity as expected. The relative concentration of colloids at the columns outlet decreased (after 2-3 pore volumes) as the solution ionic strength increased until a critical value was reached (ionic strength > 10^−1.8 M) and then remained constant above this level of salinity.The colloids were found to be mobile even in the extremely saline brines of the Dead Sea. At such high ionic strength no energetic barrier to colloid attachment was presumed to exist and colloid deposition was expected to be a favorable process. However, even at these salinity levels, colloid attachment was not complete and the transport of ∼30% of the colloids through the 30-cm long columns was detected.To further explore the deposition of colloids on sand surfaces in Dead Sea brines, transport was studied using 7-cm long columns through which hundreds of pore volumes were introduced. The resulting breakthrough curves exhibited a bimodal shape whereby the relative concentration (C/C₀) of colloids at the outlet rose to a value of 0.8, and it remained relatively constant (for the ∼18 pore volumes during which the colloid suspension was flushed through the column) and then the relative concentration increased to a value of one. The bimodal nature of the breakthrough suggests different rates of colloid attachment. Colloid transport processes were successfully modeled using the limited entrapment model, which assumes that the colloid attachment rate is dependent on the concentration of the attached colloids. Application of this model provided confirmation of the colloid aggregation and their accelerated attachment during transport through soil in high salinity solution.     

Coupling of physical and chemical mechanisms of colloid straining in saturated porous media

Filtration theory does not include the potential influence of pore structure on colloid removal by straining. Conversely, previous research on straining has not considered the possible influence of chemical interactions. Experimental and theoretical studies were therefore undertaken to explore the coupling of physical and chemical mechanisms of colloid straining under unfavorable attachment conditions (pH=10). Negatively charged latex microspheres (1.1 and 3mum) and quartz sands (360, 240, and 150mum) were used in packed column studies that encompassed a range in suspension ionic strengths (6-106mM) and Darcy water velocities (0.1-0.45cmmin(-1)). Derjaguin-Landau-Verwey-Overbeek (DLVO) calculations and torque analysis suggests that attachment of colloids to the solid-water interface was not a significant mechanism of deposition for the selected experimental conditions. Effluent concentration curves and hyperexponential deposition profiles were strongly dependent on the solution chemistry, the system hydrodynamics, and the colloid and collector grain size, with greater deposition occurring for increasing ionic strength, lower flow rates, and larger ratios of the colloid to the median grain diameter. Increasing the solution ionic strength is believed to increase the force and number of colloids in the secondary minimum of the DLVO interaction energy profile. These weakly associated colloids can be funneled to small regions of the pore space formed adjacent to grain-grain junctions. For select systems, the ionic strength of the eluant solution was decreased to 6mM following the recovery of the effluent concentration curve. In this case, only a small portion of the deposited colloids was recovered in the effluent and the majority was still retained in the sand. These observations suggest that the extent of colloid removal by straining is strongly coupled to solution chemistry.     

Influence of biofilm on the transport of fullerene (C60) nanoparticles in porous media

The significance of biofilm on fullerene C₆₀ nanoparticles transport and deposition were examined both in porous media and quartz crystal microbalance with dissipation (QCM-D) systems under a variety of environmentally relevant ionic strength (1-25 mM in NaCl and 0.1-5 mM in CaCl₂) and flow conditions (4-8 m day⁻¹). The magnitudes of deposition rate coefficients (k_d) were compared between porous media with and without biofilm extracellular polymeric substances (EPS) coating under equivalent fluid velocities and solution chemistries. The observed k_d were greater in porous media with biofilm EPS coating relative to those without biofilm EPS coating across the entire solution ionic strengths and fluid velocities examined, demonstrating that the enhancement of C₆₀ deposition by the biofilm EPS coating is relevant to a wide range of environmental conditions. This greater deposition was also observed on silica surfaces with biofilm EPS coating in QCM-D system. The results clearly showed that biofilm EPS have a great influence on C₆₀ deposition. Derjaguin-Landau-Verwey-Overbeek (DLVO) theory could not explain the enhanced C₆₀ deposition by biofilm EPS. Biochemical and physical characteristics of biofilm EPS were responsible for the increased C₆₀ deposition.     

Characteristics of two types of stabilized nano zero-valent iron and transport in porous media

Nano-scale zero-valent iron (NZVI) has been shown to be suitable for remediating contaminated aquifers. However, they usually aggregate rapidly and result in a very limited migration distance that inhibits their usefulness. This study employed poly acrylic acid (PAA) and carboxymethyl cellulose (CMC) to synthesize two types of stabilized styles of NZVI with finer sizes (namely PNZVI and CNZVI). The mobility of stabilized NZVI was also demonstrated on the basis of transport in porous media. The results show that the PNZVI has a uniform particle size of 12 nm. However, tens of CNZVI particles with diameters of 1-3 nm were packed into secondary particles. Both the PNZVI and the CNZVI exhibited amorphous structures, and the stabilizer was bound to particle surfaces in the form of bidentate bridging via the carboxylic group, which could provide both electrostatic and steric repulsion to prevent particle aggregation. This study also proposes presumed stabilized configurations of PNZVI and CNZVI to reasonably illustrate their different dispersed suspension types. On the basis of the breakthrough curves and mass recovery, this study observed that the mobility of PNZVI in classic Ca²⁺ concentration of groundwater was superior to CNZVI. Nonetheless, the mobility of CNZVI would be decreased less significantly than PNZVI when encountering high Ca²⁺ concentrations (40 mM). Presumably, increasing the pore flow velocity would enhance the mobility of stabilized NZVI. Overall, the results of this study indicate that PNZVI has the potential to become an effective reactive material for in situ groundwater remediation.     

Influence of tetracycline resistance on the transport of manure-derived Escherichia coli in saturated porous media

In this research, tetracycline resistant (tet^R) and tetracycline susceptible (tet^S) Escherichia coli isolates were retrieved from dairy manure and the influence of tetracycline resistance on the transport of E. coli in saturated porous media was investigated through laboratory column transport experiments. Experimental results showed that tet^RE. coli strains had higher mobility than the tet^S strains in saturated porous media. Measurements of cell surface properties suggested that tet^RE. coli strains exhibited lower zeta potentials than the tet^S strains. Because the surface of clean quartz sands is negatively charged, the repulsive electrostatic double layer (EDL) interaction between the tet^R cells and the surface of sands was stronger and thus facilitated the transport of the tet^R cells. Although no difference was observed in surface acidity, cell size, lipopolysaccharides (LPS) sugar content and cell-bound protein levels between the tet^R and tet^S strains, they displayed distinct outer membrane protein (OMP) profiles. It was likely that the difference in OMPs, some potentially related to drug efflux pumps, between the tet^R and tet^S strains led to alteration in cell surface properties which in turn affected cell transport in saturated porous media. Findings from this research suggested that manure-derived tet^RE. coli could spread more widely in the groundwater system and pose serious public health risks.     

Coupled factors influencing the transport and retention of Cryptosporidium parvum oocysts in saturated porous media

The coupled role of solution ionic strength (IS), hydrodynamic force, and pore structure on the transport and retention of viable Cryptosporidium parvum oocyst was investigated via batch, packed-bed column, and micromodel systems. The experiments were conducted over a wide range of IS (0.1-100 mM), at two Darcy velocities (0.2 and 0.5 cm/min), and in two sands (median diameters of 275 and 710 μm). Overall, the results suggested that oocyst retention was a complex process that was very sensitive to the solution IS, the Darcy velocity, and the grain size. Increasing IS led to enhanced retention of oocysts in the column, which is qualitatively consistent with predictions of Derjaguin-Landau-Verwey-Overbeek theory. Conversely, increasing velocity and grain size resulted in less retention of oocysts in the column due to the difference in the fluid drag force and the rates of mass transfer from the liquid to the solid phase and from high to low velocity regions. Oocyst retention was controlled by a combined role of low velocity regions, weak attractive interactions, and/or steric repulsion. The contribution of each mechanism highly depended on the solution IS. In particular, micromodel observations indicated that enhanced oocyst retention occurred in low velocity regions near grain-grain contacts under highly unfavorable conditions (IS = 0.1 mM). Oocyst retention was also found to be influenced by weak attractive interactions (induced by the secondary energy minimum, surface roughness, and/or nanoscale chemical heterogeneity) when the IS = 1 mM. Reversible retention of oocysts to the sand in batch and column studies under favorable attachment conditions (IS = 100 mM) was attributed to steric repulsion between the oocysts and the sand surface due to the presence of oocyst surface macromolecules. Comparison of experimental observations and theoretical predictions from classic filtration theory further supported the presence of this weak interaction due to steric repulsion.     

Influence of movements on contaminant transport in an operating room

The influence of persons' movements on contaminant transport during an orthopedic surgical operation is examined. Orthopedic surgical operations require an ultra clean environment usually provided by a LAF device (laminar airflow). During hip replacements bone cement is sometimes applied. Due to practical reasons cement mixing is performed outside the LAF area. During the cement transport from the mixing location to the surgeon there is a potential risk of bacterial transport to the clean zone. This phenomenon is examined by smoke visualization and computational fluid dynamics (CFD). The movements are modeled by CFD using distributed momentum sources as well as a turbulent kinetic energy source. A significant risk of contaminant transport from the less clean zone to the ultra clean zone is found. The results indicate that it is possible to simulate the influence of movements using a relatively simple CFD model that considers the significant influence of a transient phenomenon in an approximate way. PRACTICAL IMPLICATIONS: In real-life ventilated enclosures like operating rooms movements take place. Persons' movements may influence the local flow field as well as the contaminant field substantially. Most often movements are ignored in simulations due to the complexity of the phenomenon. This paper presents an indirect and simple method to consider the influence of movements that may enable modelers to include this important phenomenon in the engineering application of CFD. This may improve practical risk assessment--for instance risk assessment of unintended transport of bacteria during orthopedic surgical operations that may jeopardize the hygiene.     

Aggregation and transport of nano-TiO2 in saturated porous media: effects of pH, surfactants and flow velocity

Transport of manufactured nano-TiO₂ in saturated porous media was investigated as a function of morphology characteristics, pH of solutions, flow velocity, and the presence of anionic and non-ionic surfactants in different concentrations. Surfactants enhanced the transport of nano-TiO₂ in saturated porous media while a pH approaching the point of zero charge of nano-TiO₂ limited their transport. The deposition process, a retention mechanism of nano-TiO₂ in saturated porous media was impacted by surfactant and pH. In Dispersion 1 systems (pH 7), the size of the nano-TiO₂ aggregates was directly related to the presence of surfactants. The presence of non-ionic surfactant (Triton X-100) induced a size reduction of nano-TiO₂ aggregates that was dependent on the critical micelle concentration. In Dispersion 2 systems (pH 9), the stability provided by the pH had a significant effect on the size of nano-TiO₂ aggregates; the addition of surfactants did impact the size of the nano-TiO₂ aggregates but in less significance as compared to Dispersion 1 systems. The electrostatic and steric repulsion forces in connection with the size of nano-TiO₂ aggregates and flow velocity impacted the single-collector efficiency and attachment efficiency which dictated the maximum transport distance of nano-TiO₂ for the Dispersion 1 and Dispersion 2 systems. By doubling the flow velocity at pH 9, the No Surfactant, 50% CMC Triton X-100, 100% CMC Triton X-100 and 100% CMC SDBS dispersion systems allowed nano-TiO₂ to attain maximum transport distances of 0.898, 2.17, 2.29 and 1.12 m, respectively. Secondary energy minima played a critical role in the deposition mechanisms of nano-TiO₂. Nano-TiO₂ deposited in the secondary energy wells may be released because of changes in solution chemistry. The deposition of nano-TiO₂ in primary and secondary energy minima, the reversibility of their deposition should be characterized to analyze the transport of nanoparticles in porous media. This is necessary to assess the risk of nanoparticles to the environment and public health.     

重力对饱和多孔介质中颗粒输运特性的影响

利用室内土柱试验研究重力对饱和多孔介质中颗粒输运特性的影响,包括渗流方向自上向下和自下向上两种不同的试验系列,每个系列中进行了5种不同渗流速度的试验。研究结果表明,渗流方向自上向下时的流出液中颗粒的浓度峰值要大于自下向上时的浓度峰值,并且前者的浓度峰值出现的也快。同一渗流方向条件下,渗流速度越大,流出液中颗粒的浓度峰值越大。其次,渗流自上向下时,随着渗流速度的增加,弥散度的值随之减小,但在渗流自下向上时,渗流速度的变化对弥散度的影响很小。另外,同一渗流方向中,随渗流速度增大,沉积系数逐渐减小,回收率逐渐增大,并且沉积系数在渗流自下向上时较渗流自上向下时的要大。可见,重力和渗流速度是影响饱和多孔介质中颗粒输运的重要因素,渗流速度越小,重力的作用越明显。     

Direct observations of colloid retention in granular media in the presence of energy barriers, and implications for inferred mechanisms from indirect observations

In this paper we present direct observations of retention of colloids in granular porous media over a large size range (0.21-9.0 μm) and generalize the significance of attachment in grain to grain contacts and attachment on the open surface as a function of colloid:collector ratio. We examine reversibility of attachment via these mechanisms with respect to ionic strength reduction and fluid velocity increase. We relate these direct observations to existing literature, and in some cases offer alternative interpretations of mechanisms of retention drawn from indirect observations (e.g. via column effluent and retained concentrations).     

Influence of organic matter on the transport of Cryptosporidium parvum oocysts in a ferric oxyhydroxide-coated quartz sand saturated porous medium

To assess the effect of organic matter on the transport of Cryptosporidium parvum oocysts in a geochemically heterogeneous saturated porous medium, we measured the breakthrough and collision efficiencies of oocysts as a function of dissolved organic matter concentration in a flow-through column containing ferric oxyhydroxide-coated sand. We characterized the surface properties of the oocysts and ferric oxyhydroxide-coated sand using microelectrophoresis and streaming potential, respectively, and the amount of organic matter adsorbed on the ferric oxyhydroxide-coated sand as a function of the concentration of dissolved organic matter (a fulvic acid isolated from Florida Everglades water). The dissolved organic matter had no significant effect on the zeta potential of the oocysts. Low concentrations of dissolved organic matter were responsible for reversing the charge of the ferric oxyhydroxide-coated sand surface from positive to negative. The charge reversal and accumulation of negative charge on the ferric oxyhydroxide-coated sand led to increases in oocyst breakthrough and decreases in oocyst collision efficiency with increasing dissolved organic matter concentration. The increase in dissolved organic matter concentration from 0 to 20 mg L⁻¹ resulted in a two-fold decrease in the collision efficiency.     

Influence of water chemistry and travel distance on bacteriophage PRD-1 transport in a sandy aquifer

Experiments were conducted to evaluate the impact of groundwater chemistry and travel distance on the transport and fate behavior of PRD-1, a bacteriophage employed as a surrogate tracer for pathogenic enteric viruses. The experiments were conducted in the unconfined aquifer at the United States Geological Survey Cape Cod Toxic-Substances Hydrology Research Site in Falmouth, Massachusetts. The transport behavior of bromide (Br(-)) and PRD-1 were evaluated in a sewage-effluent contaminated zone and a shallower uncontaminated zone at this site. Several multilevel sampling devices located along a 13-m transect were used to collect vertically discrete samples to examine longitudinal and vertical variability of PRD-1 retardation and attenuation. The concentration of viable bacteriophage in the aqueous phase decreased greatly during the first few meters of transport. This decrease is attributed to a combination of colloid filtration (attachment) and inactivation. The removal was greater (10(-12) relative recovery) and occurred within the first meter for the uncontaminated zone, whereas it was lesser (10(-9) relative recovery) and occurred over 4m in the contaminated zone. The lesser removal observed for the contaminated zone is attributed to the influence of sorbed and dissolved organic matter, phosphate, and other anions, which are present in higher concentrations in the contaminated zone, on PRD-1 attachment. After the initial decrease, the aqueous PRD-1 concentrations remained essentially constant in both zones for the remainder of the tests (total travel distances of 13 m), irrespective of variations in geochemical properties within and between the two zones. The viable, mobile PRD-1 particles traveled at nearly the rate of bromide, which was used as a non-reactive tracer. The results of this study indicate that a small fraction of viable virus particles may persist in the aqueous phase and travel significant distances in the subsurface environment.     

Macromolecule mediated transport and retention of Escherichia coli O157:H7 in saturated porous media

The role of extracellular macromolecules on Escherichia coli O157:H7 transport and retention was investigated in saturated porous media. To compare the relative transport and retention of E. coli cells that are macromolecule rich and deficient, macromolecules were partially cleaved using a proteolytic enzyme. Characterization of bacterial cell surfaces, cell aggregation, and experiments in a packed sand column were conducted over a range of ionic strength (IS). The results showed that macromolecule-related interactions contribute to retention of E. coli O157:H7 and are strongly linked to solution IS. Under low IS conditions (IS ≤ 0.1 mM), partial removal of the macromolecules resulted in a more negative electrophoretic mobility of cells and created more unfavorable conditions for cell-quartz and cell-cell interactions as suggested by Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction energy profiles and cell aggregation kinetics. Consequently, less retention was observed for enzyme treated cells in the corresponding column experiments. In addition, a time-dependent deposition process (i.e., ripening) was observed for untreated cells, but not for treated cells, supporting the fact that the macromolecules enhanced cell-cell interactions. Additional column experiments for untreated cells under favorable conditions (IS ≥ 1 mM) showed that a significant amount of the cells were reversibly retained in the column, which contradicts predictions of DLVO theory. Furthermore, a non-monotonic cell retention profile was observed under favorable attachment conditions. These observations indicated that the presence of macromolecules hindered irreversible interactions between the cells and the quartz surface.     

Influence of solution ionic strength on the collision efficiency distribution and predicted transport distance of a Sphingomonas sp. flowing through porous media

The effects of solution ionic strength on the collision efficiency (alpha) distribution of a Sphingomonas sp. were investigated using multiple sand columns of varying lengths and analyzing the bacteria clean-bed breakthrough concentrations using a distributed colloid filtration theory (D-CFT). Five different probability density functions (PDFs) were investigated and all accurately replicated the lab-scale experimental data, whereas a single alpha value could not. The alpha distribution shifted toward smaller values with decreasing ionic strength and the PDF parameters were strongly correlated to the Debye length, indicating that electrostatic interactions had a direct impact on the alpha distribution. The results indicate that while ionic strength has a large impact on bacterial transport distances for a concentration reduction of a few orders of magnitude, as occurs at the laboratory scale, due to the distributed nature of the collision efficiency, it has a minor effect on predicted transport distances required to achieve concentration reductions on the order of 10(6), which occurs at the field scale. Because of this, bacterial inactivation (e.g., death), rather than physically removing the bacteria from solution via filtration, is likely the key process impacting the transport of viable bacteria at the field scale. Overall, for systems with a distributed alpha, the results indicate that ionic strength has a strong influence on the transport of bacteria at the lab-scale (centimeters to one meter), both ionic strength and bacterial inactivation are important at the meso-scale (tens of meters), and inactivation becomes the dominant mechanism for reducing the transport of viable bacteria at the field scale (hundreds of meters).     

Coupled simulation of heat and moisture transport in air and porous materials for the assessment of moisture related damage

This paper describes the coupling of a model for heat and moisture transport in porous materials to a commercial Computational Fluid Dynamics (CFD) package. The combination of CFD and the material model makes it possible to assess the risk of moisture related damage in valuable objects for cases with large temperature or humidity gradients in the air. To couple both models the choice was made to integrate the porous material model into the CFD package. This requires the heat and moisture transport equations in the air and the porous material to be written down in function of the same transported variables. Validation with benchmark experiments proved the good functionality of the coupled model. A simulation study of a microclimate vitrine for paintings shows that phenomena observed in these vitrines are well predicted by the model and that data generated by the model provides additional insights in the physical mechanisms behind these phenomena.     

Influence of human movement on the transport of airborne infectious particles in hospital

The impacts of human movement on the distribution of airborne infectious particles in hospital environment are investigated numerically. In the case of airborne infection isolation room, the influence of different walking speeds on the distribution of respiratory droplets is investigated by adopting the Lagrangian method for tracing the motion of droplets, the dynamic mesh model for describing human walking and the Eulerian unsteady Reynolds-averaged Navier–Stokes model for solving the airflow. In the case of operating theatre, the impact of surgeon bending movement on the distribution of bacteria-carrying particles (BCPs) is investigated by using a similar approach, except that the drift-flux model is used for modelling BCPs distribution. The adopted models are successfully validated against reported experimental data. The results show that both walking speed and bending posture change considerably the suspended droplets concentration in a room. The key factors regarding the simulation techniques are discussed.     

An explicit formulation of the macroscopic strength criterion for porous media with pressure and Lode angle dependent matrix under axisymmetric loading

This paper aims to propose an explicit formulation of the macroscopic strength criterion for porous media with spherical voids.The matrix is assumed rigid and perfectly plastic with yield surface described by the three-parameter strength criterion,which is Lode angle and pressure dependent and capable of accounting for distinct values of the uniaxial tensile strength,uniaxial compressive strength(UCS) and equal biaxial compressive strength(eBCS).An exact upper bound of the macroscopic strength is derived for porous media subjected to purely hydrostatic loading.Besides,an estimate of the macroscopic strength profile of porous media under axisymmetric loading is obtained in parametric form.Moreover,a heuristic strength criterion in explicit form is further developed by examining limit cases of the parametric strength criterion.The developed strength criteria are assessed by finite-element based numerical solutions.Compared with the parametric strength criterion which involves cumbersome functions,the heuristic one is convenient for practical applications.For specific values of the matrix's strength surface,the proposed heuristic strength criterion can recover the well-known Gurson criterion.The present work also addresses the effect of the ratio of matrix's eBCS to UCS on the macroscopic strength of porous media.For matrix with distinct values of eBCS and UCS,neglecting the difference between eBCS and UCS would result in an underestimation of the macroscopic strength,especially when the pressure is large.     

The effects of biofilm on the transport of stabilized zerovalent iron nanoparticles in saturated porous media

The transport of stabilized zerovalent iron nanoparticles (nZVI) has recently been the topic of extensive research due to its proven potential as an in situ remediation tool. However, these studies have ignored the effects of biofilms—complex aggregations of bacterial cells and excreted extracellular polymeric substances present in nearly all aquatic systems—on the transport of these particles. This study examines the effects of Pseudomonas aeruginosa (PAO1) biofilm, at a cell concentration similar to that reported for saturated aquifers, on the transport of commercially available, poly (acrylic acid) stabilized nZVI (pnZVI) in 14 cm long columns packed with saturated glass beads at salt concentrations of 1 and 25 mM NaCl. Compared to retention on uncoated columns, in the presence of biofilm the retention of pnZVI increased at higher ionic strength, while ionic strength played no role in retention of these nanoparticles in the absence of biofilm. The Tufenkji-Elimelech correlation equation predicts lower retention of pnZVI on biofilm coated columns compared to uncoated columns due to a lower Hamaker constant, and DLVO energy considerations predict the most favorable attachment to uncoated porous media at higher ionic strength. A steric (polymer-mediated) model that considers the combined influence of steric effects of polymers and DLVO interactions is shown to adequately describe particle retention in columns.     

Fluorescent dye labeled bacteriophages--a new tracer for the investigation of viral transport in porous media: 1. Introduction and characterization

A new method for the study of pathogen transport in porous media is presented. The method is based on conjugation of fluorescent dyes to target bacteriophages and application of the modified bacteriophages for tracer studies. We demonstrate that the relevant transport determining properties of Rhodamine and several fluorescein-labeled phages are practically identical to those of the native bacteriophages. The advantages of the proposed method relative to direct enumeration of bacteriophages by plaque forming unit method, turbidity, fluorescent microspheres, and other alternative tracers are discussed. Notable advantages include simple quantitation by optical methods, unbiased signals even when virus aggregates are formed, and the ability to decouple inactivation kinetics from transport phenomena. Additionally, the signal reflects the removal and transport of the studied microorganism and not a surrogate.