Single Collector Efficiency Research Articles

Treatment of Oily Wastewater by Fibrous Coalescer Process: Stage Coalescer and Model Prediction

The coalescer process is one of the methods for oily water treatment by increasing the oil droplet size in order to enhance the separating velocity and thus effective separation. However, the presence of surfactants in an oily emulsion can limit the obtained mechanisms due to the small oil size related with stabilized emulsion. In this regard, the purpose of this research is to improve the efficiency of the coalescer process for treating the stabilized emulsion. The effects of bed types, bed height, liquid flow rate and stage coalescer (step-bed) on the treatment efficiencies in term of COD values were studied. Note that the treatment efficiency obtained experimentally was estimated by using the COD values and oil droplet size distribution. The study has shown that the plastic media has more effective to attach with oil particles than the stainless one due to their hydrophobic properties. Furthermore, the suitable bed height (3.5 cm) and step bed (3.5 cm with 2 steps) were necessary in order to well obtain the coalescer performance. The application of step bed coalescer process in reactor has provided the higher treatment efficiencies in term of COD removal than those obtained with classical process. The proposed model for predicting the area under curve and thus treatment efficiency, based on the single collector efficiency (ηT) and the attachment efficiency (α), provides relatively a good coincidence between the experimental and predicted values of treatment efficiencies in this study.

A Correlation for the Collector Efficiency of Brownian Particles in Clean-Bed Filtration in Sphere Packings by a Lattice-Boltzmann Method

In this paper, we develop a new correlation for the clean-bed filter coefficient (lambda0) for Brownian particles, for which diffusion is the main deposition mechanism. The correlation is based on numerical Lattice-Boltzmann (LB) simulations in random packings of spheres of uniform diameter. We use LB methods to solve the Navier-Stokes equation for flow and then the advection-diffusion equation for particle transport. We determine a correlation for an "equivalent" single-collector diffusion efficiency, etaD, so that we can compare our predictions to "true" single-collector correlations stemming from unit-cell modeling approaches. We compared our new correlation to experiments on the filtration of latex particles. For small particle diameters, 50 nm < dp < 300 nm, when gravity and interception are negligible, our correlation for etaD predicts measurements better than unit-cell correlations, which overestimate etaD. The good agreement suggests that the representation of three-dimensional transport pathways in porous media plays an important role when modeling transport and deposition of Brownian particles. To model larger particles, for which gravity and interception are important too, we build a correlation for the overall single-collector efficiency eta0 by adding corresponding etaG and nI terms from unit-cell correlations to our etaD model. The resulting correlation predicts experiments with latex particles of dp > 300 nm well.

A new method to evaluate polydisperse kaolinite clay particle removal in roughing filtration using colloid filtration theory

Previous application of colloid filtration theory to roughing filtration has not considered a reliable method for determining a representative attachment factor for a polydisperse suspension (of constant particle density). Establishment of such a method would broaden the application of trajectory modelling in roughing filtration, and progress the development of a comprehensive database of attachment factors and surface charge potentials for various particle and fluid types. This study establishes a methodology for the application of colloid filtration theory to roughing filtration and incorporates recent advancements in theoretical single-collector efficiency. A polydisperse kaolinite clay suspension was passed through a series of four gravel upflow roughing filters and removal efficiencies were calculated. Both the classical and Tufenkji and Elimelech's more recent correlation equations were used to calculate theoretical single-collector efficiencies and associated attachment factors for three different filter media sizes, flow rates, and suspended solids concentrations (0.137±0.023). The use of Tufenkji and Elimelech's modified correlation equation resulted in reduced variability in the estimation of theoretical single-collector efficiencies.

Revisiting the Cape Cod Bacteria Injection Experiment Using a Stochastic Modeling Approach

Bromide and resting-cell bacteria tracer tests conducted in a sandy aquifer at the U.S. Geological Survey Cape Cod site in 1987 were reinterpreted using a three-dimensional stochastic approach. Bacteria transport was coupled to colloid filtration theory through functional dependence of local-scale colloid transport parameters upon hydraulic conductivity and seepage velocity in a stochastic advection-dispersion/attachment-detachment model. Geostatistical information on the hydraulic conductivity (K) field that was unavailable at the time of the original test was utilized as input. Using geostatistical parameters, a groundwater flow and particle-tracking model of conservative solute transport was calibrated to the bromide-tracer breakthrough data. An optimization routine was employed over 100 realizations to adjust the mean and variance of the natural-logarithm of hydraulic conductivity (InK) field to achieve best fit of a simulated, average bromide breakthrough curve. A stochastic particle-tracking model for the bacteria was run without adjustments to the local-scale colloid transport parameters. Good predictions of mean bacteria breakthrough were achieved using several approaches for modeling components of the system. Simulations incorporating the recent Tufenkji and Elimelech (Environ. Sci. Technol. 2004, 38, 529-536) correlation equation for estimating single collector efficiency were compared to those using the older Rajagopalan and Tien (AIChEJ. 1976, 22, 523-533) model. Both appeared to work equally well at predicting mean bacteria breakthrough using a constant mean bacteria diameter for this set of field conditions. Simulations using a distribution of bacterial cell diameters available from original field notes yielded a slight improvement in the model and data agreement compared to simulations using an average bacterial diameter. The stochastic approach based on estimates of local-scale parameters for the bacteria-transport process reasonably captured the mean bacteria transport behavior and calculated an envelope of uncertainty that bracketed the observations in most simulation cases.

Influence of particle concentration on initial collection efficiency and surface coverage in porous media filtration

Four sizes (0.095, 0.53, 1.0 and 2.01 µm) of polystyrene latex particles were used to prepare monodispersed suspensions at three different ionic strengths (103,10-2.5 and 10-2 M KCl). Filtration experiments were conducted using those suspensions in a filter column with glass beads as porous medium. The filter bed depth and the filtration velocity were kept at 5 cm and 1 m/h, respectively. When suspensions with equal mass concentrations (0.2 mg/L) or equal surface area concentrations (0.12 cm2/mL) were filtered through the system, the largest particles exhibited higher initial single collector efficiency, ⪯. The difference between the C of largest particles and the smaller particles was prominent for suspensions with equal surface area concentrations at higher ionic strengths. The collision efficiency,α of those particles exhibits higher values at higher ionic strengths. Both at equal mass concentration and equal surface area concentration,α is only slightly dependent on particle sizes when compared to its dependence on ionic strength. Further, it was found that the specific surface coverage was similar for 0.095 µm, 0.53 µm and 1.0 µm particles during the transient stage of filtration at any ionic strength when the surface area concentrations of those suspension were equal.

Response to Comment on “Correlation Equation for Predicting Single-Collector Efficiency in Physicochemical Filtration in Saturated Porous Media”

Response to Comment on “Correlation Equation for Predicting Single-Collector Efficiency in Physicochemical Filtration in Saturated Porous Media”

Comment on “Correlation Equation for Predicting Single-Collector Efficiency in Physicochemical Filtration in Saturated Porous Media”

Comment on “Correlation Equation for Predicting Single-Collector Efficiency in Physicochemical Filtration in Saturated Porous Media”

Capture of water-borne colloids in granular beds using external electric fields: improving removal of Cryptosporidium parvum

Suboptimal coagulation in water treatment plants often results in reduced removal efficiency of Cryptosporidium parvum oocysts by several orders of magnitude (J. AWWA 94(6) (2002) 97, J. AWWA 93(12) (2001) 64). The effect of external electric field on removal of C. parvum oocysts in packed granular beds was studied experimentally. A cylindrical configuration of electrodes, with granular media in the annular space was used. A negative DC potential was applied to the central electrode. No coagulants or flocculants were used and filtration was performed with and without application of an electric field to obtain improvement in removal efficiency. Results indicate that removal of C. parvum increased from 10% to 70% due to application of field in fine sand media and from 30% to 96% in MAGCHEM media. All other test particles (Kaolin and polystyrene latex microspheres) used in the study also exhibited increased removal in the presence of an electric field. Single collector efficiencies were also computed using approximate trajectory analysis, modified to account for the applied external electric field. The results of these calculations were used to qualitatively explain the trends in the experimental observations.

Correlation equation for predicting single-collector efficiency in physicochemical filtration in saturated porous media.

A new equation for predicting the single-collector contact efficiency (eta0) in physicochemical particle filtration in saturated porous media is presented. The correlation equation is developed assuming that the overall single-collector efficiency can be calculated as the sum of the contributions of the individual transport mechanisms--Brownian diffusion, interception, and gravitational sedimentation. To obtain the correlation equation, the dimensionless parameters governing particle deposition are regressed against the theoretical value of the single-collector efficiency over a broad range of parameter values. Rigorous numerical solution of the convective-diffusion equation with hydrodynamic interactions and universal van der Waals attractive forces fully incorporated provided the theoretical single-collector efficiencies. The resulting equation overcomes the limitations of current approaches and shows remarkable agreement with exact theoretical predictions of the single-collector efficiency over a wide range of conditions commonly encountered in natural and engineered aquatic systems. Furthermore, experimental data are in much closer agreement with predictions based on the new correlation equation compared to other available expressions.

Kinetic modeling of virus transport at the field scale

Bacteriophage removal by soil passage in two field studies was re-analyzed with the goal to investigate differences between one- and two-dimensional modeling approaches, differences between one- and two-site kinetic sorption models, and the role of heterogeneities in the soil properties. The first study involved removal of bacteriophages MS2 and PRD1 by dune recharge, while the second study represented removal of MS2 by deep well injection. In both studies, removal was higher during the first meters of soil passage than thereafter. The software packages HYDRUS-1D and HYDRUS-2D, which simulate water flow and solute transport in one- and two-dimensional variably saturated porous media, respectively, were used. The two codes were modified by incorporating reversible adsorption to two types of kinetic sites. Tracer concentrations were used first to calibrate flow and transport parameters of both models before analyzing transport of bacteriophages. The one-dimensional one-site model did not fully describe the tails of the measured breakthrough curves of MS2 and PRD1 from the dune recharge study. While the one-dimensional one-site model predicted a sudden decrease in virus concentrations immediately after the peaks, measured data displayed much smoother decline and tailing. The one-dimensional two-site model simulated the overall behavior of the breakthrough curves very well. The two-dimensional one-site model predicted a more gradual decrease in virus concentrations after the peaks than the one-dimensional one-site model, but not as good as the one-dimensional two-site model. The dimensionality of the problem hence can partly explain the smooth decrease in concentration after peak breakthrough. The two-dimensional two-site model provided the best results. Values for k att2 and k det2 could not be determined at the last two of four monitoring wells, thus suggesting that either a second type of kinetic sites is present in the first few meters of dune passage and not beyond the second monitoring well, or that effects of soil heterogeneity and dimensionality of the problem overshadowed this process. Variations between single collector efficiencies were relatively small, whereas collision efficiencies varied greatly. This implies that the nonlinear removal of MS2 and PRD1 is mainly caused by variations in interactions between grain and virus surfaces rather than by physical heterogeneity of the porous medium. Similarly, a two-site model performed better than the one-site model in describing MS2 concentrations for the deep well injection study. However, the concentration data were too sparse in this study to have much confidence in the fitted parameters.

Deposition Behavior of Latex Particles In Filtration Process Through Glass Packed Column

AbstractThe deposition behavior of colloids from a flowing suspension onto a solid collector surface infiltration process was observed by conducting column experiments with polystyrene latex particlesand glass beads packed columns. From the observed particle breakthrough curves, single collectorefficiencies were calculated. By comparing the single collector efficiency obtained in the columnexperiment with the existing approximate expression, the effects of flow velocity on the depositionbehavior was discussed.

Depth Filtration: Fundamental Investigation through Three-Dimensional Trajectory Analysis

A mathematical model (array of spheres or AOS Model) of aqueous depth filtration was developed using trajectory analysis performed on a porous media model comprised of a face-centered cubic packing of spheres. To extend removal efficiency predictions beyond the grain-size scale and take into account the presence of densely and sparsely packed regions in an actual filter bed, a parallel deficit porosity compensation scheme was developed and applied. A correlation for single collector efficiency was developed from trajectory results and, using the parallel deficit porosity compensation scheme, compared to an existing model and experimental results. Although the model discussed herein was developed with the intent of advancing the understanding of depth filtration, this work offers tools for investigating and insights into particle fate and transport in other circumstances, e.g., groundwater aquifers. This model represents the first use of a porous media model that explicitly accounts for grain contact points for trajectory modeling of aqueous depth filtration. Particle collection within the model was strongly associated with grain contact points, a phenomenon due largely to hydrodynamic forces “funneling” particles to trajectories coincident with grain contact points. In comparison to previous trajectory models, this model is less sensitive to particle size and filtration rate and much less sensitive to surface chemistry than other currently available models. At moderate to high filtration rates (on the order of 3.7 mm/s or 5.4 gpm/ft2), the AOS model represented well experimental data for removal of particles less than 5 μm. At lower filtration rates and larger particle sizes, the AOS model tends to overpredict particle removal.

Shadow Effect and Filtration Efficiency of a Granular-Bed Filter

The filtration efficiency of a granular-bed filter is classically computed under the assumption that the collected particles are completely remixed after each layer of collectors, and thus the single-collector efficiency model may be repeatedly applied to each and every layer. Comparisons of total filter efficiencies obtained experimentally for filters that differ only in their respective lengths indicate this assumption to be wrong. Filters of different lengths yield different values for the single-collector efficiencies when classically checked. The present investigation examines the shadowing affect of one layer on the performance of the next one, taking into account the fact that a region swept by a collector may include parts already depleted of particles by a previous collector. Since the details of the construction of the granular-bed filter are in general not known, there seems to be no deterministic way to formulate the distribution of particle-free regions in the gas behind each collector layer. The distribution is therefore assumed Gaussian, with a standard deviation computed to fit the experimental data. Available experimental data indicate that this investigation indeed yields one single-collector efficiency for filters which differ only by their lengths. For standard deviations which exceed 0.5 the present investigation approaches asymptotically the classical theory; i.e., the shadow effect becomes negligible.

Effects of Cationic Polyelectrolytes on the Removal of Suspended Particulates During Direct Filtration

This research investigated the important parameters influencing the degree of particulate removal from low turbidity water in a configuration that included rapid mixing followed by filtration. The varied parameters were rapid‐mixing velocity gradient, cationic polyelectrolyte type, and polyelectrolyte dosage. The cationic polyelectrolytes were characterized for molecular weight by membrane osmometry, light scattering, and high performance liquid chromatography. The filtration kinetics variables, including maximum depth‐averaged singlecollector efficiency and specific deposit, were used to characterize the efficiency of particulate removal for each of 72 filter runs. Statistical analyses demonstrated that the choice of polyelectrolyte was the only significant factor. Additionally, volume size distribution analyses of particle count data from in‐depth samples in the filter demonstrated that the polyelectrolyte configuration may be critical for adsorption of polyelectrolytes to particulates and media in filtration.