Development of a simulation system for a continuous flow, quiescent, aqueous environment (original) (raw)
Related papers
Water Resources Research, 2000
Suspended particles are a ubiquitous component of aqueous environments and are found over broad ranges of size and density. Particle transport and fate have an important role in the regulation of contaminants and nutrients in natural settings. The mechanisms that control the transport and size of particulate material in solution also play a fundamental role in the successful operation of engineered systems, such as sedimentation ponds and flocculation tanks, as well as flotation and filtering reactors. Adequate modeling of particle transport and aggregation is required for better understanding and prediction of the effects of particulate material in natural aqueous systems, as well as for designing efficient physicochemical processes to deal with suspended solids. In this paper we illustrate how numerical diffusion produced by the use of first-order finite difference schemes can introduce significant errors in the modeling of particle settling in quiescent systems and how this error is compounded when aggregation is considered. To model settling without introducing numerical diffusion, while preserving numerical efficiency, we propose the residence-time scheme, a simple numerical scheme based on the residence time of each size fraction in the elements of the spatial discretization. For the solution of the settling-aggregation equation the alternatingoperator-splitting technique (AOST) is used. The inherent modularity and simplicity of AOST allows smooth incorporation of additional particle transport mechanisms such as mixing, advection, etc.
Significance of Aggregation of Fine Sediment Particles in Their Deposition
Estuarine, Coastal and Shelf Science, 2002
The significance of aggregation processes, by which the properties of suspended fine sediment particles or flocs change during transport, is examined for the simple case of deposition of estuarine sediments in a flume. A multi-class model for aggregation processes is combined with a one-dimensional, unsteady, multi-class sediment transport model to calculate the deposition rate for two flume experiments—one with no
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1997
Laboratory studies have modelled the interaction of Darling River water and a saline groundwater intrusion. Kinetic measurements have shown that the rate determining step in water column clarification is the aggregation of small colloidal particles which then settle rapidly after reaching a critical diameter. Divalent cations (Ca-'+ and Mg 2 ~} are extremely effective in enhancing the rate of clarification by increasing the colloid stability factor. Three different phases have been observed in the cation-mediated removal of iron from solution: (i) rapid coagulation induced by tile initial velocity shear resulting from solution mixing; (ii) a slower second-order iron removal, consistent with conventional aggregation kinetics; and (iii) a decrease in rate after 90% iron removal which is attributed to a lower iron content in the ultrafine colloid fraction. Specific interactions between the divalent cations and the organic coatings on the particles are proposed in order to explain the much higher rate of coagulation than expected on electrostatic grounds when compared with the monovalent Na + and K +. Water column clarification occurred more rapidly in these model laboratory studies than was observed in the Darling River weir pool. Iron removal rates in the river tend to be inhibited by hydrological effects. Turbulence inducing processes are required to mix the dense saline groundwater with the overlying water column and thus may ultimately limit the rate of turbidity reduction.
2010
A new continuous one-dimensional sedimentation model incorporating a new continuous flocculation model that considers aggregation and fragmentation processes was derived and tested. Additionally, a new procedure to model sediment particle size distribution (PSD) was derived. Basic to this development were three different parametric models: Jaky, Fredlund and the Gamma probability distribution (GPD) were chosen to fit three different glass micro-spheres PSDs having average particle sizes of 7, 25 and 35 microns. The GPD provided the best fit with the least parameters. The bimodal GPD was used to fit ten sediment samples with excellent results (< 5% average error). A continuous flocculation model was derived using the method of moments for solving the continuous Smoluchowski coagulation equation with fragmentation. The initial sediment PSD was modeled using a bimodal GPD. This new flocculation model resulted in a new general moments' equation that considers aggregation and fragmentation processes, which is represented by a system of ordinary differential equations. The model was calibrated using a genetic algorithm with initial and flocculated PSDs of four sediment samples and four anionic polyacrylamides flocculants. The results show excellent correlation between predicted and observed values (R 2 > 0.9878). A new continuous one-dimensional sedimentation model that resulted in a scalar hyperbolic conservation law was derived from the well-known Kynch kinematic sedimentation model. The model was calibrated using column tests results with glass micro-spheres particles. Two different glass microspheres particle size distributions (PSDs) were used with average diameters of 7 and 37 microns. Excellent values of coefficient of determination (R 2 > 0.89, except for one test replicate) were obtained for both the small and large glass micro-spheres PSDs. These results suggest that the proposed sedimentation model can be expanded to model the sedimentation process inside a sediment pond.
Particle aggregation in complex aquatic systems
1999
The influence of humate, gallate and salicylate on the surface charge character and particle aggregation of permanently and/or conditionally charged clay and oxide minerals (montmorillonite, kaolinite and aluminium-oxide) was investigated at pH 7-8 in the presence of an indifferent electrolyte. pH-dependent surface charging of minerals were determined by acid-base titration. The pH-and ionic strength dependent particle aggregation was measured in both the absence and presence of organic anions by means of dynamic light scattering (DLS ). Relatively small amount of organic anions, less than one species per nm2, adsorbed on the Al-OH surface sites of minerals induces a significant increase in the colloidal stability of dilute suspensions. Bound organic anions smear out the heterogeneity of surface charge and the differences between the clay and oxide minerals.
Characteristics of Resuspension, Settling and Diffusion of Particulate Matter in a Water Column
Environmental Fluid Mechanics, 2005
Experiments were conducted in order to characterize the distributions of concentrations of suspended particulate matter (SPM) in water columns of lakes and reservoirs. The experiments, in a reduced model of the water column, used a set of oscillating grids. Runs were done with particles denser than water as well as with light particles. The results were in good agreement with analytical solutions for steady-state, and non-steady-state conditions. An approximate analytical solution was derived and found to be in agreement with the full solution. The threshold for resuspension was measured, and characterized in terms of a modified Shields parameter, which is appropriate to a zero-shear environment. All experiments showed that the distribution of SPM exhibited a layer near the bottom that is thought to be analogous to the benthic nepheloid layer (BNL) observed in larger lakes. The thickness of the nepheloid layer increases with the turbulence intensity.
Deep Sea Research Part I: Oceanographic Research Papers, 2004
The largest decrease in the particle vertical flux occurs in the mesopelagic zone where particles are transformed by biological and physical mechanisms. Particle size distributions provide important clues into those processes affecting particle transformations in this region. We have studied them using an inter-annual data set showing the evolution of particle size distributions between 100 and 1000 m, comparing them to results from a series of size-resolved models of particle dynamics that include physical coagulation and biological remineralization. The formulation that best fits the observations consists of a combination of settling, microbial activity and zooplankton feeding. The calculated particulate organic carbon losses to microbial activity and zooplankton feeding are consistent with independent estimates of these rates. The model shows that it is possible to predict the particle size distribution at 1000 m depth knowing the particle size distribution at 100 m depth and the rates of transformation in the mesopelagic. The mesozooplankton appears to be important in decreasing the high flux of large particles in the upper midwater zone, microbes becomes more important in the deeper midwater zone as zooplankton become rarer. The results suggest that the mesozooplankton have a much greater effect on particle flux than the macrozooplankton. Their importance requires the mesozooplankton to feed preferentially on large settling particles, probably using remote detection. The present work shows that using particle size spectra is a useful way to understand the transformation of the vertical flux of element in the midwater zone. However, most of the assumptions on particle properties and processes are based on surface studies and more data from the midwater zone are needed to confirm the hypotheses. The model allows us to formulate crucial questions regarding particle dynamics in the midwater zone. r
Aggregation rates of natural particle populations
Water Research, 2001
}In this paper an experimental approach of aggregation in natural suspensions is presented. The suspensions are organic-matter-rich waters sampled in a brook which drains peat areas. The aggregation was conducted on raw samples in three different experiments lasting from 2 to 8 days. The particle size distribution (PSD) in the 0.5-10 mm size range was followed with a laser sizer and appeared to be almost constant along the whole experiment duration. Nevertheless, the volume of particles larger than 10 mm increased steadily, showing that aggregation occured. This appeared to be the consequence of a steadystate aggregation which allowed the removal of the whole particle set within a day. The use of an aggregation model adapted to calculations on PSD allowed estimation of the aggregation efficiency for such suspensions.
Settling classes for fine suspended particles
Comptes Rendus Mécanique, 2006
The modelling of pollutant transfer in freshwater systems can be refined by considering the heterogeneities of the sedimentary dynamics and of the chemical reactivities of fine suspended particles. One of the first steps is the fractionation of these fine particles into effective settling classes. Although several methods exist, most of them are based on either granulometric considerations and/or arbitrary threshold criteria. This article presents the bases of an experimental method focusing on the direct measurement of the settling velocities without considering the granulometry and/nor any threshold criteria. The experimental work consists in recording the temporal evolution of the vertical distribution of the suspended solid concentration in a settling tank. A mathematical analysis provides the number of particle groups, and the mass contribution and the settling velocity for each This procedure is described and applied for validation, as a first step, to calibrated suspensions. Additional work is needed for a further analysis of the physical constraints involved in the model, as well as for more extensive experimental validation. To cite this article: C. Brach-Papa et al.,