Number Of Flocs Research Articles

Using FBRM to investigate the sewage sludge flocculation efficiency of cationic polyelectrolytes

Polyelectrolyte flocculation is a commonly used method for sewage sludge conditioning. The rate and extent of water removal from the flocculated sludge depends on the properties of the polyelectrolytes. This study investigates the flocculation performance of four different cationic polyelectrolytes using an in-situ laser probe which uses focused beam reflectance measurements (FBRM). It is used to characterise the floc number and size distribution of the flocculated sludge at various polyelectrolyte doses. Results show that the FBRM technique is very successful in tracking the change in particle population and chord lengths during the sludge flocculation process. The FBRM offers an alternative method for optimising the flocculation system in both selecting the flocculant and determining its optimum dose. Both the reduction in particle count for particles of less than 10 mum and the flocculation efficiency defined from the amount of the original sludge distribution remaining after flocculation correlate well with dewatering performance.

Particle trapping in stratified estuaries: consequences of mass conservation

Estuarine turbidity maxima (ETM) can retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities in bed processes. We define a parameter space descriptive of ETM water column particle trapping processes through a scaling analysis of the local and integral SPM balances. There are six primary non-dimensional parameters for the large particles or aggregates that are typically trapped in an ETM. Rouse numberP, the ratio of settling velocityW S to the shear velocityU *, describes the material trapped in the ETM in terms of the local vertical balance between vertical mixing and aggregate settling. Advection numberA = PDU/UT scales the landward transport of SPM in terms of flood-ebb velocity difference (ΔU; the internal asymmetry) and maximum tidal current (U T ). Supply number Sr =PU r /U t defines SPM supply and removal (U r is river flow). Changes in the estuarine inventory of SPM are described in terms of a Trapping EfficiencyE, a ratio of peak ETM concentration to fluvial or marine supply concentration. The effects of aggregation and disaggregation in the integral dynamic balance are quantified by a Floc number Θ = Φ/Г that describes the balance of aggregation (Φ) and disaggregation (Г). The balance between erosion and deposition at the bed is described by the Erosion number Π = Ψ/Ω, the ratio of erosion (Ψ) to deposition(Ω). The non-dimensional, integral SPM conservation equation is then used to examine steady and unsteady particle trapping scenarios, including adjustments to a change in river flow and to a neap-spring transition in salinity intrusion and stratification.

Particle trapping in stratified estuaries: Application to observations

Estuarine turbidity maxima (ETM) retain suspended particulate matter (SPM) through advection, settling, aggregation, and nonlinearities in bed processes, but the relative importance of these processes varies strongly between systems. Observations from two strongly advective systems (the Columbia and Fraser Rivers) are used to investigate seasonal cycles of SPM retention and the effects of very high flows. Results for the Fraser and Columbia plus literature values for 13 other estuaries illustrate the applicability of scaling parameters and the response of ETM phenomena to a range of river flow (U r ) levels and tidal forcing. The most efficient trapping (represented by Trapping EfficiencyE, the ratio of maximum ETM concentration to the source SPM concentration) occurs for low ratios of river flow to tidal current amplitude (UT), represented by low values of the Supply number Sr.E in the Columbia is found to be maximal in a null zone where advection or tidal asymmetry (represented by Advection numberA) is weak(A ∼ 0). The ratio of aggregation to disaggregation (the Floc number Θ) is maximal on neap tides, while the ratio of erosion to deposition (the Erosion number P) is maximal on spring tides. The ratio of settling velocity to vertical mixing (Rouse numberP) is relatively constant in the Columbia ETM(P ∼ 0.7), because particle settling velocity and turbulence levels adjust together. Assuming that this result applies broadly, scaling variables and data are combined to express ETM properties in terms of the friction velocity (U*),U r , andU T , allowing a considerable simplification of the parameters used to describe ETM.

Techniques for Automated Measurement of Floc Properties

Abstract This paper summarizes the development of equipment and techniques used for automated capture of floc images and measurement of floc properties. Methods for floc analysis are described which may be used equally well in the field or in the laboratory. The Matlab Image Processing Toolbox is used as a front end for applying several algorithms designed to clarify the images and measure the flocs. An iterative function provides threshold values to separate flocs from varying background light conditions in a stable and repeatable manner. The methods described can provide real-time analysis without user intervention. Matlab and IDL routines have been designed to measure settling velocity. The use of totally automated tracking over measurements made by a graphical user interface approach results in vastly more efficient measurements. The automated method also provides better data for very small and very slow-moving flocs. The graphical user interface approach, on the other hand, does not lead to some of the errors associated with the automated tracking. Both methods provide similar information about floc number, size, shape, and settling velocity, which can be used to calculate properties such as excess density, porosity, and fractal dimensions. Finally, kernel density estimation is introduced as a method to make meaningful interpretations from large amounts of highly variable data.

Effect of floc structure on the rate of Brownian coagulation

A modified expression for the Smoluchowski solution for the temporal evolution of the number concentration of flocs subject to Brownian coagulation is proposed, taking into account the effect of the growth of floc structure. In the proposed equation, the effect is expressed as a decrease of free volume in the liquid phase due to the increase of effective floc volume in accordance with the progress of coagulation. The validity of the proposed equation was tested by coagulation experiments using polystyrene latex particles. Direct counting of the number of flocs under microscopy provided accurate data on the temporal evolution of the number concentration of flocs. The obtained rate gradually increases in accordance with the growth of floc structure. This behavior agreed exactly with the prediction based on the proposed equation.

Characterisation, scaling and analysis of steady state floc size distribution using a mass balance approach

Research Article| August 01 2006 Characterisation, scaling and analysis of steady state floc size distribution using a mass balance approach D. H. Bache; D. H. Bache 1Department of Civil Engineering, University of Strathclyde, Glasgow, G4 ONG, UK Fax: +44 141 553 2066; E-mail: d.bache@strath.ac.uk Search for other works by this author on: This Site PubMed Google Scholar E. Rasool E. Rasool 2Scientific Services, Scottish Water, 419 Balmore Rd, Glasgow, G22 6NU, UK Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2006) 55 (5): 335–356. https://doi.org/10.2166/aqua.2006.059 Article history Received: September 18 2005 Accepted: April 11 2006 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation D. H. Bache, E. Rasool; Characterisation, scaling and analysis of steady state floc size distribution using a mass balance approach. Journal of Water Supply: Research and Technology-Aqua 1 August 2006; 55 (5): 335–356. doi: https://doi.org/10.2166/aqua.2006.059 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex A framework is developed for describing the steady state floc size distribution Ψ(u) in terms of a scaling ratio u = d/dL in which d is a representative aggregate diameter and dL, the corresponding arithmetic average value across the distribution. Flocs were treated as objects of simple fractal structure, such that the floc solids mass (m) complied with the scaling m∝dD in which D is the fractal dimension. From integration of the solids mass across the size distribution, it was shown that the overall solids concentration (M) followed the dependence M∝NA′dDL S(D) in which N is the number of flocs per unit volume, A′ is a packing factor and S(D) a shape factor. Theory was developed to enable estimation of the foundation size distribution for situations in which data on the smallest floc sizes was missing as a result of the lower resolution limit of a measuring system. The framework was used to analyse five data sets displaying different features. Under conditions of varying shear, it was found that the mass scaling dependence shown above could not be explained on the basis of fixed values of A′ or D; this was attributed to a kinetic dependence of the floc solids concentration on shear and beyond the impact of shear on floc size. For the data sets analysed it was shown that the distribution responds to changes in shear and M in a complex way and there were several pointers to the lack of self-similarity. distribution, floc, fractal, mass, shear, size This content is only available as a PDF. © IWA Publishing 2006 You do not currently have access to this content.

Kinematic assessment of floc formation using a Monte Carlo model

A simple stochastic model is proposed to simulate floc formation due to simultaneous aggregation and breakage processes. The model is based on the constant-number Monte Carlo method where the number of flocs is kept constant during simulations. To produce equilibrium floc-size distributions, it uses established models of flocculation and new simple formulations of breakage probability and of the probability of producing fragments of a given size from broken flocs. The concept of fractal geometry is used to describe the geometry of flocs. The maximum size of flocs allowed, the median size of component particles, and their density are the main inputs needed to simulate floc formation. Simulated steady-state floc-size distributions were compared with field data observed at different locations, and good agreement was obtained. Dimensional analysis applied to measured and simulated data revealed that floc-size distributions are self-similar and can be described by the same function, regardless of the conditions of their formation.

QUANTIFICATION AND MODELING OF AGGREGATE BACTERIAL GROWTH IN SUSPENSION: IMPLICATIONS FOR BACTEREMIA

Bacteremia is a central event in the pathogenesis of sepsis. While much is known clinically of blood stream infections, little is known of bacterial life in the bloodstream. We have observed that Klebsiella pneumoniae in liquid media tend to grow in multicellular aggregates, or flocs. Hypothesizing that bacterial floc formation could have significant importance to the proliferation and clearance of bacteria from the bloodstream, we studied floc formation using an in vitro model. K. pneumoniae strain 43816 (a mouse pathogen) was grown in minimal media with 1% glucose at 37°C on a platform orbiting at 100 rpm. Floc volume was quantified with a Coulter counter using 5- to 400-femtoliter particle windows (with the average volume of a single bacterium ~ 5 fL). Growth dynamics were modeled using both log-linear statistical and partial differential equation (PDE) mechanistic models. Confocal laser scanning microscopy (CLSM) was used to study floc structure. Under the conditions studied, flocs from Kp 43816 formed quickly. Log-linear modeling revealed the predicted number of flocs of volume v (in fL) at time t (in minutes) was 10^(5.49+0.19t-(2.10 log(v))), with the p value for each parameter < 0.0001. The PDE model captured significantly more detail of growth and suggested that aggregate formation was due to bacterial proliferation rather than bacterial collisions. Digital image analysis of CLSM cross sections indicated that ~25% of floc volume was comprised of bacteria with the remaining volume being extracellular matrix. Analysis of 3 clinical blood isolates revealed similar behavior. CONCLUSION: K. pneumoniae, a common bloodborne pathogen, forms multicellular structures when grown in conditions mimicking growth in blood. These structures may achieve a size too large either to be phagocytosed or to pass through some capillaries. Future studies of bacterial transit in flowing blood should consider multicellular, and not just singlecellular, architecture.

Floc size distribution in a stirred suspension

This paper focuses on the distribution of alumino-humic flocs found in a stirred suspension. Distributions were scaled using the transformation u = d/dL in which d is floc diameter and dL its arithmetic mean value and fitted by a gamma distribution. Flocs were treated as monofractal with solids mass concentration specified by C = A'rhos (d/do)D-3 in which A' is a packing coefficient, rhos the density of the floc solids, D the fractal dimension and do a reference size. It was shown that the overall solids concentration (M) complies with the dependence M proportional to NA'dDL-S(D) in which N is the number of flocs per unit volume and S(D) a distribution moment. Initial estimates of A' and D were obtained from analysis of floc sedimentation behaviour. From knowledge of the base parameters, the calculated value of M did not match the measured M and varied with shear. This was attributed to a kinematic influence on C over and beyond changes associated with the response of dL to shear. Issues of self-similarity were examined and it was concluded that distributions did not display strict self-similarity. Data are provided on the size distribution found in the flocculators of a treatment works at full scale.

Flocculation of biological cells: Experiment vs. theory

AbstractFlocculation of biological cells is important in the biotechnology industry, as it could lead to improved efficiencies for bioreactor harvesting operations such as microfiltration. Experimental studies for flocculation of yeast and CHO cells using cationic polyelectrolytes suggest the existence of a steady‐state, self‐similar floc size distribution. The experimentally determined floc size distributions were modeled using a population balance approach. For flocculated yeast suspensions, the variation of the floc volume fraction with dimensionless particle diameter is predicted by the population balance model assuming a binary breakage distribution function. However, the variation of floc number fraction with dimensionless particle diameter is better predicted assuming a log normal fragment distribution function probably due to the presence of submicron‐sized yeast cell debris. For CHO cell flocs, the floc volume and number fractions are predicted using a log normal fragment distribution function. CHO cells are far more fragile than yeast cells. Thus, individual CHO cells in a CHO cell floc can lyse leading to the formation of a number of small particles.

Brownian dynamics simulation of linear chain growth

Growth of linear chains is simulated by the technique of Brownian dynamics. The influence of the initial volume fraction of particles on the rate of the process and the structure of the chains is studied. Results show that aggregation is swift at the beginning of the process and very slow at the end. This is due to the decrease of the number of flocs in solution and the decrease in the efficiency of collisions when the degree of aggregation increases. The polydispersity of the system increases during aggregation and reaches a maximum value when the reaction is 96% complete. This increase is greater at higher concentrations. Results indicate that for lower concentrations aggregate growth is principally by reactive collision between aggregates of similar molecular weight, while for higher concentrations there is a relatively high fraction of reactive collisions between aggregates with very different molecular weights. The concentration effect on the structure of the chains is studied, evaluating the fractal dimensions of the chains. When the concentration increases there is a transition from very open structures (fractal dimension 1.76) to very tangled structures, where chains are collapsed (fractal dimension 3).

The effect of dissolved oxygen concentration on the structure, size and size distribution of activated sludge flocs

The variations in activated sludge floc structure, size and size distribution were studied for different dissolved oxygen (DO) concentrations in pilot scale completely mixed reactors. The size distribution by volume for flocs larger than about 10 μm fitted well to log–normal distribution functions. No clear relationship between DO concentration and average floc diameter could be found; there was only a trend towards larger flocs at higher DO concentrations. Lower DO concentrations (0.5–2.0 mg/l) produced sludge with poorer settling properties and higher turbidities of the effluent than higher DO concentrations (2.0–5.0 mg/l). The main reasons to the deteriorated settling properties were excessive growth of filamentous bacteria and the formation of porous flocs. Alternating aerobic and anaerobic conditions (1–4 h) did not affect the settling properties to a large extent. The turbidity increased significantly during the anaerobic period and decreased during the aerobic period. The supernatant was also analysed with a particle analyser. During alternating aerobic/anaerobic conditions, the proportion of smaller flocs (2–20 μm) increased gradually during the anaerobic periods. Directly after that the oxygen supply was turned on, the number of small flocs decreased. In most of the measurements, more than 80% of the number of flocs in the supernatant were smaller than 2 μm. The size distribution of small flocs could best be fitted to power functions. The number of flocs in the supernatant could relatively well be related to the turbidity.

Relationship between the amount of fine particles and the maximum size of flocs in a weight equivalent suspension of quartz and fluorite

Flocculation is largely utilized as an engineering technique in mineral processing practice and the phenomena of fine particles in aqueous suspension can be understood qualitatively through the DLVO theory. However, a clear quantitative theory on the mechanism has not yet been established. Therefore, we studied the flocculation phenomena using quartz and fluorite particles which are negatively and positively charged in aqueous suspension. In this study, experiments were carried out using three quartz samples and three fluorite samples which have different amount of particles smaller than 2.31 μm to clarify the relationship between the amount of fine particles and the maximum size of flocs in aqueous suspension. Quartz particles do not flocculate at all pH values in spite of the variation of the amount of fine particles in the aqueous suspension, while −2.31 μm fluorite particles flocculate into flocs of 13.1–4.63 μm at pH over 10. In addition, an increase in the number of fine particles causes an increase in not the size but the number of flocs. In the case of a weight equivalent mixture of quartz and fluorite particles, hetero-flocculation occurs clearly at pH below 10, and it can be observed that an increase in the number of fine particles influences both the floc size and the number of flocs.

Kinetic models of suspension flocculation by polymers

A comparison of mathematical models that describe the kinetics of flocculation of a suspension is presented. The models enable us to describe the process over a wide time interval, including late stages, and to find values of the kinetic constants. This provides the possibility of calculating the relationships of the floc number in the system and of the number of primary particles in a floc with time and with the initial coverage of the particle surface with flocculant. The agreement between the kinetic models and experimental data for the flocculation of polystyrene latex by poly(methyl vinyl pyridine) is shown. The model that takes both the changing floc surface coverage with polymer during flocculation and the floc break-up into account, has the highest accuracy.

RHEOLOGICAL BEHAVIOUR OF COCOA DISPERSIONS

ABSTRACTThe steady‐shear viscosities of cocoa mass and cocoa suspensions were measured over a wide range of temperature and cocoa powder content. The effects of gasification, moisture and lecithin contents were also investigated. The viscosity of cocoa mass followed the Quemada or the Casson model. Both viscosity and yield stress decreased with increasing temperature. Degasification also lowered the viscosity and yield stress. The viscosity of concentrated cocoa suspension increased with increasing powder content and exhibited shear‐thinning behaviour, and followed the Kreiger and Dougherty model. While the relative intrinsic viscosity was nearly constant, the maximum volume fraction increased with increasing shear stress or shear rate. Addition of moisture in suspension increased the viscosity due to partial gelation of starch; while addition of lecithin decreased the viscosity due to the lesser number of flocs in the suspension.

The behaviour of floc in the flocculation of kaolinite clay

Several experimental runs were performed to investigate the effect of kaolinite particle size, flocculation time, velocity gradient, coagulants dose and initial turbidity on the solid removal and floc size or floc formation of suspended solid. The coagulants used were alum, polyelectrolyte (cationic) or a combination of both. Different classifications of clay particles are used in the present work of grade less than 10, 20 and 40 μm. The particle size of 10 μ at 200 NTU initial water turbidity was used to study the effect of flocculation time, (1-20 min) on floc formation size and flocs number at optimum velocity gradient. The size distribution of flocs was studied as a function of kaolinite concentration in the range 1-3 mg/1 at 20 min flocculation time in case of alum and polyelectrolyte. The results are presented graphically by three-dimensional and contour plots showing the floc number as a function of coagulant dose and flocculation time. The results are also plotted to show the required turbidity as a function of velocity gradient and flocculation time at optimum coagulant dose to locate the overall optimum working conditions. It is found from various experimental results that floc size or floc formation and growth are the principal criteria that effect the flocculation process.

Comparison of Polyferric Sulphate with Other Coagulants for the Removal of Algae and Algae-Derived Organic Matter

This paper is concerned with the performance of a relatively new form of metal-iron coagulant, Polyferric Sulphate (PFS), which has received very little research attention to date. Laboratory experiments have been undertaken in which the coagulation performance of PFS, Ferric sulphate, Aluminium sulphate and Poly aluminium chloride have been studied using ‘model' waters containing single cultures of algae (Anabaenaflos-aquae and Asterionetta formosa) and other ‘model' waters prepared by mixing aquatic humic substances with Asterionella formosa at different concentration ratios. Physico-chemical variables such as colloid charge, floc number concentration and size distribution, DOC concentration and turbidity, have been determined to quantify treatment performance. The performance of PFS was found to be superior to the other coagulants and this was believed to be due to the presence of more highly charged cation species. For all coagulants there was an approximate stoichiometry between coagulant dose and the dissolved organic carbon concentratioa

Simulation of floe breakage in a batch-stirred tank

The breakage of flocs in a lean, batch-stirred apparatus is modeled by the Monte Carlo simulation approach based on the conservation of primary particles. The fractal structure of floc results in a decrease in both its mass and volume when breakage occurs. The characteristics of the dynamic phenomenon under consideration should be described through the following information: (i) the total number of flocs, (ii) the total volume of the dispersed-phase entities, and (iii) the cumulative number floc size distribution (FSD).

Equilibrium state of aggregation in suspensions comprising linear clusters

The final state of aggregation in a suspension containing nonbranching, one-dimensional (linear) flocs is investigated. Allowing coagulation to occur at a finite secondary minimum of magnitudeV* rather than the infinite primary well, it is realized that the system eventually reaches steady state where a relatively large number of flocs coexist at equilibrium. It is shown that, under this condition, the number of flocs¯N expected to result is exponentially related to −V* and directly proportional to\(\sqrt {N_0 } \), whereNo is the initial number of individual particles in the suspension.

The behaviour of floc in the flocculation of kaolinite clay

Several experimental runs were performed to investigate the effect of kaolinite particle size, flocculation time, velocity gradient, coagulants dose and initial turbidity on the solid removal and floc size or floc formation of suspended solid. The coagulants used were alum, polyelectrolyte (cationic) or a combination of both. Different classifications of clay particles are used in the present work of grade less than 10, 20 and 40 μm. The particle size of 10 μm at 200 NTU initial water turbidity was used to study the effect of flocculation time, (1-20 min) on floc formation size and flocs number at optimum velocity gradient. The size distribution of flocs was studied as a function of kaolinite concentration in the range 1-3 mg/l at 20 min flocculation time in case of alum and polyelectrolyte. The results are presented graphically by three-dimensional and contour plots showing the floc number as a function of coagulant dose and flocculation time. The results are also plotted to show the required turbidity as a function of velocity gradient and flocculation time at optimum coagulant dose to locate the overall optimum working conditions. It is found from various experimental results that floc size or floc formation and growth are the principal criteria that effect the flocculation process.