Search

Abstract: Flow interactions with aquatic vegetation and effects on sediment transport and nutrient redistribution are uncertain in shallow aquatic ecosystems. Here we quantified sediment transport in the Everglades by progressively increasing flow velocity in a field flume constructed around undisturbed bed sediment and emergent macrophytes. Suspended sediment <100μm was dominant in the lower range of laminar flow and was supplied by detachment from epiphyton. Sediment flux increased by a factor of four and coarse flocculent sediment >100μm became dominant at higher velocity steps after a threshold shear stress for bed floc entrainment was exceeded. Shedding of vortices that had formed downstream of plant stems also occurred on that velocity step which promoted additional sediment detachment from epiphyton. Modeling determined that the potentially entrainable sediment reservoir, 46gm−2, was similar to the reservoir of epiphyton (66gm−2) but smaller than the reservoir of flocculent bed sediment (330gm−2). All suspended sediment was enriched in phosphorus (by approximately twenty times) compared with bulk sediment on the bed surface and on plant stems, indicating that the most easily entrainable sediment is also the most nutrient rich (and likely the most biologically active). [Copyright &y& Elsevier]

To conduct the micro-environment study of flocs in an enhanced biological phosphorus removal (EBPR) process, a phosphate ion-selective microelectrode was developed. The cobalt-based microelectrodes have tip diameters of 5–20μm and respond to all the three forms of phosphate ions, namely, H2PO4 −, HPO4 2−, and PO4 3−. The calibration curve at pH 7.5 had a slope of 31.5mV per decade change of concentration and a R 2 value of 0.99. Other characteristics of this microelectrode, such as response time, interferences from pH, ion strength, DO and other anions were also evaluated. [Copyright &y& Elsevier]

Abstract: This paper introduces a new method to estimate in-situ floc density and porosity of three particle-size classes: 0.45–10, 10–63 and, 63–250μm. LISST-100 and CatNet (a novel on-board filtration system of nested filters) were used to measure suspended particle volume and mass concentrations of 32 and 3 size-classes, respectively. Two field experiments were conducted in 2004 and 2006 in the head region of Gaoping Submarine Canyon (GPSC) to test this method. In each experiment CTD and LISST-100 profiling and simultaneous water sampling were carried out on board R/V Ocean Research III. In 2004, the water samples were filtered in the laboratory after the cruise using traditional methods. CatNet was used in 2006 and the seawater filtration was done on board. Assuming the observed suspended particles were all flocs composed of primary particles (with assumed density of 2.65g/cm3) and interstitial water (with assumed density of 1.025g/cm3) we estimated the volume of primary particles. The volume difference between flocs (measured from LISST-100) and primary particles is the interstitial pore space in flocs. Subsequently, the porosity of a floc particle is the ratio of the volume of the interstitial pore space to that of the floc particle. Results for 2004 show erroneous values of estimated floc porosities, which do not appear in 2006. The major difference is that the seawater was filtered immediately on board using CatNet in 2006. After removing erroneous data related to after-cruise filtering, the averaged floc porosity and density in the three grain-size classes were 47.0, 64.0, 85.9% and 1.89, 1.61, 1.25g/cm3, respectively. There is a trend that larger particles have lower density, which is supported by literature. The temporal variations of floc density and porosity of all three particle-size groups were larger in the surface than near the bottom of the submarine canyon. This vertical variability resulted from flocculation and biogenic processes in the surface of the coastal ocean, and the terrestrial source of the Gaoping River. Floc density is an important physical parameter to evaluate the settling flux of suspended sediments in estuarine and marine environments. This approach provides direct in-situ floc bulk densities of different grain-size classes, which has advantages over conventional methods. [Copyright &y& Elsevier]

Coagulation control plays a significant role in the final yield of sludge volume during water and wastewater treatment. The precise control of coagulant dosage, floc formation and aggregation behaviour becomes the important target for the coagulation process both in water and wastewater treatment. A critical review is presented first in this paper on the recent advances in coagulation control. In particular, the development of an in-situ image detecting system (IDS) based on characterization of floc properties, involving average diameter, fractal dimension and apparent strength is discussed. The results show that the data obtained from the IDS are generally in accordance with the outcome of common coagulation experiment, and have sensitivity for the slow stirring rate, raw water turbidity and coagulant dosage, in different degrees. The combination of IDS and ANN model is also discussed. This provides a possibility for applying the proposed IDS to control the coagulation process in water and wastewater treatment. [ABSTRACT FROM AUTHOR]

Theory is developed to represent the macroscopic features of a floc blanket held in steady state. Flocs are treated as non-porous entities possessing a fractal structure. A particular feature of the analysis is the recognition of floc strength, floc sizes adjusting to the prevailing rate of energy dissipation within the blanket. Account is taken of the floc size distribution, with expressions derived to describe the blanket settling velocity and mass flux. Analysis of experimental data yielded detail of the blanket floc size scale (dvo), water content and strength. The mass flux was maximised when the floc volume fraction was close to 0.17. It was shown that the upflow velocity (u) complied with the dependence u ∝o=Md5-Dmax in which dmax is a maximum floc size, M the blanket solids concentration, D the fractal dimension and So a strength scaling factor. Consideration was given to blanket characteristics in non-stationary conditions. The final section of the paper focuses on the attenuation capacity. It was argued that dvo should be as low as practicable in order to promote the capture of feed flocs by interception, to reduce the water content of the solids waste stream when using hydrolysing coagulants, and may also enhance the mass flux. [ABSTRACT FROM AUTHOR]

The paper focuses on the properties of flocs that are required to service the needs of solid-liquid separation in conventional treatment units. Beyond the basic requirements of minimum size and surface nature to enable effective trapping on a collecting surface, field data indicate that floc water content affects treatability (as gauged by the hydraulic loading rate or treatment rate). Floc blanket clarifiers, DAF and filter units are examined in terms of implications of floc size, density and strength, insofar as they interact with the process dynamics. It is shown that these features come into play both individually and collectively and are sensitive to the floc fractal structure. It is argued that floc strength often plays a critical role in separation processes through its impact on floc size. Recognising the benefits of densification, the paper provides specific advice on how densification can be achieved. Among the many options considered, it is noted that the most straightforward means of securing greater density or strength, is by use of smaller flocs, this also benefiting dewaterability. [ABSTRACT FROM AUTHOR]

As a pretreatment for membrane microfiltration (MF), the use of powdered activated carbon (PAC) with a particle size much smaller than that of conventional PAC (super-powdered PAC, or S-PAC) has been proposed to enhance the removal of dissolved substances. In this paper, another advantage of S-PAC as a pretreatment for MF is described: the use of S-PAC attenuates trans-membrane pressure increases during the filtration operation. The floc particles that formed during coagulation preceded by S-PAC pretreatment were larger and more porous than the floc particles formed during coagulation preceded by PAC pretreatment and those formed during coagulation without pretreatment. This result was due to increased particle–particle collision frequency and better removal of natural organic matter, which inhibits coagulation by consuming coagulant, before the coagulation reaction. The caked fouling layer that built up on the membrane surface was thus more permeable with S-PAC than with normal PAC. Both physically reversible and irreversible membrane foulings were reduced, and more stable filtration was accomplished with S-PAC pretreatment. [Copyright &y& Elsevier]

Abstract: The hydrodynamic diameter (D h) of cationic polyacrylamides (c-PAM) in water can either decrease or increase dramatically in the presence of small amounts of β-cyclodextrin (β-CD). It is proposed that the CD partially disperses the charge on the polymer thereby promoting associations within or among neighboring polymer strands. Turbidity measurements show that β-CD enhances the c-PAM induced flocculation of wood pulp fibers, which is in keeping with previous observations on sludge dewatering. The CD-polymer combinations that are the most effective for fiber flocculation are also those for which D h of the polymer is reduced the most. In situations where the CD compacts the c-PAM, the fiber network associated with the c-PAM is also compacted giving rise to a tighter floc. [Copyright &y& Elsevier]

The principal aim of this study is to analyze a seawater coagulation process by means of the evaluation of flocculation index and fractal dimension of flocs. Floc size was evaluated by flocculation index (FI) and floc shape by fractal dimension. Two coagulation parameters of the coagulant type and the mixing condition were selected to evaluate a seawater coagulation process. The study results indicate that the coagulant type was important for seawater coagulation. The coagulant type affected the kinetics of floc formation, floc size and floc shape. Floc formed fast at use of ferric chloride, while it formed slowly at use of aluminum salts. Ferric chloride and titanium chloride produced bigger flocs than aluminum salts. Flocs formed by use of ferric chloride and titanium chloride were more spherical than Al floc. Fe floc was more insensitive to a change in the coagulant dose and the seawater pH than Al floc. Slow mixing was more important for seawater coagulation than rapid mixing. Tapered flocculation produced bigger flocs than constant flocculation. Increase in slow mixing speed from 20 rpm to 40 rpm resulted in formation of bigger flocs, which was reflected by lower settled turbidity value. On the base of the study results, it can be stated that the evaluation of floc characteristics could be a useful tool in order to optimize the seawater coagulation process. [ABSTRACT FROM AUTHOR]

Abstract: This paper discussed the coagulation characteristics of BPA with polyaluminum chloride (PACl-Al13) as coagulant, examined the impact of coagulation pH, PACl-Al13 dosage, TOC (total organic carbon) and turbidity on BPA removal, and analyzed the possible dominant mechanisms in water coagulation process. Formation and performance of flocs during coagulation processes were monitored using photometric dispersion analyzer (PDA). When the concentration of humic acid matters and turbidity was low in the solution, the experimental results showed that the removal of BPA experienced increase and subsequently decrease with the PACl-Al13 dosage increasing. The optimal PACl-Al13 dosage was found at BPA/PACl-Al13 =1:2.6(M/M) under our experiment conditions. Results show that the maximum BPA removal efficiency occurred at pH 9.0 due to the adsorption by Al13 aggregates onto BPA rather than charge neutralization mechanism by polynuclear aluminous salts in the solution. The humic acid matters and kaolin in the solution have significant effect on BPA removal with PACl-Al13 in the coagulation. The BPA removal will be weakened at high humic matters. The removal rate of BPA increased and subsequently decreased with the turbidity increasing. [Copyright &y& Elsevier]

The marine photosynthetic bacterium Rhodovulum sulfidophilum produces extracellular nucleic acids involved in its flocculation. Previously, we showed that the RNA fraction of these extracellular nucleic acids released into the culture medium contains mainly non-aminoacylated fully mature-sized tRNAs and fragments of 16S and 23S rRNAs. Here, we report the characterization of extracellular DNA itself and its production during cultivation. No differences were detected in nucleotide sequence between the intracellular DNA and extracellular soluble DNA on Southern blotting. Whole intracellular DNA seemed to be released from the cell. The bacterial floc was degraded by deoxyribonuclease or ribonuclease treatment, indicating that at least the extracellular DNA and RNAs in the floc are involved in the maintenance of the floc. When cultivated in nutritionally rich medium, the bacteria formed small flocs and produced large amounts of extracellular DNA, which were solubilized in the medium. In nutritionally poor medium, however, huge flocs of cells appeared and almost no extracellular soluble DNA was observed in the medium. As the floc was degraded by deoxyribonuclease treatment, it seems likely that the extracellular soluble DNA observed in the rich medium may be incorporated into the large floc and play a role in floc maintenance in poor medium. Addition of an inhibitor of quorum sensing, α-cyclodextrin, inhibited huge floc maintenance in the nutritionally poor medium. In the presence of α-cyclodextrin, the floc was rapidly degraded and extracellular soluble DNA production increased. [ABSTRACT FROM AUTHOR]

Abstract: A new formulation for floc yield strength of cohesive sediment is theoretically derived and incorporated into a flocculation model based on variable fractal dimension. The new flocculation model is validated with existing data on the temporal evolution of floc size measured in the laboratory. Comparing with existing flocculation models using a constant yield strength, it is found that new flocculation model based on variable yield strength and variable fractal dimension is superior in predicting the temporal evolution of floc size. It is also demonstrated that the present model results are very similar to that using an empirical formulation of variable yield strength suggested by Sonntag and Russel (1987. Structure and breakup of floccs subjected to fluid stressses. II. Theory. J. Colloid Interface Sci. 115(2), 378–389) when the empirical coefficient is specified according to our theoretical value. Hence, it is concluded that the new variable yield strength formulation derived in this study and the variable fractal dimension are effective in improving the prediction of flocculation process. [Copyright &y& Elsevier]

The dimension of the separation zone in the dissolved air flotation (DAF) process is practically determined by the rise velocity of the bubble-floc agglomerates: flocs attached to several bubbles. To improve the flotation velocity and particle removal efficiency in the DAF process, many researchers have tried to attach as many bubbles as possible to flocs. In this study, the rise velocity of bubble-floc agglomerates, considered to be the most important factor in designing the separation zone of the flotation tank in the DAF process, was investigated on the basis of comparison between theoretical and observed results. The observed rise velocity measured by a particle image analyser (PIA) and the predicted value, however, did not show similarity, in contrast to what we had expected. Furthermore, the simulated results using population balance to predict the maximum number of attached bubbles on a floc were too impractical to accept under the practical condition of the surface of the floc if there was no change of bubble size. These findings led us to suggest that there were three possible causes which could conceivably explain the observations. It was suggested that the differences between predicted and observed values could be attributed to one or more of the possible causes. [ABSTRACT FROM AUTHOR]

Although flocculation has been widely applied to improve filtration performance before filtered dry stack tailings storage, it is still a challenge to create flocculated aggregates having desired characteristics which are both conducive to improving the filtration rate and reducing the filter cake moisture content. In this paper, the alternate shear conditions were investigated to enhance flocculant-aided filtration performance of coal tailings. The focused beam reflectance measurement (FBRM) was used as an in-situ monitor to measure the floc size under different shear conditions in the presence of anionic polyacrylamide. Compared with single shear conditions, sequenced flocculation produced stronger flocs. It was also found that the flocs formed under two cycles of high (1192.8 s−1) and low (637.6 s−1) shear rates were the strongest and contained fewer particles and small flocs. The particle vision measurement (PVM) was used to analyze the effects of alternate shear conditions on floc morphological characteristics. It was observed that the floc structure became more compact with the number of cycles. Lastly, the filtration experiments were conducted to determine the filtration performance of coal tailings. The results showed that the coal tailings had the best comprehensive filtration performance under the sequenced flocculation with two cycles of high and low shear rates, the filtration time was 12.17 min, which was very close to the fastest 12.03 min of single low shear rate, and 21.2% of cake moisture content was about the same as the minimum 21.1%. The filtration outcomes were consistent with that given by FBRM and PVM. [Display omitted] • Sequenced flocculation improved the filtration performance of coal tailings. • Alternate shear condition has a profound impact on floc compactness. • The size and shape characteristics of flocs were monitored in situ. [ABSTRACT FROM AUTHOR]

Over 2,000 flocs were involved in the calculations of floc fractal dimensions and floc shape factors to examine the effects of low temperature on floc structures. The 3-D fractal dimension of flocs was found to decrease from 2.48 at 22°C to 2.24 at 2°C, indicating flocs are more compact at the higher temperature. At 22°C, floc fractal dimensions were not significantly affected by flocculation time. However, at the low temperature, 2°C, fractal dimensions were found to increase with flocculation time, indicating that flocs generated at low temperature need more time to be well formed. On the other hand, low temperature did not exert significant influence on floc shape factors. Statistical analyses show that the examined shape factors of the flocs, roundness R and smoothness S, followed probability rules. Around 80% of flocs have an R value ranging from 0.5 to 0.8, and about 75% of flocs have an S value in the same range. The mechanism of floc growth during coagulation of kaolinite suspensions is reaction-limited clustercluster aggregation (RLCA). [ABSTRACT FROM AUTHOR]

The complexity of natural water made it difficult to remove fluoride. Based on the environmental problems found in the investigation, the fluoride removal research in the water containing algal cells was carried out. In this study, AlCl 3 and [AlO 4 Al 12 (OH) 24 (H 2 O) 12 ]7+ (Al 13) were used to remove fluoride. Additionally, the role of aluminum speciation in fluoride removal and the effect of Microcystis aeruginosa on the fluoride removal by different aluminum species coagulants were elucidated. The results showed that AlCl 3 mainly removed fluoride by physical interactions, surface adsorption and enmeshment. When algal cells were added to the system, the fluoride removal rate increased from 22.75 % to 72.99 % at a dosage of 40.0 mg/L. This was because algal cells greatly increased the distribution of Al(OH) 3 in the flocs. In particular, the specific surface area of the flocs containing algal cells reached 160.77 m2/g, which allowed more fluoride to be adsorbed. However, excessive Al3+ led to serious damage to algal cells and release of intracellular organic matter (IOM), worsening the effect of defluoridation. F− and Al3+ formed AlF2+ and AlF 2 + via complexation in water. These compounds were not conducive to defluoridation. Al 13 removed fluorine mainly through ion exchange, substitution and hydrogen bonding. Algal cells had an inhibitory effect on defluorination, which was observed in the process of coagulation by different Al dosages. Al 13 achieved agglomeration of algal cells and generated small and dense flocs through charge neutralization and electrostatic patch mechanism. Once Al 13 combined with algal cells and algae organic matter (AOM), the reaction between Al 13 and fluoride would be weakened. Al 13 not only maintained the defluoridation performance, but also did not damage the integrity of algal cells, even at high dosages. [Display omitted] • Defluorination by AlCl 3 relied merely on physical actions. • Algal cells promoted the adsorption of F− by changing the distribution of Al(OH) 3. • Algal cells increased F− removal rate by 50.24 % at 40.0 mg/L AlCl 3. • Al 13 removed F− mainly through ion exchange, substitution and hydrogen bonding. • The presence of algal cells impaired the ability of Al 13 to remove F−. [ABSTRACT FROM AUTHOR]

Better understanding of sediment flocculation will better help to predict fine sediment transport. Multiple advanced instruments were employed to get the field observations in the turbidity maximum of the Changjiang Estuary. Floc pictures were taken by a scanning electron microscope in the laboratory. The sediment flocculation dynamics and the floc characteristics are investigated in this paper. The results show that the morphology and size of flocs show obvious tidal variations. There are diverse flocs in each tidal cycle, mainly including loose, porous and dense flocs, which are mainly comprised of silt and clay. They have indistinct or distinct shapes, rough or less rough surfaces, incompact or compact structures. The floc size is highly related to the tidal processes. The average floc size (94.8 μm) during water slacks is larger than that (24.1 μm) during maximum floods and ebbs, owing to the lower flow velocity during water slacks. The average floc size (105.6 μm) during high water slacks is larger than that (83.9 μm) during low water slacks due to the higher salinity during high water slacks. The average floc size (74.7 μm) during neap tide is larger than that (44.3 μm) during spring tide, which can be attributed to the lower flow velocity, the higher salinity and the finer primary particle during neap tides. Additionally, the floc size increases gradually from the surface to the bottom. The turbulent shear stress is the controlling factor for sediment flocculation. The maximum flocs can be formed under the condition of mid-low flow velocity and the optimal flow velocities for the maximum flocs during neap and spring tides are 0.41 and 0.56 m/s, respectively. The floc size decreases significantly with the increase of turbulent shear when the turbulent shear rate parameters during neap and spring tides are higher than about 3 and 4 s−1, respectively. The conclusions can help to extend our understanding of flocculation dynamics and help to predict the fine sediment transport. • Floc properties are observed in the turbidity maximum of the Changjiang Estuary. • There are diverse flocs, mainly including loose, porous and dense flocs. • Sediment flocculation shows obvious tidal variations over a tidal cycle. • The floc size decreases significantly with the increase of turbulent shear. [ABSTRACT FROM AUTHOR]

Transport of particulate organic material can impact watershed sediment and nutrient budgets and can alter the geomorphologic evolution of shallow aquatic environments. Prediction of organic aggregate ('floc') transport in these environments requires knowledge of how hydraulics and biota affect the entrainment, settling, and aggregation of particles. This study evaluated the aggregation and field transport dynamics of organic floc from a low-gradient floodplain wetland with flow-parallel ridges and sloughs in the Florida Everglades. Floc dynamics were evaluated in a rotating annular flume and in situ in the field. Under present managed conditions in the Everglades, floc is not entrained by mean flows but is suspended via biological production in the water column and bioturbation. Aggregation was a significant process affecting Everglades floc at high flume flow velocities (7.0 cm s−1) and during recovery from high flow; disaggregation was not significant for the tested flows. During moderate flows when floc dynamics are hydrodynamically controlled, it is possible to model floc transport using a single 'operative floc diameter' that accurately predicts fluxes downstream and to the bed. In contrast, during high flows and recovery from high flows, aggregation dynamics should be simulated. When entrained by flow in open-water sloughs, Everglades floc will be transported downstream in multiple deposition and reentrainment events but will undergo net settling when transported onto ridges of emergent vegetation. We hypothesize that net transport of material from open to vegetated areas during high flows is critical for forming and maintaining distinctive topographic patterning in the Everglades and other low-gradient floodplains. [ABSTRACT FROM AUTHOR]

The morphology, entrainment, and settling of suspended aggregates ('floc') significantly impact fluxes of organic carbon, nutrients, and contaminants in aquatic environments. However, transport properties of highly organic floc remain poorly understood. In this study detrital floc was collected in the Florida Everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment experiments. Although Everglades flocs are similar to other organic aggregates in terms of morphology and settling rates, they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands. Flume experiments documented that Everglades floc was entrained at a low bed shear stress of 1.0 × 10−2 Pa, which is considerably smaller than the typical entrainment threshold of mineral floc. Because of similarities between Everglades floc and other organic floc populations, floc transport characteristics in the Everglades typify the behavior of floc in other organic-rich shallow-water environments. Highly organic floc is more mobile than less organic floc, but because bed shear stresses in wetlands are commonly near the entrainment threshold, wetland floc dynamics are often transport-limited rather than supply limited. Organic floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes, which has implications for ecosystem metabolism, materials cycling, and even landscape evolution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Natural energy was successfully used to power a water treatment system. • Solar-powered electrocoagulation produced large flocs at a low current density. • The gravity-driven membrane bioreactor achieved a high flux of 25 L/m2h. • Large flocs and membrane rejection facilitated the enrichment of useful microbes. • Nitrogen was largely removed by Nitrospira and Diaphorobacter bacteria. Rural water treatment is generally more challenging than urban water treatment. This study proposed a novel rural water treatment system effectively harnessing solar energy and gravitational hydropower. Influent was initially fed to a solar-driven electrocoagulation unit, in which UV 254 level was reduced (by almost 60%) and large flocs (averaging up to 66.2 μm in diameter) were formed. The effluent was then introduced to a gravity-driven ceramic membrane bioreactor (GDCMBR) at different water head differences (ΔH = 0.5 or 1.0 m). Generally, applying the greater water head difference (ΔH = 1.0 m) did not enhance removal of turbidity and organic matter, but it led to a reasonably high flux (25.9 L/m2/h). The GDCMBR enriched various useful microorganisms such as nitrifiers (Nitrospira bacteria), and denitrifiers (Diaphorobacter bacteria), enabling almost complete elimination of NH 3 -N and NO 2 –-N. Overall, the findings of this study suggest the possibility of sustainable operation during rural water treatment. [ABSTRACT FROM AUTHOR]

Fluorescence in situ hybridization (FISH) provides a unique tool to study micro-organisms associated with particles and flocs. FISH enables visual examination of micro-organisms while they are structurally intact and associated with particles. However, application of FISH to wastewater and sludge samples presents a specific set of problems. Wastewater samples generate high background fluorescence due to their organic and inorganic content making it difficult to differentiate a probe-conferred signal from naturally fluorescing particles with reasonable certainty. Furthermore, some of the FISH steps involve harsh treatment of samples, and are likely to disrupt the floc structure. This study developed a FISH protocol for studying micro-organisms that are associated with particles and flocs. The results indicate that choice of a proper fluorochrome and labeling technique is a key step in reducing the background fluorescence and non-specific binding, and increasing the intensity of the probe signal. Compared to other fluorochromes tested, CY3 worked very well and enabled the observation of particles and debris in red and probe signal from microbes in yellow. Fixation, hybridization, and washing steps disturbed the floc structure and particle-microbe association. Modifications to these steps were necessary, and were achieved by replacing centrifugation with filtration and employment of nylon filters. Microscope slides generated excellent quality images, but polycarbonate membrane filters performed better in preserving the floc structure. [ABSTRACT FROM AUTHOR]

Naturally occurring aggregates are considered of fractal or fractal-of-fractals interior structure. Recent studies utilizing dye staining and confocal laser scanning microscopy (CLSM) techniques have revealed the extremely complex, interconnected pore networks for floc interior. Detailed structural analysis on the real floc architecture is determined for building up a comprehensive floc model. This work interprets structural characteristics of flocs using multifractal analysis. A direct method by Chhabra and Jensen properly evaluated the singularity strength and singularity spectrum on architectures of two artificial fractal systems. However, direct evaluation of multifractal characteristics of wastewater flocs has limitations, alternatively acquiring analytical results to be misleading. Particularly, the singularity spectrum presents excessively large values in the limit as q → +∞ and exhibits very large error bars in the limit as q → -∞. This is attributable to the uneven distribution of mass in flocs and insufficient spatial resolutions provided by CLSM techniques. The flaws in applying multifractal analysis on naturally occurring objects are discussed. [ABSTRACT FROM AUTHOR]

Abstract: In this study, coagulation of kaolinite suspensions at low temperatures is compared with that at an ambient temperature of 22°C, and the process is examined with regard to the coagulation rate (CR) and chemical aspects of coagulation. Experiments using a photometric dispersion analyzer (PDA) show that coagulation of kaolinite suspensions can be taken as a two-phase process. Low temperature greatly reduces the CR of the first phase but not that of the second one. On the other hand, results show that low temperature did not serve to impede the hydrolysis of aluminum [Al(III)] within 1min of alum addition. The measurements of electrophoretic mobility (EM) indicate that destabilization of kaolinite particles by hydrolyzed Al species was not hindered by low temperature within 1min of alum addition. Slow coagulation at low temperature is due to the lowered CR but not the altered chemistry aspect of Al(III). Furthermore, the change in settled turbidity after 20-min flocculation as a function of coagulant dosage was more severe in the cold because of the low CR. Elongating floc-growth time, as observed, was able to counterbalance the retarded CR at low temperature and improve turbidity removal efficiency. [Copyright &y& Elsevier]

The application of floc fractal dimension has been investigated in this work to determine if this parameter can have operational significance in water treatment. Natural organic matter suspensions were coagulated with aluminium sulphate and varying concentrations of a non-ionic polymer. The fractal dimensions of the flocs formed were measured using light scattering and settling combined with image analysis. By using the correct methodology, optimum floc properties could be determined using the floc fractal dimension combined with the floc size and strength data. [ABSTRACT FROM AUTHOR]

This study evaluated the beneficial effects on the coagulation process of combining coagulants with Fe and Al in the removal of turbidity and DOC (dissolved organic carbon), and proposed conditions for proper operation of a coagulation process. In addition, the floc characteristics and sludge dewater ability were evaluated. Blended coagulants were more effective than single coagulants at lower concentrations in water purification. The optimal blended ratio for the removal of DOC was 1.45 mM as Al/mM as Fe. Also, blended coagulants were less affected than single coagulants by pH, temperature, and rapid mixing intensity. Based on the results of the change in the apparent molecular weight distribution (AMWD) of DOC in raw and treated water by coagulation, low molecular weight organic matters were removed by 40.7% for the blended coagulant (1.45 mM as Al/mM as Fe). Blended coagulants formed larger flocs than single coagulants did. At pH 6.0, floc strength and sludge dewaterablity were both improved. [ABSTRACT FROM AUTHOR]

Abstract: The flocculation of paper fibers by cationic polyacrylamides (c-PAM) was studied by imaging the fibers that remain free during flocculation. Studies with fibers of different lengths showed that the degree of flocculation increases with fiber length, with the best flocs being formed with mixtures of short and long fibers. Short fibers did not flocculate by themselves but were captured by flocs formed with longer fibers. The short fibers strengthen the floc and give it shear resistance. Shear had the expected effect of promoting flocculation at low Reynolds number but disrupting it at higher values. For a given polymer the maximum floc size for a mixture of fibers is dictated by the length distribution of the fibers. The polymer dose governs the rate of flocculation. The technique is especially useful in following the tail end of the flocculation process. At this stage a floc is almost fully grown and a small increase in its size would be very difficult to measure by conventional techniques. In contrast, the number of free fibers measured by single fiber imaging decreases rapidly at this point. [Copyright &y& Elsevier]

The combined use of nanoparticle and polyelectrolyte as retention aids in pulp and paper industry tend to give better flocculation (retention) and drainage (dewatering) than conventional polyelectrolyte flocculation. The combined use of alumina nanoparticle and polyelectrolyte in conditioning waste activated sludge was investigated in the current study. Alumina with three different sizes (139.5, 241.7, and 326.4 nm) was utilized in combination with a cationic polyelectrolyte (T3052) of molecular weight of 1.1 x 107 and charge density of 2.1meq/g. It was found from capillary suction time (CST) and specific resistance to filtration (SRF) measurement that sludge conditioned with alumina/polyelectrolyte showed a better dewaterability than polyelectrolyte alone. In addition, it was found that the better dewaterability was obtained as alumina became smaller. Floc size and fractal dimension of flocs were examined as well. The mechanism of enhanced dewaterability was proposed that alumina nanoparticles became adsorbed onto sludge and positive patches were formed. The electrostatic repulsion made the polyelectrolyte more stretched, and resulted in more effective flocculation and bridging as polyelectrolyte was added. Dosing sequence also affected the conditioning effectiveness. However, the combined use of silica nanoparticles and a cationic polelectrolyte, KP-201C, or alumina nanoparticles and an anionic polyelectrolyte, AP410, did not result in improved dewaterability of waste activated sludge. Possible explanation was discussed. Preliminary results show that some in-depth work is needed regarding the introduction of nanoparticles in sludge conditioning. [ABSTRACT FROM AUTHOR]

Abstract: Direct movie analysis of the Brownian motion of single colloidal particles under optical microscope was carried out to determine hydrodynamic diameter. Mean squared displacements of individual particle against time interval of observation were obtained from the trace of Brownian motion. The hydrodynamic diameter is obtained via diffusion coefficient determined on the basis of Einstein relation. The validity of the applied method was statistically confirmed by the comparison of predicted relative error with those obtained from the measurement using uniform polystyrene latex particles of three different diameters. Determination of hydrodynamic diameters with coefficients of variation (CV) less than 6% was achieved when processing 501 frames. Achieved coefficients of variation correspond to those statistically predicted for the Brownian motion. Obtained diameter of doublet was consisted with those reported by other researchers. In the case of flocs composed with primary particle more than three, the value of CV slightly increases up to 7.3%. This increment can be ascribed to deviation of center of mass determined from projected image from true value. However, within this accuracy the hydrodynamic diameters of coagulated flocs being composed of up to six primary particles were determined. The determined hydrodynamic diameters were found to be significantly smaller than the maximum distances in the projection indicating different power law relation against the number of composing particles in flocs. [Copyright &y& Elsevier]

High gradient magnetic separation (HGMS) for purification of wastewater from paper factory has been developed and withstand for 1 year operation. The system developed is a high gradient magnetic separation (HGMS) system with superconducting magnet which purifies wastewater continuously from a paper mill. The magnetic field generated by the superconducting magnet for HGMS is 2 T at the center of the bore, operating current 100 A, 680 mm long and 400 mm bore NbTi solenoid. The developed system which treats wastewater of 2000 t/day has been confirmed to show the expected performance. The purpose of the developed system is to separate COD constituents from the wastewater efficiently and economically in a small space. The required performances are follows, i) the set-up area is less than 6 m × 6 m, ii) COD of the treated water is less than 100 ppm and water can be recycled, and iii) a system can treat wastewater more than 2000 t/day. The design and the performance of the system are reported. [ABSTRACT FROM AUTHOR]

Column and pilot scale experiments for a chemical treatment involving the use of coagulants to remediate heavy metal contaminated groundwater were performed. Granulated lime (Ca(OH)2) and calcium carbonate (CaCO3) were used as coagulants and contaminated groundwater obtained at an abandoned Fe-mine in Korea was used for the experiments. The main removal mechanism of heavy metals in the experiments was “sweep precipitation” by coagulation. Using granulated lime as a coagulant in the column experiment, more than 98% of As and Ni were removed from artificially contaminated water. When granulated calcium carbonate was used in the artificially contaminated water, the removal efficiencies of Ni and Zn were more than 97%, but As removal efficiency was lower than 50%. For the continuous column experiment with mixed lime and calcium carbonate at a 1:1 (v/v) ratio, almost all As was removed and more than 98 % of Ni was removed. For pilot scale experiments (acryl tank: 34cm in length and 24cm in diameter), the removal efficiencies of As and Cd were above 96% for 150l groundwater treatment and their accumulated removal capacities linearly maintained. This suggests that coagulants could treat more than 22 times greater groundwater volume compared with the volume of coagulants used. [Copyright &y& Elsevier]

Abstract: Ultrasonication is an energy intensive process used to enhance organics’ solubilisation and used in promoting methane yield from wastewater sludge. Applying limited ultrasound without full disruption of floc structure or cell walls can significantly enhance methane yield from sludge at reduced energy cost. This work probed the spatial distribution of extracellular polymeric substances, cells in the original wastewater flocs, and the yielded fragments following weak ultrasonication using a process of multiple staining and a confocal laser scanning microscope technique. The stereological information of the three-dimensional architecture of the original wastewater floc and ultrasonicated fragments was extracted and compared. The local structural changes following weak ultrasonication were presented for the first time, which should also correlate with the enhanced methanogenesis thereby produced. [Copyright &y& Elsevier]

Abstract: The present effort is the development of a multiscale modeling, simulation methodology for investigating complex phenomena arising from flowing fiber suspensions. Specific consideration was given to dynamic simulations of viscoelastic fibers in which the fluid flow is predicted by a method that is a hybrid between Direct Numerical Simulations (DNS) and Large Eddy Simulation techniques (LES), and fluid fibrous structure interactions (FSI) will be taken into account. Numerical results are presented for which focus is on fiber floc deformation by hydrodynamic forces in turbulent flows. Dynamics of simple fiber networks in a shearing flow of water in a channel flow illustrate that the shear-induced bending of the fiber network is enhanced near the walls. Fiber–fiber interaction in straight ducts is also investigated and results show that deformations would be expected during the collision when the surfaces of flocs will be at contact. Smaller velocity magnitudes of the separated fibers compare to the velocity before collision implies the occurrence of an inelastic collision. In addition because of separation of vortices interference flows around two flocs become very complicated. The results opening the possibility for developing a meaningful numerical model of the fiber flow at the continuum level where an Eulerian multi-phase flow model can be developed for industrial use. [Copyright &y& Elsevier]

Abstract: Flocs generated by various coagulation mechanisms exhibit different size, strength and structure. The properties and fractal dimensions of flocs formed under three common coagulation mechanisms, i.e. charge neutralization, sweep and bridging, were investigated at various hydraulic conditions. The results showed that the floc size decreased with the increasing average velocity gradient G and the stable floc size exponent γ was of the following hierarchy: charge neutralization (0.6107)>sweep (0.5618)>bridging (0.3674). Furthermore, fractal dimensions of flocs were the highest when formed by sweep and the lowest when generated by bridging flocculation. The mass fractal dimensions measured by light scattering were between 2.0 and 3.0 and the floc strength was between 0.01 and 0.58 N m−2. An intrinsic unity of the relationship among floc size, fractal dimensions, floc strength under the three coagulation mechanisms was demonstrated. [Copyright &y& Elsevier]

Abstract: Freeze/thaw treatment is an effective sludge-dewatering technique. The efficiency of dewatering of freeze/thawed sludge declines as the approaching ice front engulfs flocs at a high freezing rate. The forces exerted on a wastewater-sludge floc by the approaching ice front and the surrounding fluid field determine whether the ice front engulfs the floc. Two wastewater flocs of sizes 2170 and were hung on a cantilevered beam which underwent constant-speed freezing (5 or ). Beam deflection and the shape of sludge floc were recorded to estimate the force exerted by the ice and the elasticity of the sludge flocs. The force exerted by an approaching ice front on the floc ranged from 1.6 to , and was attributable primarily to the interaction between the gas bubbles formed between the floc and the ice front. When the ice had partly engulfed the floc, the corresponding force continuously increased as freezing continued, compressing the unfrozen part of the floc and pulling apart the network of the frozen part of the floc. The change in floc shape was tracked to estimate the interior elasticity of , and the elongation coefficient of for the flocs herein. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: The focused beam reflectance measurement (FBRM) probe was directly inserted into a small fermentor with a working volume of 650mL and the on-line monitoring technique for the size distribution of SPSC01, a self-flocculating yeast strain, was established. It was found that the floc size distribution could be characterized by its mode, M, which was further correlated by a power function with the stirring speed, r. Therefore, the designated floc size distributions were obtained through controlling the stirring speed. The batch fermentation times were significantly extended when the same levels of ethanol and biomass concentrations were reached, but the floc size distributions characterized by M increased from 100 to 600μm. These experimental results indicated that the intra-particle mass transfer limitation existed for such a self-flocculating yeast ethanol fermentation system and the kinetics ought to be categorized into two different levels: intrinsic and observed. The impacts of the floc size distributions on the observed rates for glucose uptake and ethanol production were quantitatively investigated by manipulating the stirring speed so that the designated floc size distributions were achieved. The effectiveness factors, η S and η P for glucose uptake and ethanol production, respectively, were further evaluated. It was found that both the floc size distribution and the level of limiting substrate concentration affected η S and η P. [Copyright &y& Elsevier]

Abstract: This study examined shape changes in two typical wastewater flocs subjected to cyclic freezing and thawing and the associated force exerted by the ice front. While freezing, the engulfing ice front gradually pulled the floc apart. Subsequent thawing only partially restored the floc''s shape. By the Maxwell model, used to interpret gross shape deformations, both flocs were visco-elastic objects exhibiting time-varying rheological characteristics which were more viscous than elastic. Detailed observations of floc 1 deformation demonstrated a two-stage force–displacement relationship. Following 1 cycle of freezing and thawing, the interior structure of the floc deteriorated and the force required to elongating a unit length of floc decreased by 60%. The original floc 2 had a dense “core” and loose “tail”; the core was more resistant to deformation under normal stress than the loose tail. Although both flocs had similar shapes and sizes and were acquired from the same activated sludge stream at a wastewater treatment plant, their rheological behaviors differed substantially. A comprehensive theoretical model for freezing and thawing processes should incorporate these rheological characteristics as they corresponded to observed structural changes and reduction in bound water content in sludge following a cyclic treatment of freezing and thawing. [Copyright &y& Elsevier]

The use of predictive models for the understanding and management of sediment and contaminant transport generally requires knowledge of particle size and settling velocity. Particle size is often obtained by direct measurements, and the settling velocities are usually predicted using the Stokes' law (or a modification thereof) for single-grained spherical particles. Such measurements and estimates are not satisfactory measures for cohesive sediments, which exist as agglomerated particles called flocs and whose behaviour is significantly different from that of the single-grained particles. Direct measurement of settling velocity and size using optical methods in settling columns has also been employed to improve these predictions; however, the subjectivity in determining which particles are in focus results in unreliable size data. An out-of-focus particle will generally possess a larger size than in reality. This paper evaluates a laser-assisted particle sizing/settling velocity determination technique's ability to eliminate the subjectivity and improve particle-sizing accuracy during settling column experiments. Although the diffraction of light by the translucent standard beads (used for evaluating the technique's accuracy for determining particle size) posed a problem, the results suggest that this technique has potential for assisting researchers to obtain the most accurate settling particle size data possible. [ABSTRACT FROM AUTHOR]

The effect of shear on the formation and break-up of flocs generated using cationic, anionic and non-ionic polymers, and dual combinations of these, has been investigated using conventional jar test procedure and by continuous optical monitoring. The breakage of flocs was followed at a high stirring speed, corresponding to average shear rate (G) of approximately 520 s-1. Most of the breakage occurred within a few seconds of increasing the shear rate. After each breakage, the stirring rate was reduced to the original value of 50 rpm (G ≈ 23 s-1) to allow the flocs to regrow. For cationic-anionic polymers case, the regrowth of flocs was fully reversible and the breakage factors were smallest indicating highest floc strength. In contrast, flocs formed using non-ionic polymer together with anionic or cationic did not produce as strong flocs. It is found that the sequence of polymer addition is not very significant for floc formation and reformation when the cationic-anionic dual system is used. [ABSTRACT FROM AUTHOR]

Immersed membrane systems, and those with in-line coagulation, have been extensively applied in drinking water systems. Sedimentation is usually replaced by membrane processes in both systems. In these systems, voluminous flocculent aggregates formed during coagulation could be potential foulants. When raw waters with high turbidity are introduced, particle loadings to membrane due to coagulation pretreatment are enormous and thus could increase fouling. In general, during the rainy season, the turbidity of the Han River water, which supplies drinking water for the City of Seoul, Korea, is more than a hundred times higher than usual. Therefore, effects of floc on membrane fouling were investigated with highly turbid waters. Two turbidity concentrations, 40 and 200 NTU, were formulated by the addition of kaolin (used as a natural particle surrogate) to the Han River raw water. The results showed that the flux decline behaviours of the highly turbid waters were different from those of natural raw water. Coagulation pretreatment was very effective at reducing membrane fouling. Flocculent aggregates showed a negative effect on the flux decline, but a positive effect on the membrane cleaning efficiency. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with the preparation of concentrated calcium carbonate suspensions at 72wt% by filtration–compression in presence of chemical dispersants. A quantitative analysis of the disaggregating of filter cakes under shear into concentrated suspensions is proposed. Two rheological models were used: an Herschel–Bulkley model to relate the relative viscosity to the shear rate, a modified Krieger and Dougherty model to relate the relative viscosity to the solid concentration at given shear rate. The maximum packing fraction of particles in the cakes was estimated as well as the ratio between the aggregates and the particle size r f/r p. This ratio logically declines with the intensity of shear. It shows that an advanced cake disaggregating was obtained for low shear rates of 10s−1. Two processes of filtration–compression were also compared: a filtration of deflocculated suspension (FDS) and an innovative precoat filtration of deflocculated suspension (PFDS). The results showed that PFDS improved the cake dryness and specific resistance as well as the flowability of the final concentrated suspension. [Copyright &y& Elsevier]

Abstract: The fate of active proteins in environmental matrices such as wastewater sludge, soil, and organic amendments is not well understood . In the present paper, we report the use of green fluorescent protein (GFP) as a probe protein to investigate the behaviour of proteins in wastewater sludge. We developed a procedure to quantitatively detect the active form of this protein in such a matrix. The procedure is based on the fluorimetric analysis of GFP in the separated liquid and solid fractions of sludge. We then tested the suitability of the approach by monitoring GFP added to aerobic and anaerobic sludge. Under aerobic conditions at 20°C, most GFP immediately associated with the sludge solid fraction. About 20% of the fluorescence due to solid fraction associated GFP was still present after 72h, which suggests a relative persistence of proteins in this system. Under anaerobic conditions at 35°C, fluorescence signal due to GFP was reduced by 90% after only 6h. [Copyright &y& Elsevier]

Abstract: Under typical operating conditions, the microbial fraction of activated sludge flocs is approximately 40% by weight. The objective of this research is to evaluate the feasibility of using ultrasonic irradiation to disrupt activated sludge flocs allowing for the subsequent separation of active and inactive fractions. If separation of floc components is possible, then methods may be incorporated into wastewater treatment plant operations whereby only the inactive fraction of floc is wasted (i.e., of waste activated sludge, WAS), which in turn could increase the overall effective biological solids retention time, leading to increased process robustness with no net increase in reactor size. The results indicate that ultrasonic irradiation of WAS at 800Wl−1 followed by 30min of settling can produce a supernatant with heterotrophic specific oxygen uptake rates (SOURs) of over two times the SOUR measured in the bulk mixed liquor. Under these conditions 26% of the initial heterotrophic activity was recovered within only 11% of the initial volatile mass. Similarly, autotrophic analysis revealed that nitrifying organisms, while sensitive to the effects of ultrasonic irradiation, can be separated from the activated sludge floc and recovered. An irradiation density of 200Wl−1 with an exposure time between 1 and 2min produced a supernatant with a specific ammonia removal rate of over two times the initial mixed liquor rate. [Copyright &y& Elsevier]

Abstract: Floc size has substantial impact on sludge dewaterability, which might be increased or reduced after freezing and thawing. It is commonly assumed that floc size would be increased by low-speed freezing, with a planar ice front rejecting most flocs ahead of it to form large aggregates. We demonstrate in this work that an advancing planar ice front can not only engulf an activated sludge floc of size 3030 μm, but also fragment it. During floc freezing, when the ice engulfed a thin layer of floc, the latter would be pulled apart vertically by the action of the former. This particular portion of floc was then axially elongated and fixed in the frozen layer, with accumulated force pushing upward. In the present test the floc''s vertical length was increased by over 92% and its width decreased by 37% over freezing. The force measurement and floc morphology tracking revealed that the force gradient that pulled apart the floc was 0.0027 N/m. The floc under investigation was fragmented at the point where the normal stress acting on the interior network exceeded 8 Pa. [Copyright &y& Elsevier]

Abstract: The effect of natural organic material (NOM) and turbidity on the powdered activated carbon (PAC) adsorption of the odour compound 2-methylisoborneol (MIB) was evaluated during alum coagulation. The character of the flocs, in terms of their size and fractal dimensions (D f), was used to interpret the observed adsorption behaviour of MIB during the coagulation process. As the alum dose was increased, the adsorption of MIB decreased. This was determined to be due to the size of the flocs, with larger flocs incorporating PAC into their structure, reducing the efficiency of mixing, and the bulk diffusion kinetics for the MIB molecule. The presence of turbidity also reduced MIB adsorption due to the formation of larger flocs. The character of NOM was found to have a greater influence on the adsorption of MIB than the floc structure. [Copyright &y& Elsevier]

Abstract: The main focus of the paper is to review current understanding of floc structure and strength. This has been done by reviewing current theoretical understanding of floc growth and breakage and an analysis of different techniques used for measuring floc strength. An overview has also been made of the general trends seen in floc strength analysis. The rate of floc formation is a balance between breakage and aggregation with flocs eventually reaching a steady-state size for a given shear rate. The steady-state floc size for a particular shear rate can, therefore, be a good indicator of floc strength. This has resulted in the development of a range of techniques to measure floc size at different applied shear levels using a combination of one or more of the following tools: light scattering and transmission; microscopy; photography; video and image analysis software. Floc strength may be simply quantified using the initial floc size for a given shear rate and the floc strength factor. More complex techniques have used theoretical modelling to determine whether flocs break by large-scale fragmentation or smaller-scale surface erosion effects, although this interpretation is open to debate. Impeller-based mixing, ultrasound and vibrating columns have all been used to provide a uniform, accurate and controllable dissipation of energy onto a floc suspension to determine floc strength. Other more recent techniques have used sensitive micromanipulators to measure the force required to break or compress individual flocs, although these techniques have been limited to the measurement of only a few hundred flocs. General trends emerge showing that smaller flocs tend to have greater strength than larger flocs, whilst the use of polymer seems to give increased strength to only some types of floc. Finally, a comparison of the strength of different types of floc (activated sludge flocs, organic matter flocs, sweep flocs and charge neutralised flocs) has been made highlighting differences in relative floc strength. [Copyright &y& Elsevier]

Abstract: Focussed beam reflectance measurement is a technique that shows some promise as a technique for the online characterisation of floc size and structure. A scanning laser is focused into process fluid and the reflected intensity is measured as a function of time. This light intensity signal is normally processed to return chord length measurements which contain combined information on particle size and shape. This study shows that the unprocessed signal can be expected to encode information about the texture of the particle being scanned in addition to size and shape. For the purpose of characterising floc structure, a power law exponent can be recovered from the Fourier transform of the unprocessed signal and this in turn is related to the mass fractal dimension of flocs. The technique is demonstrated with computer generated flocs and with flocculated polystyrene latex of a primary particle size of 5μm and a mass fractal dimension of D m =2.5 as determined by the volume obscuration method. Results obtained through simulation studies into scanning of computer generated flocs demonstrate that a correlation exists between the power law exponent and the mass fractal dimension. Loose structures with mass fractal dimension of D m =1.64 returned a power law exponent of β =−l.77 whilst a tighter structure of mass fractal dimension of D m =2.34 returned a power law exponent of β =−1.92. Results obtained through scanning of polystyrene latex flocs of mass fractal dimension of D m =2.49 returned a power law exponent of β =−2.00 which appears not to be in quantitative agreement with the simulation results. [Copyright &y& Elsevier]