On the variability of near-bed floc size due to complex interactions between turbulence, SSC, settling velocity, effective density and the fractal dimension of flocs

2016 ◽  
Vol 36 (2) ◽  
pp. 135-149 ◽  
Author(s):  
Yang Yang ◽  
Ya Ping Wang ◽  
Chunyan Li ◽  
Shu Gao ◽  
Benwei Shi ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Settling Velocity ◽  
Effective Density ◽  
Floc Size ◽  
Complex Interactions

scholarly journals Characterisation of floc size, effective density and sedimentation under various flocculation mechanisms

2020 ◽  
Vol 82 (7) ◽  
pp. 1261-1271
Author(s):  
Yuping Fan ◽  
Xiaomin Ma ◽  
Xianshu Dong ◽  
Zeyu Feng ◽  
Yingdi Dong
Keyword(s):  
Settling Velocity ◽  
Structural Characteristics ◽  
Effective Density ◽  
Floc Size ◽  
Floc Structure ◽  
Trivalent Cations ◽  
Coal Tailings ◽  
Better Than ◽  
Flocculation Mechanisms

Abstract Floc structure plays an important role in the separation of coal wastewater. In this study, a camera-based method is used to evaluate quantitatively the structural characteristics of flocs generated by different coagulants and flocculants. The correlations between particle size, settlement velocity and effective density of coal tailings flocs are analysed. The results show that the statistical settling velocity increases linearly with floc size, while the effective density decreases with increase in floc size. Different flocculation mechanisms lead to diverse growth abilities of flocs. When the flocculant is used alone, the quality of the flocs generated by the flocculants, cationic polyacrylamide (CPAM) and non-ionic polyacrylamide (NPAM), is better than that generated by anionic polyacrylamide (APAM). However, the combination of trivalent cations and APAM yields a much better effect than that obtained using CPAM and NPAM. Flocs become larger and more compact when treated with a coagulant combined with a flocculant.

scholarly journals Flocculation of Clay Suspensions by Anionic and Cationic Polyelectrolytes: A Systematic Analysis

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 999
Author(s):  
Ahmad Shakeel ◽  
Zeinab Safar ◽  
Maria Ibanez ◽  
Leon van Paassen ◽  
Claire Chassagne
Keyword(s):  
Light Scattering ◽  
Shear Rate ◽  
Settling Velocity ◽  
Rheological Analysis ◽  
Floc Size ◽  
Clay Concentration ◽  
History Of ◽  
Settling Column ◽  
Cationic Polyelectrolytes ◽  
Shear History

The characteristics of clayey suspensions, majorly composed of quartz microparticles, in the presence of anionic and cationic polyelectrolytes were investigated using different techniques. A wide range of clay concentrations was used, i.e., from 0.07 to 1000 g/L for different experimental techniques, based on the fact that the clay concentration possible to analyze with selected experimental methods was significantly different. The optimum flocculant to clay ratio was defined as the ratio that gives the fastest initial floc growth by static light scattering or fastest initial settling velocity by settling column experiments. In case of anionic polyelectrolyte, it was observed that the optimum flocculant dose depends on the amount of cations present in the system. For suspensions made with demi-water, a lower optimum flocculant dose (<1 mg/g) than for suspensions prepared in tap water (2.28 mg/g) was observed. At these lower salinities, the supernatant remained turbid in all the experiments and was, therefore, not a good measure for optimal anionic based flocculation. The equilibrium floc size at a given shear rate was found to be independent on the shear history of the floc and only dependent on the current applied shear. This was confirmed by both light scattering and rheological analysis. In case of cationic polyelectrolyte, the optimum flocculant ratio (5–6 mg/g) corresponded to the ratio that gives the lowest electrophoretic mobility for each clay concentration and to the ratio that gives the fastest settling velocity for the highest clay concentrations (12–15 g/L), where static light scattering measurements were not possible. All investigation techniques, therefore, proved to be good indicators for predicting the optimum flocculant to clay ratio. For the lowest concentrations (1.75–8.7 g/L) studied by settling column measurements, the optimum flocculant ratio was observed to increase with decreasing clay concentration, for fixed mixing conditions. The optimum flocculant to clay ratio was not always corresponding to the clearest supernatant and the size of flocs at optimum dosage was dependent on the mixing efficiency. The equilibrium floc size at a given shear rate was found to be dependent on the shear history of the floc and the current applied shear. This was confirmed by both light scattering and rheological analysis.

Analysis of sludge aggregates produced during electrocoagulation of model wastewater

2015 ◽  
Vol 73 (1) ◽  
pp. 161-166
Author(s):  
B. Załęska-Chróst ◽  
R. Wardzyńska
Keyword(s):  
Wastewater Treatment ◽  
Fractal Dimension ◽  
Settling Velocity ◽  
Paper Industry ◽  
Additional Parameter ◽  
Treatment Control ◽  
Sludge Flocs ◽  
Lower Water Content ◽  
A Current ◽  
Industry Wastewater

This paper presents the results of the study of sludge aggregates produced during electrocoagulation of model wastewater of a composition corresponding to the effluents from the cellulose and paper industry. Wastewater was electrocoagulated statically using aluminium electrodes with a current density of 31.25 A m−2 and 62.50 A m−2. In subsequent stages of the treatment, sludge flocs were collected, their size was studied and their floc settling velocity (30–520 μm s−1) and fractal dimension (D) were determined. The values of D ranged from 1.53 to 1.95 and were directly proportional to the degree of wastewater treatment. Higher values of D were determined for sludge with lower water content (after 24 hours’ settling). Fractal dimension can therefore be used as an additional parameter of wastewater treatment control.

Practical design of flocculator for new polymeric inorganic coagulant - PSI

2004 ◽  
Vol 4 (1) ◽  
pp. 67-75 ◽  
Author(s):  
K. Ohno ◽  
M. Uchiyama ◽  
M. Saito ◽  
T. Kamei ◽  
Y. Magara
Keyword(s):  
Settling Velocity ◽  
Design Parameters ◽  
Mixing Process ◽  
Kaolinite Clay ◽  
Floc Size ◽  
Rapid Mixing ◽  
Water Purification System ◽  
Purification System ◽  
Practical Design ◽  
Slow Mixing

Physical characteristics of flocs formed by new polymeric inorganic coagulant, polysilicato-iron coagulant (PSI) were investigated using kaolinite clay suspended water as test water. Floc density was determined by measuring floc settling velocity and spherical equivalent floc diameter. The floc density function proposed by Tambo and Watanabe could be applied to PSI. Flocs formed by PSI showed higher floc density than those formed by alum at the same floc size. Floc size distribution after the rapid mixing as also determined. PSI could produce well-grown flocs at the stirring speed of 300 rpm. Stirring at 300 rpm for 7 minutes, residual turbidity after 15 minute sedimentation became lower than rapid mixing at 120 rpm for 5 minutes followed by slow mixing at 40 rpm for 25 minutes. Flocs formed by PSI was much stronger than those formed by alum. Using the data obtained, the design parameters of flocculator by use of PSI were estimated following Tambo and WatanabeÕs procedure. According to the estimation, it was suggested that rapid mixing process alone can make well-grown flocs and slow mixing process, which is essential for the conventional water purification system using aluminium coagulants, can be eliminated by use of PSI.

scholarly journals Tidal Variation in Cohesive Sediment Distribution and Sensitivity to Flocculation and Bed Consolidation in An Idealized, Partially Mixed Estuary

2019 ◽  
Vol 7 (10) ◽  
pp. 334 ◽  
Author(s):  
Tarpley ◽  
Harris ◽  
Friedrichs ◽  
Sherwood
Keyword(s):  
Settling Velocity ◽  
Transport Model ◽  
Tidal Flow ◽  
Sediment Concentration ◽  
Tidal Variation ◽  
Model Framework ◽  
Sediment Distribution ◽  
Floc Size ◽  
Size Classes ◽  
Suspended Floc

Particle settling velocity and erodibility are key factors that govern the transport of sediment through coastal environments including estuaries. These are difficult to parameterize in models that represent mud, whose properties can change in response to many factors, including tidally varying suspended sediment concentration (SSC) and shear stress. Using the COAWST (Coupled Ocean-Atmosphere-Wave-Sediment Transport) model framework, we implemented bed consolidation, sediment-induced stratification, and flocculation formulations within an idealized two-dimensional domain that represented the longitudinal dimension of a micro-tidal, muddy, partially mixed estuary. Within the Estuarine Turbidity Maximum (ETM), SSC and median floc diameter varied by a factor of four over the tidal cycle. Downstream of the ETM, the median floc size and SSC were several times smaller and showed less tidal variation (~20% or less). The suspended floc distributions only reached an equilibrium size as a function of SSC and shear in the ETM at peak tidal flow. In general, flocculation increased particle size, which reduced SSC by half in the ETM through increased settling velocity. Consolidation also limited SSC by reduced resuspension, which then limited floc growth through reduced SSC by half outside of the ETM. Sediment-induced stratification had negligible effects in the parameter space examined. Efforts to lessen the computation cost of the flocculation routine by reducing the number of size classes proved difficult; floc size distribution and SSC were sensitive to specification of size classes by factors of 60% and 300%, respectively.

scholarly journals Technical Note: The single particle soot photometer fails to detect PALAS soot nanoparticles

2012 ◽  
Vol 5 (4) ◽  
pp. 4905-4925 ◽  
Author(s):  
M. Gysel ◽  
M. Laborde ◽  
J. C. Corbin ◽  
A. A. Mensah ◽  
A. Keller ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Single Particle ◽  
Primary Particle ◽  
Particle Morphology ◽  
Counting Efficiency ◽  
Particle Mass ◽  
Effective Density ◽  
Soot Particles ◽  
Primary Particles ◽  
Small Primary

Abstract. The single particle soot photometer (SP2) uses laser-induced incandescence (LII) for the measurement of atmospheric black carbon (BC) particles. The BC mass concentration is obtained by combining quantitative detection of BC mass in single particles with a counting efficiency of 100% above its lower detection limit (LDL). It is commonly accepted that a particle must contain at least several tenths of femtograms BC in order to be detected by the SP2. Here we show the unexpected result that BC particles from a PALAS spark discharge soot generator remain undetected by the SP2, even if their BC mass, as independently determined with an aerosol particle mass analyser (APM), is clearly above the typical LDL of the SP2. Comparison of counting efficiency and effective density data of PALAS soot with flame generated soot (combustion aerosol standard burner, CAST), fullerene soot and carbon black particles (Cabot Regal 400R) reveals that particle morphology can affect the SP2's LDL. PALAS soot particles are fractal-like agglomerates of very small primary particles with a low fractal dimension, resulting in a very low effective density. Such loosely-packed particles behave like "the sum of individual primary particles" in the SP2's laser. Accordingly, the PALAS soot particles remain undetected as the SP2's laser intensity is insufficient to heat the primary particles to vaporisation because of their small size (primary particle diameter ~5–10 nm). It is not surprising that particle morphology can have an effect on the SP2's LDL, however, such a dramatic effect as reported here for PALAS soot was not expected. In conclusion, the SP2's LDL at a certain laser power depends on total BC mass per particle for compact particles with sufficiently high effective density. However, for fractal-like agglomerates of very small primary particles and low fractal dimension, the BC mass per primary particle determines the limit of detection, independent of the total particle mass. Consequently, care has to be taken when using the SP2 in applications dealing with loosely-packed particles that have very small primary particles as building blocks.

The effects of starvation on physical characteristics of flocs in SBR for treating saline wastewater

2007 ◽  
Vol 56 (7) ◽  
pp. 41-46 ◽  
Author(s):  
Sang-Soo Kim ◽  
Byung-Hyun Moon ◽  
Gyu-Tae Seo ◽  
Cho-Hee Yoon
Keyword(s):  
Fractal Dimension ◽  
Size Distribution ◽  
Physical Characteristics ◽  
Time Response ◽  
Saline Wastewater ◽  
Floc Size ◽  
N Removal ◽  
Removal Efficiencies ◽  
P Removal

This study focused on the effects of starvation on physical characteristics of flocs in SBR for treating saline wastewater. Feeding was stopped for 5 and 15 days. A time response of the floc to these starvation periods was monitored as well as the removal efficiencies of pollutants. Correlation between the physical characteristics of flocs and settling of sludge was conducted. As the starvation periods were increased, there was a shift in the floc size distribution from a high proportion of large flocs to the development of small size flocs. The fractal dimension of flocs also decreased, as starvation periods were increased. From the results, the effect of starvation on SBR treating saline wastewater can be ordered as follows: CODMn removal &lt; floc size and fractal dimension &lt; T-N removal &lt; T-P removal.

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