Floc Fractal Dimension Research Articles

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

Interactions between turbulence, suspended sediment concentration (SSC), settling velocity, effective density, fractal dimension, and floc size were studied on the tide-dominated, muddy coastal shelf of the southwestern Yellow Sea, China. The measurements were carried out in July 2013 at two sites located in water depths of 21.2 and 22.1 m. Negative correlations were observed between shear rate, SSC, effective density, and mean floc size, which supports the results of previous numerical, experimental, and field studies. A significant positive correlation was observed between near-bed SSC and shear rate, an indication that SSC variations are controlled by turbulence and re-suspension. In addition, significant linear relationships were found between settling velocity and other parameters (floc size, turbulence, SSC, effective density, and fractal dimension) at the two sites, indicating that the controlling factors on settling velocity are spatially variable. Principal component analysis was applied to determine the relative importance of turbulence, flocculation ability, and SSC as controls on floc size in situ. The relative contributions of turbulence, flocculation ability, and SSC to floc size (at both sites) were ~33.0%, 30.3%, and 29.7%, respectively, this being a new field-based quantitative analysis of the controls on floc size. The findings demonstrate that, in nature, flocculation ability affects floc size to the same degree as turbulence and SSC. Therefore, predictions of floc size in coastal marine environments require constraints not only on turbulence and SSC, but also on flocculation ability.

Fractal Models for Floc Density, Sedimentation Velocity, and Floc Volume Fraction for High Peclet Number Reactors

Abstract Analytical models of floc characteristics are developed as components of a comprehensive flocculation model. The models are derived for reactors with a high ratio of advective fluid transport relative to diffusion (i.e., high Peclet number) and batch reactors where the floc size distribution is expected to be relatively narrow compared with completely mixed flow reactors. High Peclet number flows are obtained in gravity-driven hydraulic flocculators without mechanical agitation. Hydraulic flocculators are an ideal technology for a low carbon footprint and where robust, low maintenance operation is required. The models, combined with measurements of floc sedimentation velocity and floc volume fraction, suggest that the fractal dimension of flocs is approximately 2.3 and that 0.65–1 μm is approximately the particle size beyond which fractal geometry is needed for description of floc properties.

Coagulation performance and floc characteristics of aluminum sulfate with cationic polyamidine as coagulant aid for kaolin-humic acid treatment

Abstract In this study, novel cationic polyamidine (Pa) was synthesized and used as coagulant aid with aluminum sulfate (AS) for kaolin-humic acid simulated water treatment. The effects of Pa on coagulation performance and floc properties were investigated. Results showed that Pa addition significantly enhanced the removal of turbidity, ultraviolet absorbance at 254 nm wavelength (UV 254 ) and dissolved organic carbon (DOC). AS–Pa exhibited high coagulation efficiency at border pH range and increased floc size and growth rate significantly. Floc recovery ability was also improved, while floc fractal dimension was lower with Pa addition. This would be attributed to high cationic charge density and long chain of Pa, which could enhance the effect of charge neutralization and adsorption bridging.

Influence of flocs breakage process on membrane fouling in coagulation/ultrafiltration process—Effect of additional coagulant of poly-aluminum chloride and polyacrylamide

The additional coagulant dosing strategy was applied in a coagulation–ultrafiltration (UF) process for treatment of drinking water. When poly-aluminum chloride (PACl) dose was set as the optimal coagulant dosage (alum 0.15mM), the additional PACl and polyacrylamide (PAM) were added after breakage to further examine their benefits and impact on membrane fouling. The average size of flocs re-formed with additional non-ionic PAM was larger than that of additional PACl. The fractal dimension of flocs (dpf) was proved to play an important role on membrane fouling. Broken flocs re-formed with additional non-ionic PAM has more convoluted boundaries and lower effective density than the one with additional PACl, which is available to form loose and porosity cake layer on surface of membrane. Microscopic observations of membrane surface demonstrated that there was obvious correlation between the structure of cake layer and the fractal dimension of flocs. Besides, reversible fouling (RF) and irreversible fouling (IF) were also investigated in our study. The additional PACl dosing could lower membrane fouling, but irreversible fouling did not reduce because much more positive charged of flocs may adsorb on the surface of membrane under electrostatic attraction. As for non-ionic PAM, both of RF and IF were simultaneously decreased. As a result, the structural characteristics and surface electrical of flocs are two main mechanisms caused irreversible fouling.

Effect of using polydimethyldiallylammonium chloride as coagulation aid on polytitanium salt coagulation performance, floc properties and sludge reuse

Polytitanium salt has attracted more and more attention recently, yet there is not much research on combining polytitanium salt with polymer flocculant. This study focused on the application of polydimethyldiallylammonium chloride (PDMDAAC) as coagulant aid with polytitanium sulfate (PTS) in fulvic acid (FA) water treatment. Effect of dosing sequence (PTS dosed first donated as PTS+PDMDAAC; PDMDAAC dosed first donated as PDMDAAC+PTS), dose and solution pH was investigated. Coagulation sludge of dual-coagulants was also reused to produce TiO2. Results showed that compared with use of PTS alone, turbidity and FA removal were both enhanced by dual-coagulants. In addition, this study revealed that floc size and floc growth rate of PTS+PDMDAAC were also significantly improved and floc strength and recovery ability were also increased by PTS+PDMDAAC. AS for PDMDAAC+PTS, floc size, growth rate, strength and recovery ability were similar to those of PTS. Floc fractal dimension of these three coagulants was in an order of PDMDAAC+PTS>PTS>PTS+PDMDAAC. Furthermore, TiO2 produced by dual-coagulants sludge showed higher photocatalytic activity than that produced by PTS sludge.

Effects of different coagulants on flocculation performance and floc properties in northwest China raw water treatment

The water of northwest China, characterized by low turbidity, low temperature, and micro-pollution, has posed difficult problems for water treatment plants. This study deployed a pilot-scale grid flocculation system to treat melt water from the Qinghai-Tibet Plateau in northwest China. A range of traditional coagulants were used on the low temperature, low turbidity, and micro-polluted melt water, to investigate the effect of coagulant types on flocculation performance and floc properties. Flocculation performance varied, depending upon the coagulant used. Turbidity and organic matter were removed with the greatest efficiency by polyaluminum chloride (PAC), followed by polyaluminum ferric chloride, followed by aluminum sulfate (alum). At a PAC dosage of 25 mg/L, the settled water's residual turbidity was lower than 1 NTU, meeting the Chinese national water-quality standard. Floc fractal dimensions of the three coagulants initially decreased, and then increased as the flocculation process yielded larger particles. This suggested that low turbidity could significantly affect the floc fractal dimension. Studying floc size distribution indicated that floc size in the grid flocculation tank was relatively uniform; the floc size distribution of PAC was the narrowest. The results could be used to inform operations of the Xining water treatment plant.

Fractal structure and permeability of membrane cake layers: Effect of coagulation–flocculation and settling as pretreatment steps

Effect of pretreatment on the flux performance of ultrafiltration membranes is studied and interpreted in terms of structural characteristics of suspended flocs and membrane cakes formed from these flocs. Coagulation–flocculation with different values of G‾tmix and optional pre-settling are applied to approximate pretreatment conditions of inline, direct, and conventional filtration processes. A new method for experimentally determining fractal dimension of membrane cakes, Dcake, based on permeate flux data and Happel permeability model is proposed and employed to show that Dcake correlates with the fractal dimension of flocs, Dfloc. The broad range of Dfloc values (1.95<Dfloc<2.56) is found to map onto a narrow range of Dcake values (2.92<Dcake<2.99) indicating breakup and restructuring that flocs undergo as they are incorporated into a growing cake. Information on the structure of flocs and membrane cakes complements flux data and may be useful in optimizing feed pretreatment in terms of the tradeoff between the mass of the cake, its permeability and responsiveness to hydraulic and chemical cleaning.

Pre-coagulation on the submerged membrane fouling in nano-scale: Effect of sedimentation process

Abstract Pre-coagulation and then flocculation with/without sedimentation before ultrafiltration (CSUF/CUF) was compared to explore the process for treating synthetic humic rich water and controlling membrane fouling. The sedimentation process caused larger flocs to be removed and zeta potential of the remaining flocs to be more negative. Also the fractal dimension of flocs became smaller after sedimentation process. All the data seemed to suggest that sedimentation process can improve the membrane fouling. On the contrary, the development of trans-membrane pressure (TMP) in CSUF surprisingly increased higher than that in CUF. The scanning electron microscope (SEM) images of cake layer on the surface of membrane showed that the size of nano-scale primary particles formed in coagulation process was heterogeneous. It also showed that the flocs formed by larger nano-scale primary particles were removed by sedimentation process, and the smaller nano-scale primary particles in CSUF maybe the crucial reason causing higher development of TMP. The density of cake layer on the CUF membrane surface with larger nano-scale particles was much lower than that by CSUF. Therefore, the characteristic of flocs, especially the size of nano-scale primary particles, may be the main factor inducing higher increase of TMP in CSUF, which should be explored in the future.

Effect of Activated Sludge Retention Time, Operating Temperature, and Influent Phosphorus Deficiency on Floc Physicochemical Characteristics and UV Disinfection

Pilot-scale sequencing batch reactors (SBRs) were used to assess the effects of sludge retention time, temperature, and influent phosphorus level on floc physicochemical characteristics, effluent quality, and UV disinfection kinetics. Increasing the operating temperature from 12 to 22 °C caused an increase in the activated sludge flocs fractal dimension from 0.1 to 0.2, and improved the UV disinfection of final effluent. Influent phosphorus limitation, i.e., COD:N:P of 100:10:0.3, caused the formation of more spherical flocs with higher resistance to UV disinfection (by 1 log). However, influent phosphorus starvation, i.e., COD:N:P of 100:10:0.03, decreased the average floc size and sphericity, increased the final effluent turbidity, and lowered effluent UV dose demand. The findings provide useful information in terms of modifying wastewater treatment processes in the context of water reuse and improving UV disinfection efficiency.

Settling velocities of multifractal flocs formed in chemical coagulation process

A number of different flocculation mechanisms are involved in the formation of chemical coagulation flocs. Consequently, two flocs with the same size may have been formed by different mechanisms of aggregation and therefore have different arrangement of primary particles. As a result, two flocs with the same size may have different masses or mass distributions and therefore, different settling velocities. Although the correct estimation of the floc mass and density is critical for the development of the floc settling model, none of the suggested floc settling models incorporate the information on mass distribution and variable density of flocs. A probability-based method is used to determine the floc fractal dimensions on floc images. The results demonstrated that flocs formed in lime softening coagulation are multifractal. The multifractal spectra indicated the existence of a multiple fractal dimensions as opposed to the unique box-counting dimension which is a morphology-based fractal dimensions typically introduced into the Stokes' Law. These fractal dimensions may provide information on the flocs' aggregation mechanism, floc's structure, and the distribution of mass inside the floc. More research is required to investigate how to utilize the information obtained from the multifractal spectra to incorporate the variable floc density and nonhomogeneous mass distribution of flocs into the floc settling models.

점착성 퇴적물의 염분과 퇴적물농도에 따른 플럭 특성: 플럭카메라를 이용한 실험연구

To examine floc characteristics of cohesive bed sediment of the Yeongsan River estuary, a floc camera system has been developed and utilized to observe flocs under varying conditions. In order to validate the floc camera system, sand particles were passed through 88-125 and 63-88 μm sieves and observed within the laboratory. Mean grain size and settling velocities were found to be 102 and 56.2 μm and 6.7 and 5.9 mm/s, respectively. Artifacts of particles estimated outside of the sieve range are attributed to being imaged out of the depth of focus. However, as mean grain size and settling velocity of each size class were within the confidence interval, the floc camera system was confidently used to examine cohesive bed sediments of Yeongsan River estuary. The bed sediment sample was prepared with a concentration of 0.1 g/L in 0 psu deionized water. The mean grain size, settling velocity and fractal dimension of flocs were 40.6±0.66 μm, 14 mm/s, and 2.86, respectively. Experiments were also conducted using different salinities (10 and 34 psu) and sediment concentrations (0.1 and 0.3 g/L). Despite changing these parameters, the mean observed grain size and settling velocities were found to be the same within the error range of the system. The relatively higher values of settling velocity and fractal dimension are considered a result of the sediment containing relatively small concentrations of organic matter. Moreover, consistent floc size over various grain sizes and concentrations may be the result of insufficient turbulence to aggregate flocs.

Effect of hydraulic conditions on flocculation performances and floc characteristics in Chinese herbal extracts by chitosan and chitosan hydrochloride

Chitosan and chitosan hydrochloride was used in the flocculation of impurities in Chinese herbals extract of Xiao’er Kechuanling Oral Liquid (XKOL) to study the effect of different fast-mixing hydraulic conditions on the flocculation performance and floc characteristics. The results showed that with the increase of fast-mixing speed chitosan floc size increased initially and then decreased, while chitosan hydrochloride floc size declined. The trends of the strength and recovery factors were contrary to that of the floc size for both flocculants. Floc fractal dimensions of both chitosan and chitosan hydrochloride increased firstly and declined latterly in response to increasing fast-stirring intensity. Fast-mixing speed had greater influence on chitosan hydrochloride flocs size than that of chitosan. Chitosan hydrochloride flocs had bigger size, higher strength and recoverability compared with chitosan flocs. In addition, compared with traditional alcohol precipitation of XKOL, both chitosan and chitosan hydrochloride presented better flocculation efficiency with high clarity, impurities removal, and retention rate of active ingredient chlorogenic acid. The lowest turbidity 14.9 NTU and 10.4 NTU was achieved at fast-stirring speed 1.31m/s and 1.05m/s by chitosan and chitosan hydrochloride, respectively. The removal rate of tannin and protein by chitosan hydrochloride reached to the highest value of 78.9% and 49.3% at about 1.05m/s, respectively, which were higher than that of chitosan at optimum 1.31m/s. The retention rate of chlorogenic acid was slightly influenced by the fast-mixing rate with above 93% in the studied speed range.

Study on Energy Consumption Distribution of High Ferric-Based Silicon Coagulant Using Fractal Dimension

High ferric-based silicon coagulant is a kind of new self-made coagulant. The high ferric content was introduced in the preparation process of the coagulant, and the effect was good in dealing with simulated industrial wastewater with lead. The beaker test indicated that the lead removal rate reached the highest 96.48% when the rapid stirring speed was 300r/min and stirring time was 1min, low stirring speed was 80r/min and stirring time was 15min, the dosage of the coagulant was 3.5ml/L. And the fractal dimension of flocs was 1.67674 under that optimum conditions. The low stirring stage was divided into three different stages in the orthogonal experiment of energy consumption, and the result showed that the optimum combination of flocculation was: velocity gradient G1=67.7s-1, stirring time T1=4min; G2=57.8 s-1, T2=5min; G3=23.9s-1, T3=6min. The removal rate of lead ion improved and the energy consumption decreased when the flocculation was divided into different stages. The relations between fractal dimension and energy consumption distribution can be obtained by calculated the fractal dimension of different stages. The stirring speed can be controlled and the flocs can be prevented from being broken by observing the flocs.

Analyzing the Distribution of Energy Consumption of Coagulation Technological Using the Fractal Dimension

Using self-made high-ferric-based silicon coagulant to deal with the lead containing industrial wastewater. Firstly we can define the optimum dosage of coagulant by jar test, and then utilize orthogonal experiment to seek the best energy consumption allocation decision at different levels. Combining with the fractal dimension of flocs, it can directly reflect the flocs growth of each stage in the distribution of energy consumption, and can guide the operating conditions of coagulation technology. This method not only makes water treatment economical and efficient, but also offers the comparatively scientific design data for the design of the flocculation tank in water works.

Predicting the settling velocity of flocs formed in water treatment using multiple fractal dimensions

Here we introduce a distribution of floc fractal dimensions as opposed to a single fractal dimension value into the floc settling velocity model developed in earlier studies. The distribution of fractal dimensions for a single floc size was assumed to cover a range from 1.9 to 3.0. This range was selected based on the theoretically determined fractal dimensions for diffusion-limited and cluster–cluster aggregation. These two aggregation mechanisms are involved in the formation of the lime softening flocs analyzed in this study. Fractal dimensions were generated under the assumption that a floc can have any value of normally distributed fractal dimensions ranging from 1.9–3.0. A range of settling velocities for a single floc size was calculated based on the distribution of fractal dimensions. The assumption of multiple fractal dimensions for a single floc size resulted in a non-unique relationship between the floc size and the floc settling velocity, i.e., several different settling velocities were calculated for one floc size. The settling velocities calculated according to the model ranged from 0 to 10 mm/s (average 2.22 mm/s) for the majority of flocs in the size range of 1–250 μm (average 125 μm). The experimentally measured settling velocities of flocs ranged from 0.1 to 7.1 mm/s (average 2.37 mm/s) for the flocs with equivalent diameters from 10 μm to 260 μm (average 124 μm). Experimentally determined floc settling velocities were predicted well by the floc settling model incorporating distributions of floc fractal dimensions calculated based on the knowledge of the mechanisms of aggregation, i.e., cluster–cluster aggregation and diffusion-limited aggregation.

Anionic polymer compound bioflocculant as a coagulant aid with aluminum sulfate and titanium tetrachloride

The objectives of this study are to investigate the impacts of anionic polymer compound bioflocculant (CBF) as a coagulant aid on coagulation performance and floc characteristics with titanium tetrachloride (TiCl4) and aluminum sulfate (Al2(SO4)3). The effect of dosing sequence was also investigated. Floc size, breakage, regrowth and floc fractal dimension were examined using a laser diffraction instrument. The results showed that CBF with TiCl4 or Al2(SO4)3 coagulants exhibited synergistic effects by promoting dissolved organic carbon (DOC) removal. For both TiCl4 and Al2(SO4)3, the floc recoverability was improved by CBF addition, and the flocs formed by TiCl4 and the corresponding dual-coagulants showed weaker recovery ability than those by Al2(SO4)3 and the corresponding dual-coagulants. Fractal dimension analysis demonstrated that the floc fractal dimension values increased with the increasing coagulant dose. The effect of CBF on fractal dimension of the flocs generated by TiCl4 was different from that of Al2(SO4)3.

Influence of flocs breakage process on submerged ultrafiltration membrane fouling

In order to explore the influence of floc characteristics on membrane fouling, flocs after breakage and re-growth were compared with those formed by conventional coagulation process when alum was used as coagulant. The results showed that, though the average size of flocs after breakage and re-growth was smaller than that without breakage, the fractal dimension of flocs after breakage and re-growth was lower than that without breakage independent of the dosage of alum. The increase of trans-membrane pressure (TMP) was lower when the flocs formed in breakage and re-growth process. When the dosage of alum increased, the fractal dimension ( D 2) of flocs without breakage decreased a little while D 2 of flocs with breakage and re-growth was nearly the same. Moreover, lower dosage of alum (0.1 mM) caused higher increase of TMP with conventional coagulation process, comparing with higher dosage of alum (0.3 mM); while it was nearly the same when the flocs formed with breakage and re-growth process. The fractal dimension is an important factor influencing the increase of TMP compared with the average size of flocs, and a lower frequency of small flocs may cause a smaller increase of TMP. The characteristics of flocs surface changed after breakage and re-growth and this may also affect the increase of TMP.

Application of lead flocs fractal dimension by new poly-ferric-silicon coagulant

Poly-ferric-silicon, made by the fly ash extract, is well in dealing with the lead industrial wastewater. Meanwhile combed with the application of fractal theory in coagulation, the test is conducted the jar test in different dosages and pH value, and found that the fractal dimension of flocs and the lead removal after precipitation can be showed a good correlation, so this is achieved the online monitoring the coagulation effect by flocs fractal dimension. Additionally, in order to assure the optimal hydraulic condition of the new type poly-ferric-silicon coagulant, the test is utilized orthogonal experiment to seek the best hydraulic energy consumption allocation scheme which is G1 = 67.7 s–1, t = 3 min, G2 = 57.8 s–1, t = 5 min, G3 = 23.9 s–1, t = 7 min by dividing the stirring intensity (G value) and stirring time (t value) into different three gears in flocculation stage. and got the appropriate flocs fractal dimension being 1.48, 1.66 and 1.80 in each stage of the distribution of energy consumption. So combing the energy consumption allocation scheme with fractal dimension, it not only be effectively illustrated the rational of the energy consumption allocation decision, but also offered the comparatively scientific design data for designing of the flocculation tank, being made the water treatment economical and efficient.

Study of Flocs Morphology of Chitosan Coagulation Aid Treatment and Fractal Dimensions

Flocculation water treatment is one of the important aspects of water treatment .The aim of this work is to use PFS for treating Yellow River surface water and different molecular weights of chitosan as coagulant aid. Electron microscope was used to observe flocs morphology and study CTS coagulation aid morphological change, floc image with microscope camera system analysis, calculation of floc fractal dimension. The results show that the different molecular weights of CTS in dealing with surface raw water to play a good coagulation aid effect. Microscope and image analysis system of flocs morphology show that fractal dimension of morphology of PFS / CTS were significantly higher ,Among them，high molecular weight of CTS as coagulant aid，and fractal dimension of morphology of PFS/ CTS were 1.1026,1.5593 , low molecular weight of CTS as coagulant aid，and fractal dimension of morphology of PFS/ CTS were 1.0904,1.5440 respectively. Floc fractal dimension changes to better reflect the flocculation level and treatment effect for the establishment of floc fractal dimension number of changes in the coagulation control is provided for reference.

Effect of pH on humic acid removal performance in coagulation–ultrafiltration process and the subsequent effects on chlorine decay

The effect of pH on coagulation performance and floc characteristics with respect to the treatment of humic acid (HA) solution using polyferric chloride (PFC) as coagulant was investigated in this study. Ultrafiltration was used after coagulation to further remove organics under three pH conditions. The subsequent effects on chlorine decay were studied using a first decay model and AQUASIM modeling software. The results indicated that PFC had different coagulation mechanisms in different pH regions. Charge neutralization was the dominant mechanism in acidic region, while sweep was the predominant mechanism at pH >6.0. HA was effectively removed in acidic region and turbidity removal efficiency was higher in neutral and alkaline regions. The median equivalent volumetric diameter ( d 50) of flocs formed in coagulation process in acidic region was larger than that of flocs formed at pH 9.0. The flocs formed at pH 5.0 were more compact because larger floc fractal dimension ( D f ) was observed. Floc breakage behavior showed that flocs formed at different pH values gave different floc strength and recovery ability, and the strength and recovery factors of the flocs varied in the following order: pH 5.0 >4.0 >9.0. The treated water at pH 5.0 possibly contained the minimal amount of disinfection by-products (DBPs) precursors due to the minimal reacting compounds present in the treated water. DBPs precursors were probably prone to be removed by coagulation process during which flocs with larger strength factor, recovery factor and D f were formed.