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1
Mehta, Ashish J., William H. McAnally, Farzin Samsami, and Andrew J. Manning. "REVISITING THE ROLE OF AGGREGATION IN THE SETTLING OF COHESIVE FLOCS IN THE MARINE ENVIRONMENT." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 17. http://dx.doi.org/10.9753/icce.v36.sediment.17.
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The settling velocity is the single-most important property governing the transport of cohesive flocs in the marine environment. In that regard, the instantaneously changing diameter, density and shear strength of flocs are the defining properties which distinguish floc transport from that of cohesionless particles. Thus, consideration of aggregation, which includes the dynamics of floc growth and breakup due to floc-floc collisions as well as flow-induced shearing of flocs, is a critical component of floc transport modeling.
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Zhu, Zhongfan, Dingzhi Peng, and Jie Dou. "Changes in the two-dimensional and perimeter-based fractal dimensions of kaolinite flocs during flocculation: a simple experimental study." Water Science and Technology 77, no. 4 (November 28, 2017): 861–70. http://dx.doi.org/10.2166/wst.2017.603.
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Abstract In this study, Couette flow experiments were performed to estimate the temporal evolution of the 2D and perimeter-based fractal dimension values of kaolinite flocs during flocculation. The fractal dimensions were calculated based on the projected surface area, perimeter length and length of the longest axis of the flocs as determined by sampling observation and an image-processing system. The 2D fractal dimension, which relates the longest axis length and projected surface area of flocs, was found to decrease with the flocculation time, corresponding to the production of some porous flocs from the flow shear. This fractal dimension finally reached a steady state, which resulted from a dynamic equilibrium among the floc growth, floc breakage and floc restructuring. The perimeter-based fractal dimension, which characterizes the relationship between the projected surface area and the perimeter of flocs, increases with flocculation time because the flow shear increases the collisions among the primary particles, and some irregular flocs are formed. The perimeter-based fractal dimension reaches a steady level because of the balance among floc aggregation, breakage and restructuring. In addition, a stronger turbulent flow shear makes the steady state of fractal dimensions occur early during flocculation.
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Gorczyca, Beata, and Jerzy Ganczarczyk. "Flow Rates Through Alum Coagulation and Activated Sludge Flocs." Water Quality Research Journal 37, no. 2 (May 1, 2002): 389–98. http://dx.doi.org/10.2166/wqrj.2002.025.
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Abstract The liquid velocity inside alum and activated sludge flocs was calculated using the size, settling velocity and permeability of activated sludge flocs. The permeability of activated sludge flocs has been determined experimentally. The permeability of alum coagulation flocs was assumed to be half of the permeability of activated sludge flocs based on the size of the pores in these flocs. The average flow velocity inside an activated sludge floc was calculated to be 1575 µm/s, which is in the range of the flow experimentally measured inside biofilms at a distance of about 100 µm from the substratum by Beer et al. (1995). The flow inside an alum coagulation floc was calculated to be 318 µm/s. The flow velocity inside the same flocs estimated with Davies permeability model were 0.7 µm/s for activated sludge flocs and 20 µm/s for alum coagulation flocs. Therefore, the flow velocities estimated on the basis of experimentally determined permeability were much higher than the velocities calculated with Davies permeability model. Davies permeability model assumes homogeneous distribution of porosity inside an aggregate. Direct observations made during the analysis of floc sections have proven this assumption to be wrong. Flocs have fractal structure and the models predicting their permeability should be based on this feature. Flow rates through alum and activated sludge flocs predicted on the basis of the fractal model of a floc compared well with experimental results.
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Bache, D. H., and S. H. Al-Ani. "Development of a System for Evaluating Floc Strength." Water Science and Technology 21, no. 6-7 (June 1, 1989): 529–37. http://dx.doi.org/10.2166/wst.1989.0255.
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A scheme is described as a basis for estimating floc strength by hydrodynamic shearing in a turbulent flow. Preliminary theory indicates the need to evaluate the floc size, its porosity (linked to its effective density in water) and the rate of energy dissipation in a turbulent flow (ɛ). The design and calibration of a vertical vibrating water column is described. Force transducer measurements gave estimates of (the average over the column) whereas a calorimetric technique and fluid tracer analysis provided additional information about ɛ as a function of vertical position. Flocs sedimenting through the column are subjected to increasing stress until a major rupture occurs. Preliminary experiments with clay-aluminium flocs provided insight into the factors controlling strength (σ) e.g. coagulant dose, size, and the number of primary particles within the floc (i) such that σ/i decreases with increasing floc diameter.
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Fukushi, K., N. Tambo, and Y. Matsui. "A kinetic model for dissolved air flotation in water and wastewater treatment." Water Science and Technology 31, no. 3-4 (February 1, 1995): 37–47. http://dx.doi.org/10.2166/wst.1995.0514.
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A kinetic model for DAF is presented. The author's kinetic model consists of the equations for describing a process of bubble-floc collision and attachment in a mixing zone, and a rise velocity of bubble-floc agglomerates in a flotation tank. The attachment process is formulated on a population balance model with bubbles and flocs as a flocculation in a turbulent flow. The rise velocity of bubble-floc agglomerates is formulated with size of flocs and composition of flocs including the floc density function and attached bubble number. The experimental verification was carried out, using a batch flotation tested and a mini-plant with synthetic clay suspension and colored water. The results successfully verify the validity of the model. From a given condition such as floc size and attached bubble number, the rate and extent of removal by DAF can be readily assessed by the model. A single-collector collision model, often discussed in some occasions, seems to be not useful to describe the DAF process.
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Bache, D. H., E. Rasool, D. Moffat, and F. J. McGilligan. "On the Strength and Character of Alumino-Humic Flocs." Water Science and Technology 40, no. 9 (November 1, 1999): 81–88. http://dx.doi.org/10.2166/wst.1999.0448.
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The paper describes the size, density and strength of flocs gained from a humic acid suspension coagulated with aluminium sulphate over a range of dose and pH. Flocs were generated on a continuous flow basis in an oscillatory mixer. Particle size measurements were gained using CCTV and image analysis. From this, a maximum floc size (d95) was identified. A second series of experiments examined the floc sizes of the bulk precipitate alone under equivalent conditions. It was found that the overall floc sizes of the two suspensions were broadly similar, suggesting that the floc strength was dominated by a common bonding mechanism irrespective of the presence of the humic colloids. Some features of the size distribution in response to dose and pH were attributed to the influence of surface charge. Upper floc sizes were proportional to the Kolmogorov length (η) with d95/η ∼1. For typical levels of mixing, the floc strength was estimated to be on the order of 0.1 N m−2. By analysing the breakage kinetics in energy terms and relating the strength to the density of individual floc, a physically-based structural model was developed to explain the response of the floc size to the prevailing state of mixing.
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Ren, T. T., F. Xiao, W. J. Sun, F. Y. Sun, K. M. Lam, and X. Y. Li. "Investigation of the shape change of bio-flocs and its influence on mass transport using particle image velocimetry." Water Science and Technology 69, no. 8 (February 8, 2014): 1648–52. http://dx.doi.org/10.2166/wst.2014.063.
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In this laboratory study, an advanced flow visualization technique – particle image velocimetry (PIV) – was employed to investigate the change of shape of activated sludge flocs in water and its influence on the material transport characteristics of the flocs. The continuous shape change of the bio-flocs that occurred within a very short period of time could be captured by the PIV system. The results demonstrate that the fluid turbulence caused the shift of parts of a floc from one side to the other in less than 200 ms. During the continuous shape change, the liquid within the floc was forced out of the floc, which was then refilled with the liquid from the surrounding flow. For the bio-flocs saturated with a tracer dye, it was shown that the dye could be released from the flocs at a faster rate when the flocs were swayed around in water. The experimental results indicate that frequent shape change of bio-flocs facilitates the exchange of fluid and materials between the floc interior and the surrounding water. This mass transfer mechanism can be more important than molecular diffusion and internal permeation to the function and behavior of particle aggregates, including bio-flocs, in natural waters and treatment systems.
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Jarvis, P., B. Jefferson, and S. A. Parsons. "Characterising natural organic matter flocs." Water Supply 4, no. 4 (December 1, 2004): 79–87. http://dx.doi.org/10.2166/ws.2004.0064.
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Using a dynamic optical technique and settling column apparatus, natural organic matter floc structural characteristics were monitored and evaluated over a one year period to monitor the seasonal variation in floc structure at optimum coagulation dose and pH. The results show that flocs changed seasonally with different growth rates, size, response to shear and settling rate. Autumn and summer flocs were shown to be larger and less resistant to floc breakage when compared to the other seasons, suggesting reduced floc strength. Floc strength was observed to increase with smaller median floc size. The results of the settling tests indicated that the autumnal flocs were of a more open structure which helped to explain why they settled faster. In summary, the autumnal flocs had significantly different floc characteristics although it was difficult to relate the floc structure with the incoming water characteristics.
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Tsou, G. W., R. M. Wu, P. S. Yen, D. J. Lee, and X. F. Peng. "Advective Flow and Floc Permeability." Journal of Colloid and Interface Science 250, no. 2 (June 2002): 400–408. http://dx.doi.org/10.1006/jcis.2002.8317.
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Yang, Z., X. F. Peng, D. J. Lee, and S. Ay. "Advective flow in spherical floc." Journal of Colloid and Interface Science 308, no. 2 (April 2007): 451–59. http://dx.doi.org/10.1016/j.jcis.2007.01.023.
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Chu, C. P., D. J. Lee, and J. H. Tay. "Floc model and intrafloc flow." Chemical Engineering Science 60, no. 2 (January 2005): 565–75. http://dx.doi.org/10.1016/j.ces.2004.07.132.
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Gorczyca, Beata, and Jerzy Ganczarczyk. "Fractal Analysis of Pore Distributions in Alum Coagulation and Activated Sludge Flocs." Water Quality Research Journal 36, no. 4 (November 1, 2001): 687–700. http://dx.doi.org/10.2166/wqrj.2001.036.
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Abstract The information on floc porosity is essential for estimation of the permeability of the aggregate. The average porosity of alum and activated sludge flocs determined in this study on thin sections of the aggregates was similar, varying in the range from 8 to 9%. Similar porosity of the two different types of aggregates suggested that the permeability of these flocs could also be similar. However, the experimental observations of floc settling rates and floc shape factors did not support this expectation and led to a conclusion that the permeability of an aggregate cannot be estimated based on the average geometric porosity of a floc only. When the size distributions of pores on flocs' sections were analyzed using the concept of fractal geometry, different characteristic values for alum coagulation and activated sludge flocs were found. Larger pore size found in activated sludge flocs allows for more flow through these flocs. Therefore, the size of characteristic pores rather than the average total porosity determines the permeability of an aggregate.
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Boller, Markus, and Stefan Blaser. "Particles under stress." Water Science and Technology 37, no. 10 (May 1, 1998): 9–29. http://dx.doi.org/10.2166/wst.1998.0367.
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The complex nature of particulate matter in natural water resources and in waste waters is characterized by the heterogeneous distribution of particle size, shape, density, and shear strength. Among these parameters, floc strength is most important in the last stages of flocculation. Experimental data on floc strength based on different methods are assessed and correlated with shear gradients in different aquatic environments. The analysis of turbulent motion reveals that the energy which affects particle agglomerates is only a small portion of the totally dissipated energy. Among the different flow fields in turbulent motion, converging/diverging flow cause strain forces which prove to be critical with respect to floc rupture. Model calculations of the surface forces on ellipsoidal particles in pure shear and strain flow fields and corresponding experiments confirm the importance of converging flow. A comparison of modeled and measured rupture forces allows to establish relationships between floc size, strain and shear rates and resulting surface forces leading to probable floc break-up. Flocs of appreciable size (200 - 2000 μm) prepared for settling are likely to be ruptured under moderate velocity gradients occurring in flocculation tanks, whereas smaller agglomerates (< 200 μm) may withstand strain forces much higher than found under practical conditions. An example of model application shows the particle stress in the entrance to porous media filters where typically high strain gradients may easily lead to a breakup of flocs larger than 200 μm.
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Woodfield, D., and G. Bickert. "Separation of flocs in hydrocyclones—significance of floc breakage and floc hydrodynamics." International Journal of Mineral Processing 73, no. 2-4 (February 2004): 239–49. http://dx.doi.org/10.1016/s0301-7516(03)00076-0.
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Jin, Pengkang K., Xiaochang C. Wang, and Haixia Chai. "Evaluation of floc strength by morphological analysis and PDA online monitoring." Water Science and Technology 56, no. 10 (November 1, 2007): 117–24. http://dx.doi.org/10.2166/wst.2007.781.
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This paper established a method for the evaluation of floc strength by morphological analysis and PDA online monitoring. Theoretically, the binding force of a floc can be expressed as B=k1d2Df/3, where k1 is a coefficient, d is floc size and Df is the fractal dimension of the floc. In order to calculate the binding force under a given flocculation condition, a jar test was conducted and d and Df were measured by image analysis. A shear force was exerted on the grown flocs by introducing the flocculated suspension through a transparent tube where the velocity gradient value of the flow could be accurately controlled. As the tube was connected with a particle dispersion analyzer (PDA), the condition of floc breakage was online monitored and the critical condition was identified by analyzing the PDA outputs (FI curves). The binding force coefficient k1 could thus be determined, and the binding force B which represented the floc strength was evaluated. The validity of this method was proved by a series of experiments using aluminium sulphate as coagulant for the flocculation of humic substances.
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Garcia-Aragon, Juan, Ian G. Droppo, Bommanna Krishnappan, Brian Trapp, and Christina Jaskot. "Experimental assessment of Athabasca River cohesive sediment deposition dynamics." Water Quality Research Journal 46, no. 1 (February 1, 2011): 87–96. http://dx.doi.org/10.2166/wqrjc.2011.030.
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Polycyclic aromatic hydrocarbons (PAHs) originating from natural sources, and potentially from the Athabasca Oil Sands development, are of concern for the Athabasca River and Lake Athabasca delta ecosystems. In order to model the transport of fine sediments (and associated PAHs), it is important to describe the sediment dynamics within the river system. Flocs possess different settling characteristics compared to individual particles. A key aspect in modelling floc settling behaviour is the mathematical linkage of the floc density to floc size. In this paper, a rotating annular flume is used to determine the settling characteristics of Muskeg River (a tributary of the Athabasca River) sediments under different shear conditions. Simulations of the settling and flocculation behaviour of these sediments were used to calibrate a density vs. floc size model. A relationship of the parameters relating floc size and density with the fractal dimension F shows that as diameter increases flocs become weaker. Recommendations for the practical application of the model are further formulated in this paper. The deposition tests offer a quantitative measure of the relative amount of sediment that is likely to be transported through the river for given flow conditions.
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Gorczyca, B., and J. Ganczarczyk. "Structure and Porosity of Alum Coagulation Flocs." Water Quality Research Journal 34, no. 4 (November 1, 1999): 653–66. http://dx.doi.org/10.2166/wqrj.1999.034.
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Abstract It is generally assumed that flocs grow according to the following model: primary particles form compact flocculi which assemble themselves into microflocs. Microflocs bind together to form floc aggregates. The main difference between flocculi, microflocs and floc aggregates is their structure. Porosity can be used to indicate differences in this structure. The objective of this study was to establish whether alum flocs disperse into floc components that represent different structures, as indicated by different porosities. Alum coagulation floes were broken up with increasing amounts of mixing energy. The size and porosity of the studied particles were determined on microtome sections of the resin-stabilized samples. The results, as expected, indicated that the size and porosity of alum flocs decreased with the increase of applied mixed energy. Fractal analysis of pores revealed that alum floes contained at least three distinctive populations of pores: small, medium and large. The three pore populations indicate three levels of aggregation, i.e., flocculi, microflocs and floe aggregates. The results of this study confirm the previous theoretical and experimental investigations that argued for the multilevel floc structure.
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Ohno, K., M. Uchiyama, M. Saito, T. Kamei, and Y. Magara. "Practical design of flocculator for new polymeric inorganic coagulant - PSI." Water Supply 4, no. 1 (February 1, 2004): 67–75. http://dx.doi.org/10.2166/ws.2004.0008.
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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.
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Haarhoff, J., and J. K. Edzwald. "Modelling of floc-bubble aggregate rise rates in dissolved air flotation." Water Science and Technology 43, no. 8 (April 1, 2001): 175–84. http://dx.doi.org/10.2166/wst.2001.0492.
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The use of relatively simple, but conceptually sound mathematical models, is a powerful tool to identify and understand parameters that are critical to a process. In this paper, a model is presented which addresses the rise rate of floc-bubble aggregates in the DAF separation zone. The model uses Stoke's Law as a point of departure, which is then progressively extended to incorporate the non-sphericity of the aggregates, the non-laminar nature of their movement, the fractal nature of the flocs, the physical constraints of attaching bubbles to a floc, and the limit on bubble numbers imposed by a typical air dosing system. The main findings are:There are two distinctly different DAF domains, namely a small floc domain and a large floc domain. In the small floc domain, the bubble size, the air volume, chemical dosing and the degree of flocculation have to be optimized and accurately controlled, while the large floc domain is less sensitive to these parameters.The calculated rise rates are significantly lower than some of the latest pilot testing results reported from the USA; a surprising finding at first. There are, however, numerous modelling simplifications that may explain this discrepancy. The most probable reasons are the further agglomeration of the aggregates in the separation zone due to differential rise rates or the recirculating flow within the white-water blanket, and the complex and poorly understood flow patterns within the separation zone.
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Wu, Rome-Ming, Gian-Wei Tsou, Pei-Shan Yen, Duu-Jong Lee, and Xiao-Feng Peng. "Tracking Advective Flow Through Floc Interior." JOURNAL OF CHEMICAL ENGINEERING OF JAPAN 35, no. 6 (2002): 540–46. http://dx.doi.org/10.1252/jcej.35.540.
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Chu, C. P., and D. J. Lee. "Advective flow in a sludge floc." Journal of Colloid and Interface Science 277, no. 2 (September 2004): 387–95. http://dx.doi.org/10.1016/j.jcis.2004.04.036.
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Ding, Yanmei, Jianhai Zhao, Lei Wei, Wenpu Li, and Yongzhi Chi. "Effects of Mixing Conditions on Floc Properties in Magnesium Hydroxide Continuous Coagulation Process." Applied Sciences 9, no. 5 (March 7, 2019): 973. http://dx.doi.org/10.3390/app9050973.
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Magnesium hydroxide continuous coagulation process was used for treating simulated reactive orange wastewater in this study. Effects of mixing conditions and retention time on the coagulation performance and floc properties of magnesium hydroxide were based on the floc size distribution (FSD), zeta potential, and floc morphology analysis. Floc formation and growth in different reactors were also discussed. The results showed that increasing rapid mixing speed led to a decrease in the final floc size. The floc formation process was mainly carried out in a rapid mixer; a rapid mixing speed of 300 rpm was chosen according to zeta potential and removal efficiency. Reducing retention time caused a relatively small floc size in all reactors. When influent flow was 30 L/h (retention time of 2 min in rapid mixer), the average floc size reached 8.06 μm in a rapid mixer; through breakage and re-growth, the floc size remained stable in the flocculation basin. After growth, the final floc size reached 11.21 μm in a sedimentation tank. The removal efficiency of reactive orange is 89% in the magnesium hydroxide coagulation process.
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Coufort, C., and A. Liné. "Hydrodynamic conditioning of aluminium–bentonite flocs." Water Supply 6, no. 1 (January 1, 2006): 11–19. http://dx.doi.org/10.2166/ws.2006.002.
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The aim of this paper is to analyse the role of hydrodynamics in flocculation. The effects of a hydrodynamic sequencing (flocculation–break-up–reflocculation–break-up–reflocculation) on the evolution of aluminium–bentonite floc size distributions and structure are investigated by image analysis in a Taylor–Couette reactor. The flocculation phenomena analysed in this study mainly occur in the viscous subrange, with floc size below the Kolmogorov micro-scale. The high sensitivity of steady-state floc size distribution to initial floc size distribution (elementary particles or flocs formed issuing break-up stages) is highlighted. Reversibility or irreversibility of agglomeration and break-up phenomena are discussed in terms of floc history and hydrodynamic stress. Finally, the hydrodynamic conditioning for aluminium–bentonite flocs is examined.
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Fitzpatrick, C. S. B., E. Fradin, and J. Gregory. "Temperature effects on flocculation, using different coagulants." Water Science and Technology 50, no. 12 (December 1, 2004): 171–75. http://dx.doi.org/10.2166/wst.2004.0710.
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Temperature is known to affect flocculation and filter performance. Jar tests have been conducted in the laboratory, using a photometric dispersion analyser (PDA) to assess the effects of temperature on floc formation, breakage and reformation. Alum, ferric sulphate and three polyaluminium chloride (PACl) coagulants have been investigated for temperatures ranging between 6 and 29°C for a suspension of kaolin clay in London tap water. Results confirm that floc formation is slower at lower temperatures for all coagulants. A commercial PACl product, PAX XL 19, produces the largest flocs for all temperatures; and alum the smallest. Increasing the shear rate results in floc breakage in all cases and the flocs never reform to their original size. This effect is most notable for temperatures around 15°C. Breakage, in terms of floc size reduction, is greater for higher temperatures, suggesting a weaker floc. Recovery after increased shear is greater at lower temperatures implying that floc break-up is more reversible for lower temperatures.
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Jin, Peng Kang, Yong Ning Feng, Jie Xu, and Xian Bao Wang. "The Effect of Polyacrylamide on Floc Structure of Typical Systems." Applied Mechanics and Materials 260-261 (December 2012): 887–90. http://dx.doi.org/10.4028/www.scientific.net/amm.260-261.887.
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Based on that floc structure is an important factor that influencing the coagulation effect and the post-treatment load, the effect of PAM on floc structure of typical system is analyzed and evaluated in this paper. The results show that PAM has a notable influence on floc morphological structure characteristics. For inorganic turbid system, the fractal dimension and diameter of kaolin flocs adding PAM are bigger than that formed by adding aluminum sulfate merely, and the shear-resistant ability of flocs is stronger. With regard to dissolved organic system, adding PAM under two typical pH conditions, the floc morphological characteristic has the same variation with that in inorganic turbid system. PAM could improve the floc morphological structure. However, the improving effect will be relatively weaker under slightly acidic condition, which indicates that the chemical effect of PAM is restrained under this condition. While for the coexisting system, PAM shows an obvious improvement on floc structure under two pH conditions, the floc is compact, bigger and with a higher strength. The chemical effect of PAM is not restrained under slightly acidic condition, which may owe to the interaction between PAM and inorganic suspended materials and dissolved organics in coexisting system.
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Jarvis, P., B. Jefferson, and S. Parsons. "The duplicity of floc strength." Water Science and Technology 50, no. 12 (December 1, 2004): 63–70. http://dx.doi.org/10.2166/wst.2004.0696.
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The breakage of flocs is dependent upon the strength of the bonds holding the aggregate together. The present work describes the breakage and re-growth behaviour of three different types of floc, these were: 1) coagulant precipitate flocs, 2) turbidity flocs and 3) organic matter flocs. Floc aggregates were exposed to increased levels of shear on a conventional jar tester and the sizes of the flocs were observed dynamically using a laser diffraction instrument. The organic flocs showed most resistance to breakage across the whole range of shears under investigation. The dynamic procedure provided detailed information on particle size distributions (PSD). Large and small scale degradation events could be identified from analysis of the PSD data. All of the flocs under investigation showed little re-growth potential after breakage. The precipitate and organic flocs showed slightly better re-aggregation of the small floc sizes.
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Finlayson, J. C., B. Liao, I. G. Droppo, G. G. Leppard, and S. N. Liss. "The relationship between the structure of activated sludge flocs and the sorption of hydrophobic pollutants." Water Science and Technology 37, no. 4-5 (February 1, 1998): 353–57. http://dx.doi.org/10.2166/wst.1998.0664.
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The relationships between the structure of minimally perturbed activated sludge flocs and the sorption of organic contaminants were studied. Sorption, settling velocity, size distributions, floc structure and EPS composition were all examined. The results show significant removal of selected halogenated hydrocarbons and polycyclic aromatic hydrocarbons by biosorption to activated sludge flocs. However, statistically significant effects on the settling or size of the flocs caused by this sorption were not observed. The addition of chromium (Cr(III)) metal ions to the biomass caused observable changes in the floc structure and decreased ruthenium red binding to the acidic polysaccharides of the floc matrix. At low concentrations (0.6 mg/l), chromium caused an increase in the sorption of organic compounds to flocs, suggesting that changes in the floc structure can be induced, which can have an impact on the sorption of pollutants to the flocs.
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Lauri, Janne, Sanna Haavisto, Juha Salmela, Arttu Miettinen, Tapio Fabritius, and Antti I. Koponen. "Online measurement of floc size, viscosity, and consistency of cellulose microfibril suspensions with optical coherence tomography." Cellulose 28, no. 6 (February 18, 2021): 3373–87. http://dx.doi.org/10.1007/s10570-021-03745-6.
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AbstractIn this study, cellulose microfibril (CMF) suspensions were imaged during pipe flow at consistencies of 0.4%, 1.0%, and 1.6% with optical coherence tomography (OCT) to obtain images of the structure and the local velocity of the suspension. The viscosities obtained by combining pressure loss measurement with the OCT velocity data showed typical shear thinning behavior and were in excellent agreement with viscosities obtained with ultrasound velocity profiling. The structural OCT images were used to calculate the radial and the axial floc sizes of the suspension. A fit of power law to the geometrical floc size–shear stress data gave the same power law index for all consistencies, suggesting that floc rupture dynamics is independent of consistency. The dependence of viscosity and floc size on shear stress was similar, indicating that the shear thinning behavior of CMF suspensions is closely related to the rupture dynamics of flocs. The results also showed that an apparent attenuation coefficient of the OCT signal can be used to determine the consistency of CMF suspensions.
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Lee, S. A., T. D. Waite, A. G. Fane, and R. Amal. "Membrane fouling control through aggregate design and trans-membrane pressure selection." Water Supply 2, no. 5-6 (December 1, 2002): 337–43. http://dx.doi.org/10.2166/ws.2002.0188.
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Treatment of waters and wastewaters by microfiltration (MF) requires the addition of chemical coagulants to enhance the removal of dissolved substances. Under these conditions the feed to the MF contains flocculated particulates which must be retained by the membrane. While an extensive knowledge base on the effect of dispersed particles on membrane cake formation and fouling exists, much less information is available on the impact of aggregates on cake characteristics. Results of impact of the size and structure (as characterized by the fractal dimension) of particulate aggregates on microfiltration membrane fouling are in qualitative agreement with a simple model based on the Carman-Kozeny equation. Larger flocs form a cake with large inter-floc porosity which results in a significantly higher permeate flux than achieved for smaller flocs. Concomitantly, looser flocs (of low fractal dimension) are likely to form a cake that has higher intra-floc voidage thus flux is higher than a cake made of compact flocs of similar size. Analysis of cake compression indicates that compressibility is strongly influenced by trans-membrane pressure (TMP). The placement of highly porous aggregates onto the membrane results in formation of a highly porous cake layer provided a low TMP is maintained. Rapid compression of the cake occurs at higher TMPs as shown by the significantly lower porosity of the cake. Under high TMP conditions, the cake porosity exhibits a strong size dependence with larger floc sizes yielding higher porosities. This result possibly indicates formation of relatively impermeable assemblages (as a result of significant compaction) with flux controlled by inter-aggregate flow, i.e. flow around compressed flocs. In comparison, the marked lack of size dependence of porosity at low TMP suggests that permeate flux is dominated by flow through (rather than around) the highly permeable flocs. These results suggest that it should be possible to control both operating conditions (such as TMP) and floc characteristics such that high permeate flux at a given TMP or low cake resistance at a fixed flux is achievable.
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Zhao, Jianhai, Anmin Wang, Lei Wei, Wenqi Ge, Yongzhi Chi, and Yanping Lai. "Effect of kaolin on floc properties for reactive orange removal in continuous coagulation process." Water Science and Technology 78, no. 3 (July 24, 2018): 571–77. http://dx.doi.org/10.2166/wst.2018.327.
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Abstract Magnesium hydroxide was used as a coagulant for treating reactive orange wastewater in a real continuous process. Effects of kaolin on coagulation performance and floc properties were investigated with controlled experiments through floc size distribution, zeta potential, scanning electron microscopy and Fourier transform infrared spectroscopy. Kaolin had significant influence on magnesium hydroxide-reactive orange floc formation and growth. The results showed that average floc size reached 16.31, 12.88 and 20.50 μm, respectively, in the rapid mixer, flocculation basin and sedimentation tank when kaolin concentration was 10 mg/L and reactive orange initial concentration was 0.25 g/L. The floc size tended to increase with the increase of kaolin suspension to 10 mg/L. All of the flocs under investigation showed that floc breakage led to decreased average floc size and remained stable in the flocculation basin. Reactive orange and kaolin could be removed effectively in the continuous coagulation process. Reactive orange was adsorbed in the surface of magnesium hydroxide through charge neutralization and adsorption.
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Zhao, Bingqing, Dongsheng Wang, Tao Li, and Chihpin Huang. "Effect of floc structure and strength on membrane permeability in the hybrid coagulation-microfiltration process." Water Supply 11, no. 1 (March 1, 2011): 97–105. http://dx.doi.org/10.2166/ws.2011.014.
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The relative importance of floc property on microfiltration and fouling mechanism remains a field of arguments. The effects of floc structure and strength on fouling rate of coagulation-microfiltration were investigated in dead-end microfiltration. Flocs varying in size, fractal structure and strength were prepared by AlCl3 and PACl (Polyaluminum Chloride) coagulation at various dosages followed by different slow mixing rates and filtration without any sedimentation step. The rates of flux decline for flocs formed under same coagulant dosage but different shear conditions showed only limited size and compactness dependence. However, the floc strength effect on membrane filtration performance was observed clearly with the floc strength constant exhibiting a strong positive linear correlation with the resulted cake compressibility index.
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Zhu, Zhongfan. "A formula for the settling velocity of cohesive sediment flocs in water." Water Supply 19, no. 5 (January 16, 2019): 1422–28. http://dx.doi.org/10.2166/ws.2019.007.
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Abstract A simple formula is developed to relate the size and settling velocity of cohesive sediment flocs in both the viscous and inertial settling ranges. This formula maintains the same basic structure as the existing formula but is amended to incorporate the fact that the flocculated sediment has an internal fractal architecture and is composed of different-sized primary particles. The input parameters needed for calculating the settling velocity include the median size and size distribution of the primary particles, the fractal dimension of the floc, the density of the sediment, and two calibrated coefficients that incorporate the effects of floc shape, permeability, and flow separation on drag. The proposed formula is compared with four data sets of settling velocity–floc size collected from the published literature, and a good agreement between the model and these data can be found.
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Liu, Linshuang, Guolu Yang, and Minghui Yu. "Simulation for Sludge Flocculation I: Brownian Dynamic Simulation for Perikinetic Flocculation of Charged Particle." Mathematical Problems in Engineering 2012 (2012): 1–17. http://dx.doi.org/10.1155/2012/527384.
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To investigate sludge drying process, a numerical simulation based on Brownian dynamic for the floc with uncharged and charged particles was conducted. The Langevin equation is used as dynamical equation for tracking each particle in a floc. An initial condition and periodic boundary condition which well conformed to reality is used for calculating the floc growth process. Each cell consists of 1000 primary particles with diameter 0.1 ∼ 4 μm. Floc growth is related to the thermal force and the electrostatic force. The electrostatic force on a particle in the simulation cell is considered as the sum of electrostatic forces from other particles in the original cell and its replicate cells. It is assumed that flocs are charged with precharged primary particles in dispersion system by ionization. By the analysis of the simulation figures, on one hand, the effects of initial particle size and sludge density on floc smashing time, floc radius of gyration, and fractal dimension were discussed. On the other hand, the effects of ionization on floc smashing time and floc structure were presented. This study has important practical value in the high-turbidity water treatment, especially for sludge drying.
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Vesga-Rodríguez, Claudia Patricia, Leonardo David Donado-Garzón, and Monroe Weber-Shirk. "Evaluation of high rate sedimentation lab-scale tank performance in drinking water treatment." Revista Facultad de Ingeniería Universidad de Antioquia, no. 90 (December 14, 2018): 9–15. http://dx.doi.org/10.17533/udea.redin.n90a02.
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The Cornell University AguaClara program researches ways to improve the process of potable water treatment at low cost and no energy dependent. A High Rate Sedimentation (HRS) process that uses upward flow and less area than traditional tanks was investigated. The objective was to analyze parameters affecting HRS tank performance including velocity, density of the floc blanket and location of plate settlers in a laboratory scale HRS tank. Different velocities were set during the experiment, and the resulting performance of the floc blanket was evaluated through continuous turbidity measurements. Results demonstrated that the lab-scale tank allows the creation of a floc blanket and is a versatile design with constraints of visibility and accessibility. In addition, performance of the sedimentation tank improves at lower up flow velocities; however, the study suggests that plate settlers at the top of the tank stabilized the floc blanket at higher velocities, as a consequence of denser floc blankets created by the plates.
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Li, B., and P. Bishop. "Structure-function dynamics and modeling analysis of the micro-environment of activated sludge floc." Water Science and Technology 47, no. 11 (June 1, 2003): 267–73. http://dx.doi.org/10.2166/wst.2003.0614.
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Biodegradation by microorganisms and mass transfer resistance in the micro-environment of activated sludge floc can cause changes in substrate and dissolved oxygen concentrations within the floc and can contribute to stratification of microbial processes inside the flocs. In this study, an integrated model of the microenvironment of the activated sludge floc was developed for floc from wastewaters from several sources and of varying strengths for dynamic simulation of the combined biological processes of COD and nitrogen removal. The model simulation results and measured profiles show the heterogeneous and gradient-governed microenvironment of activated sludge floc under different substrate and bulk oxygen concentrations. The substrate concentration increase zones inside the floc were present in all activated sludge floc from the Miller Brewing Co. wastewater treatment facility (high pollutant strength), with an oxygen penetration depth of only 0.15 mm into the outer layer. The anoxic and substrate concentration increase zones also dominated in the activated sludge floc from the Mill Creek Plant influent (medium pollutant strength), with the outer layer (0.20 mm) participating in the metabolism of the pollutants. The radius of the substrate concentration increase zone inside the sludge floc decreased with pollutant removal along the length of the tank. When the pollutant concentration in the bulk wastewater was low (Muddy Creek Plant), the substrate concentration increase zone disappeared; the whole floc was aerobic and in a high redox status. Our experiments and model analyses demonstrate that the microorganisms' structure-functions inside activated sludge floc change with the bulk substrate concentration and dissolved oxygen concentration.
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Krishnappan, B. G., J. Marsalek, W. E. Watt, and B. C. Anderson. "Seasonal size distributions of suspended solids in a stormwater management pond." Water Science and Technology 39, no. 2 (January 1, 1999): 127–34. http://dx.doi.org/10.2166/wst.1999.0103.
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Three seasonal surveys of suspended solids were carried out in an on-stream stormwater management pond, by means of a submersible laser particle size analyser. Size distributions were measured at up to 17 points in the pond, and water samples collected at the same locations were analysed for primary particles aggregated in flocs. Observed suspended solids were mostly composed of flocs, with maximum sizes ranging from 30 to 212 μm for winter and summer surveys, respectively. Using a relationship defining the floc density as a function of floc size and Stokes' equation for settling, an empirical relationship expressing the floc fall velocity as a function of floc size was produced. This relationship indicates that naturally formed flocs in the size range from 5 to 15 μm would settle faster than both smaller primary particles of higher density, and somewhat larger flocs of lower density, which are however susceptible to break up by turbulence.
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François, R. J., and A. A. Van Haute. "The Role of Rapid Mixing Time on a Flocculation Process." Water Science and Technology 17, no. 6-7 (June 1, 1985): 1091–101. http://dx.doi.org/10.2166/wst.1985.0204.
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The influence of the duration of rapid mixing on a flocculation process is evaluated by investigating the characteristics of the hydroxide flocs formed under carefully controlled conditions. Two different methods are used for measuring floc dimensions and their distribution. From the experimental results other floc characteristics such as floc strength and size of the flocculi are deduced. Also the reaction constant, the destabilization factor and the growing constant of the coagulation and flocculation process are calculated. Using the influence of rapid mixing time on all floc characteristics and kinetic parameters minimum and maximum limits for the rapid mixing time are deduced.
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Moon, B. H., G. T. Seo, T. S. Lee, S. S. Kim, and C. H. Yoon. "Effects of salt concentration on floc characteristics and pollutants removal efficiencies in treatment of seafood wastewater by SBR." Water Science and Technology 47, no. 1 (January 1, 2003): 65–70. http://dx.doi.org/10.2166/wst.2003.0017.
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Most seafood wastewater has been treated by the activated sludge process. Due to changes in salt concentration, pollutant loadings and raw materials, the process is not operated satisfactorily to meet effluent regulation. Most problems faced at present are solid liquid separation. In this study, effects of salt concentration on floc characteristics and pollutants removal efficiencies were investigated in treatment of seafood wastewater by SBR. For analyzing fractal dimension of flocs, the small angle laser light scattering (SALLS) method was applied using a Diffraction Particle Sizer (Malvern Instruments). Organic removal efficiencies (in terms of CODMn) decreased with increasing salt concentration, but eventually reached a steady state. Fractal dimension and floc size also showed similar trends with changing salt concentration. The main reasons to reduced pollutant removal efficiencies were deteriorated biological activity and settling properties. The biological activity was affected faster than the floc characteristics by increasing salt concentration. The deteriorated settling properties were explained by decreased size and fractal dimension of floc due to increasing salt concentration. The settling properties of floc such as sludge volume index (SVI) and zone settling velocity (ZSV) were related to size and fractal dimension of floc. The fractal dimension of floc was better related to the settling properties than the size of floc.
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Ehlers, G. A. C., D. Wagachchi, and S. J. Turner. "Nutrient conditions and reactor configuration influence floc size distribution and settling properties." Water Science and Technology 65, no. 1 (January 1, 2012): 156–63. http://dx.doi.org/10.2166/wst.2011.849.
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Floc formation and settleability is critical for effective solid–liquid separation in many wastewater treatment processes. This study aimed to investigate the relationship between particle size distribution and nutrient conditions in different bioreactor configurations. Size distribution profiles of flocs that formed in continuous (B1), continuous with clarifier and return sludge (B2) and SBR (B3) reactors were investigated in parallel under identical nutrient conditions. An eight-fold dilution of the influent COD of a synthetic dairy processing wastewater resulted in a ‘feast and famine’ regime that triggered significant effects on the biomass and flocculation characteristics. Floc size analysis of reactor MLSS revealed a shift in floc sizes when reactors were fed with the minimum (famine) COD wastewater feed (0.61 g L−1). Increasing floc size distributions were detected for all reactors during the minimum COD feed although different size patterns were observed for different reactor configurations. These increases corresponded with variations in aggregation and EPS quantities. The SBR yielded comparatively larger flocs when operated under both COD feeds as indicated by d(0.9) values (90% of particles ≤ d in size). Overall the results indicated that floc formation and floc size are mediated by nutrient concentrations and represents an important step towards improved solid–liquid separation.
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Ding, Shi Qiang, Yuan Yuan Wei, Xin Rong Pang, and Ji Run Xu. "A Research on the Morphology and Composition of Flocs (Part 2: Floc Breakage Included)." Advanced Materials Research 726-731 (August 2013): 1585–90. http://dx.doi.org/10.4028/www.scientific.net/amr.726-731.1585.
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The floc breakage plays an important role in the flocculation, the stable floc size or morphology distribution is the result of the equilibrium of formation and breakage. In this paper, the breakage approaches or models for different kind and size of flocs have been discussed. By introducing special breakage functions and comparing their relative values, the numbers of various flocs are verified to be still proportional to the suspension concentration compared with the situation in which the breakage is neglected. However, as illustrated in this paper, the total number of every kind of floc is still a power function of the suspension concentration for dilute suspensions where the number concentration of solid particles is linearly related to the volume concentration. This is similar to that where the breakage is disregarded, although the number for every kind of floc is inevitably changed. In addition, a potential quantitative method to analyze the relative composition of different kinds of flocs is presented by measuring the contributions of the flocs to the suspension viscosity.
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Liu, Xinliang, Hailiang Yin, Jian Zhao, Ziqi Guo, Zhen Liu, and Yizhou Sang. "Understanding the coagulation mechanism and floc properties induced by Fe(VI) and FeCl3: population balance modeling." Water Science and Technology 83, no. 10 (April 19, 2021): 2377–88. http://dx.doi.org/10.2166/wst.2021.150.
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Abstract Coagulation kinetics and floc properties are of great fundamental and practical importance in the field of water treatment. To investigate the performance of Fe(VI) and Fe(III) salt on particle coagulation, Malvern Mastersizer 2000 was employed to continuously and simultaneously monitor the kaolin floc size and structure change, and population balance modeling was used to investigate the coagulation mechanism. The results show dosage increase had positive effect on collision efficiency and floc strength and negative effect on restructure rate. Low shear rate resulted in higher collision efficiency and stronger floc. Low water temperature had a pronounced detrimental effect on coagulation kinetics. Temperature increase showed the most significant positive effect on collision efficiency, floc strength and restructure rate. The optimum pH zone for the coagulation was found to be between 6 and 8. Further pH increase lowered the collision efficiency and floc strength and increased the restructure rate. FeCl3 resulted in a larger ratio of the mass to volume of kaolin flocs (compactness) than those induced by ferrate.
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Jiwani, Ashifa, Nigel J. D. Graham, and Martin C. Day. "Activated sludge process control via particle monitoring." Water Science and Technology 36, no. 4 (August 1, 1997): 269–77. http://dx.doi.org/10.2166/wst.1997.0135.
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The interrelationships between activated sludge plant operation and floc characteristics were examined in order to determine process control mechanisms for the effective treatment of domestic wastewaters and surplus activated sludge. A quantitative indicator of the physiological floc characteristics was developed and termed the morphological index. This may be evaluated by plant operators using a simple assessment form and matching photographic guide of various floc structures. The morphological index and floc size distribution were found to be useful tools for activated sludge process control and monitoring the dewaterability of surplus activated sludge. It was found that floc size, morphology and in turn the dewaterability of surplus activated sludge varied with different operating conditions. Hydraulic retention times (HRTs) of < 10 hours and sludge ages of ≤8 days, resulted in the presence of small diffuse floc structures in the mixed liquor. The effluent quality was poor and the activated sludge had unfavourable filtering and dewatering properties. Switching plant operation to sludge ages in the region of ≥8 days and HRTs of ≥10 hours, was found to improve effluent quality and the dewaterability of surplus activated sludge. Here the flocs were large compact structures with short filaments protruding from the floc body.
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Tsai, CH, and SC Hwang. "Flocculation of sediment from the Tanshui River estuary." Marine and Freshwater Research 46, no. 1 (1995): 383. http://dx.doi.org/10.1071/mf9950383.
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Experiments on the flocculation of fine-grained sediments from the Tanshui River estuary, Taiwan, were carried out. The effects of fluid shear, sediment concentration and salinity on floc growth were investigated. The ranges of these parameters were 12.5 to 400 s-1 for the shear, 50 to 600 mg L-1 for the sediments concentration and 0% to 100% sea water for the salinity. The results showed the following. (1) The time required to reach a steady state ranges from 2 to 44 h and median floc sizes range from 100 to 520 μm. (2) The steady-state median floc size decreases with the increase in sediment concentration. (3) The floc size increases as the shear increases. (4) Increasing the proportion of sea water from 0% to 50% decreases the floc size to one-fourth of that of freshwater flocs, and a further increase in salinity does not decrease floc size significantly. (5) The time required to reach a steady state decreases with the decrease in shear, the increase in sediment concentration and the increase in salinity. (6) The larger the steady-state flocs, the longer they take to form. Comparison of these results with those obtained in similar studies of Lake Erie sediments shows that the flocculation properties of Tanshui sediments are substantially different from those of Lake Erie sediments. Tanshui sediments are much more difficult to aggregate, but once flocs are formed they are larger. The reasons why different types of sediment behave differently should be studied further.
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Nielsen, P. H., T. R. Thomsen, and J. L. Nielsen. "Bacterial composition of activated sludge - importance for floc and sludge properties." Water Science and Technology 49, no. 10 (May 1, 2004): 51–58. http://dx.doi.org/10.2166/wst.2004.0606.
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Activated sludge flocs consist of numerous constituents which, together with other factors, are responsible for floc structure and floc properties. These properties largely determine the sludge properties such as flocculation, settling and dewaterability. In this paper we briefly review the present knowledge about the role of bacteria in relation to floc and sludge properties, and we present a new approach to investigate the identity and function of the bacteria in the activated sludge flocs. The approach includes identification of the important bacteria and a characterization of their physiological and functional properties. It is carried out by use of culture-independent molecular biological methods linked with other methods to study the physiology and function, maintaining a single cell resolution. Using this approach it was found that floc-forming properties differed among the various bacterial groups, e.g. that different microcolony-forming bacteria had very different sensitivities to shear and that some of them deflocculated under anaerobic conditions. In our opinion, the approach to combine identity with functional analysis of the dominant bacteria in activated sludge by in situ methods is a very promising way to investigate correlations between presence of specific bacteria, and floc and sludge properties that are of interest.
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Ding, Shi Qiang, Qing Na Li, Xin Rong Pang, and Ji Run Xu. "A Research on the Morphology and Composition of Flocs (Part 1: Floc Breaage Disregarded)." Advanced Materials Research 726-731 (August 2013): 1566–72. http://dx.doi.org/10.4028/www.scientific.net/amr.726-731.1566.
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The characteristics of flocs aggregated in flocculation have been paid more and more attention for a long time. In this paper, a new classification and analyses method dealing with the flocs is developed. The flocs formed after flocculation is divided into four kinds, including the left primary particles, linear flocs with all component particles in a line, planar flocs with all component particles on a plane and volumetric flocs with all component particles in a three-dimensional space. By analyzing the formation approaches of different kind of flocs regardless of the floc breakage, the number of every kind of floc is analyzed to be related with the suspension concentration mathematically. After comparing the different items in the models describing the relationship of floc number and concentration, a series of simplified expressions are presented. Lastly, a mathematical equation relating the measurable suspension viscosity with the numbers of different flocs is obtained.
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Gorczyca, Beata, and Paul Klassen. "Optimization of Solids Separation in Dissolved Air Flotation." Water Quality Research Journal 43, no. 2-3 (May 1, 2008): 239–47. http://dx.doi.org/10.2166/wqrj.2008.027.
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Abstract Sizes of flocs were analyzed to identify characteristics of the particle size distribution optimal for separation by dissolved air flotation (DAF). Optical microscopes and two particle counters were used for floc sizing. A Brightwell Technologies particle counter was found to provide floc size measurements in agreement with improved microscopic methods. The particle counter provided distribution of flocs with sizes down to 1 micron (µm). This allowed for inclusion of flocs with size ranging from 5 to 1 µm, which were excluded from the analyses in the earlier study. Four alum dosages were applied: 15, 25, 40, and 60 mg/L. The turbidity and colour of the DAF effluent at alum dosages of 25, 40, and 60 mg/L were very similar. However, the analysis of the flocs in the treated effluent revealed that, at the alum dose of 60 mg/L, particle removal was the best. Therefore, this dosage was selected as optimal for the solid/liquid separation process. The average size of coagulation flocs at 60 mg/L was approximately 30 µm, and was equal to the estimated size of air bubbles produced by the saturator. Therefore, this study confirms the finding of the earlier work claiming that the optimum DAF performance is attained when the mean floc size and the bubble size are equal. Similar size of floc and bubble indicates that flocs act predominantly as nuclei for bubble formation. This finding contributes to the knowledge of mechanisms of floc air bubble attachment in DAF.
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Lin, Qintie, Huanlong Peng, Qinlu Lin, and Guangcai Yin. "Formation, breakage and re-formation of flocs formed by cationic starch." Water Science and Technology 68, no. 6 (September 1, 2013): 1352–58. http://dx.doi.org/10.2166/wst.2013.377.
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The efficiency of flocculation can be significantly improved through floc breakage and re-formation under appropriate conditions. To obtain a better understanding of the mechanisms involved and to relate floc properties to separation efficiency, the effects of mixing conditions on the formation, breakage and re-formation of flocs formed by kaolin and cationic starch were investigated through conventional jar test procedure and continuous optical monitoring. It has been found that the breakage of flocs was fully reversible and the polymer flocculant could resist strong shear; even having been sheared for four times, the flocculation index (FI) value would be higher than that of the original flocs. The results indicated flocs formed at neutral and alkaline conditions had better shear resistance than those at acidification conditions, and the mode of floc rupture was large-scale fragmentation.
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Kim, Sang-Soo, Byung-Hyun Moon, Gyu-Tae Seo, and Cho-Hee Yoon. "The effects of starvation on physical characteristics of flocs in SBR for treating saline wastewater." Water Science and Technology 56, no. 7 (October 1, 2007): 41–46. http://dx.doi.org/10.2166/wst.2007.691.
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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 < floc size and fractal dimension < T-N removal < T-P removal.
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Bache, D. H., C. Johnson, J. F. McGilligan, and E. Rasool. "A conceptual view of floc structure in the sweep floc domain." Water Science and Technology 36, no. 4 (August 1, 1997): 49–56. http://dx.doi.org/10.2166/wst.1997.0084.
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Using a model suspension of rice starch granules coagulated with alum, the paper describes an experimental investigation into the factors which control strength by the sweep floc mechanism. Electron micrographs, backed by electrophoresis measurements, indicated that the precipitate exists both as a positively charged adhesive coating and also in a mobile state, possibly similar to ‘free’ precipitate without significant charge. A comparison of strength measurements on flocs derived from rice starch with those based on low charged latex particles, led to the conclusion that coulombic attraction between the primary charges and shared coating in the form of an electrostatic bridge was the dominant bonding mechanism when the primary charge was significant. Rheological measurement on a suspension of the ‘free’ precipitate at a concentration likely to be encountered within the floc showed that it behaved as a Bingham plastic i.e with an identifiable yield stress at zero shear and contributes to cohesion. It is suggested that floc strength depends on an interplay between these two binding mechanisms, overdosing reducing electrostatic bridging and tending towards the weaker cohesion of the internal gel.
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Chu, K. H., H. M. van Veldhuizen, and M. C. M. van Loosdrecht. "Respirometric measurement of kinetic parameters: effect of activated sludge floc size." Water Science and Technology 48, no. 8 (November 1, 2003): 61–68. http://dx.doi.org/10.2166/wst.2003.0453.
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The variation of activated sludge floc size with the mixing intensity of a mechanically stirred respirometer, expressed in terms of the mean energy dissipation rate, was characterized using a photometric dispersion analyzer. The floc size decreased rapidly when the energy dissipation rate was increased from 1.33 × 10-3 to 2.68 × 10-3 W/kg. Experiments were performed to investigate the effect of floc size on the oxygen saturation coefficient measured under the condition of acetate oxidation. The respirometric data were interpreted by considering only the kinetics of biochemical reactions. The variation of the oxygen saturation coefficient with mixing intensity was found to correlate with the variation of floc size with mixing intensity. The oxygen saturation coefficient was found to decrease from 0.23 to 0.08 mg/L when the mean energy dissipation rate was increased from 1.33 × 10-3 to 2.68 × 10-3 W/kg. The dependence of the oxygen saturation coefficient on floc size or mixing intensity suggests the presence of mass transfer resistances in large flocs.