Characterization of Agitation Intensity in Flocculation Processes

Glasgow, Larry A.; Kim, Y. H.

doi:10.1061/(asce)0733-9372(1986)112:6(1158)

Cited by 16 publications

(2 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although 100 per cent flocculation was not reached in the OBR, a comparison with another study [90] demonstrated that, for similar starting bacterial concentrations, fuller flocculation was achieved in the OBR at much lower shear rates. Previous authors have commented on the non-homogeneous nature of STRs that results in floc break-up near the impeller zone where shear rates can be two orders of magnitude higher than the average [91]. The more even shear distribution in OBRs [33] allows flocculation to occur at much lower average shear providing an attractive, alternative flocculation device to STRs [75].…”

Section: Bioprocesses Using Cellular Componentsmentioning

confidence: 99%

Biological processing in oscillatory baffled reactors: operation, advantages and potential

Harvey

et al. 2013

Interface Focus.

View full text Add to dashboard Cite

The development of efficient and commercially viable bioprocesses is essential for reducing the need for fossil-derived products. Increasingly, pharmaceuticals, fuel, health products and precursor compounds for plastics are being synthesized using bioprocessing routes as opposed to more traditional chemical technologies. Production vessels or reactors are required for synthesis of crude product before downstream processing for extraction and purification. Reactors are operated either in discrete batches or, preferably, continuously in order to reduce waste, cost and energy. This review describes the oscillatory baffled reactor (OBR), which, generally, has a niche application in performing ‘long’ processes in plug flow conditions, and so should be suitable for various bioprocesses. We report findings to suggest that OBRs could increase reaction rates for specific bioprocesses owing to low shear, good global mixing and enhanced mass transfer compared with conventional reactors. By maintaining geometrical and dynamic conditions, the technology has been proved to be easily scaled up and operated continuously, allowing laboratory-scale results to be easily transferred to industrial-sized processes. This is the first comprehensive review of bioprocessing using OBRs. The barriers facing industrial adoption of the technology are discussed alongside some suggested strategies to overcome these barriers. OBR technology could prove to be a major aid in the development of commercially viable and sustainable bioprocesses, essential for moving towards a greener future.

show abstract

Section: Bioprocesses Using Cellular Componentsmentioning

confidence: 99%

Biological processing in oscillatory baffled reactors: operation, advantages and potential

Harvey

et al. 2013

Interface Focus.

View full text Add to dashboard Cite

show abstract

“…Obvious examples include paddle-flocculation basins, upflow clarifiers, and aeration tanks in bioflocculation. The stirred, baffled tank has been studied by Holmes et al (1964), Cutter (1966), Rao and Brodkey (1972), Okamoto et al (1981), Placek and Tavlarides (1985), and Glasgow and Kim (1986) among others. The impeller stream is of primary interest for it has been shown that the dissipation rate there can exceed the mean tank value by as much as 2 orders of magnitude.…”

Section: Tank Hydrodynamicsmentioning

confidence: 99%

Simulation of aggregate growth and breakage in stirred tanks

Kim¹,

Glasgow²

1987

Ind. Eng. Chem. Res.

Self Cite

View full text Add to dashboard Cite

Successful modeling of the dynamic behavior of the particle-size distribution in coagulation and wastewater treatment processes is necessary for improved understanding and design of flocculation operations. At present, both probabilistic and stochastic modeling efforts are constrained by the lack of accurate information regarding the breakage mode and fragment-size distribution and the interaction between these quantities and hydrodynamics. Indeed, many prior modeling efforts have been based upon breakage mechanisms that are quite erroneous for inhomogeneous turbulent flow fields. The objectives of this work are to demonstrate the true nature of floc breakage in turbulence, to show that deterministic models are quite inappropriate, and to provide a means for the simulation of batch flocculation experiments.The significance of floc breakage to the operation of treatment processes appears to have been appreciated as early as 1960; now any operator familar with lost solids over the weir in bioflocculation or shortened filtration runs in domestic water production can describe the symptoms of floc disintegration. As investigators began to look at the problem, it was natural to start with kinetic descriptions that simply reversed Smoluchowski's (1917) orthokinetic model for the rate of removal of primary colloidal particles; for example, Healy and La Mer (1964) suggested that floc-size reduction occurred by primary particle erosion as a consequence of surface shear. In contrast, Thomas (1964) advocated bulgy pressure deformation and rupture in analogy with existing theories of droplet breakage in emulsification. The idea that a definite relation must exist between parent aggregation size and the scale by turbulent eddies responsible for disintegration was put forward by Parker et al. (1972). Matters were further complicated when Ham and Christman (1969) offered experimental evidence of breakage caused by floc-floc collisions. In retrospect, any theory of floc disintegration based upon primary particle liberation should have been viewed with suspicion; since Michaels and Bolger (1962) and Vold (1963) had described the process of floc-floc collisions leading to what is generally called "multiple-level" aggregation, it was apparent that breakage would produce a broad spectrum of fragment sizes. Furthermore, the turbulent energy necessary for disintegration is simply not available at small scales. Eddies comparable to the Kolmogorov microscale are not capable of removing individual particles from the small floc structures except under the most peculiar circumstances.The first direct evidence of the true nature of floc disintegration was probably the experimental investigation reported by Glasgow and Hsu (1982). In this work, photographs of individual floc-breakage events caused by a turbulent jet showed a very broad distribution of daughter particle sizes; it was also shown that the disintegrations could generally be classified as either "thorough" or "erosive". Binary breakage, ever popular with theorists, was not found ...

show abstract

Fluid‐Borne entities in the impeller stream of a rushton turbine

Glasgow¹

2000

Can J Chem Eng

Self Cite

View full text Add to dashboard Cite

he breakage or disintegration of fluid-borne entities in stirred tanks is a key operation in the chemical process industries. But T because flow in stirred tanks is inhomogeneous and complex, no general method has been put forward that permits quantitative evaluation of size reduction events. The location of the interaction between a fluid-borne entity and the impeller stream largely determines the outcome of the encounter, and many other variables including size, density, and shape affect it. Calabrese and Stoots (1989) noted that globules, flocs, and fragile particles disintegrate in response to forces arising from the vortex system trailing the impeller blades, or from the region where the vortex system breaks down. This is generally confirmed by observation; for example, Chang et al.(1 981) demonstrated that the dispersion of oil in water can occur by stretching (and subsequent ejection) as oil drops flow over and around an oncoming turbine blade. Work carried out in our laboratory also shows that the deformation of large drops of a neutrally-buoyant oil dispersed in water can occur well out into the impeller stream as the entitiy is entrained in the impeller discharge.The performance of the Rushton turbine in mixing processes, emulsification, and chemical reactor operation has been the subject of intense examination for 40 years. Measurements of velocities and velocity vector orientation, as well as estimates of dissipation rate, have appeared in the literature; these efforts span the decades from Sachs and Rushton (1 954) to Lee and Yianneskis (1 998). The range and scope of the contributions can be gauged by consulting one of the excellent published reviews such as Chapter 4 in Tatterson 286The breakage or disintegration of suspended entities by energetk fluid motions in stirred tanks is an essential aspect of many operations in the chemical process industries. However, the hydrodynamic inhomogeneity of such tanks makes it extremely difficult to characterize the stresses experienced in any simple manner. This work provides a determination of both the location and the frequency of interaction of spherical fluid-borne entities with the discharge of a Rushton turbine. These data show how both particle size and impeller speed affect the severity of the exposure, setting the groundwork for improved descriptions of the dynamic behaviour of the particle size distribution in a wide variety of dispersed-phase processes.La rupture ou la desindgration de particules suspendues par des deplacements de fluides Cnergetiques dans des reservoirs agitCs est un aspect essentiel de nombreuses operations des industries de proc&des chimiques. Toutefois, la non-homogdnkite hydrodynamique de ces reservoirs rend exMmement difficile la caracterisation des forces en jeu par une methode simple. On determine dans ce travail la position et la frequence d'interaction de particules sphkriques transpottees par le fluide dans la zone de refoulement d'une turbine Rushton. Ces donnees montrent comment la taille des particules et la vitesse ...

show abstract

Characterization of Agitation Intensity in Flocculation Processes

Cited by 16 publications

References 7 publications

Biological processing in oscillatory baffled reactors: operation, advantages and potential

Biological processing in oscillatory baffled reactors: operation, advantages and potential

Simulation of aggregate growth and breakage in stirred tanks

Fluid‐Borne entities in the impeller stream of a rushton turbine

Contact Info

Product

Resources

About