Monitoring floc formation and breakage

2004 ◽  
Vol 50 (12) ◽  
pp. 163-170 ◽  
Author(s):  
J. Gregory
Keyword(s):  
Shear Rate ◽  
Practical Importance ◽  
Cationic Polyelectrolyte ◽  
Optical Monitoring ◽  
Limited Extent ◽  
Marked Contrast ◽  
Adequate Model ◽  
Monitoring Technique ◽  
Convenient Means ◽  
Floc Breakage

Monitoring of flocculation processes is of great practical importance and can give very useful information on the action of different coagulants under various conditions. It is shown that a continuous optical monitoring technique provides a convenient means of following the formation, break-up and regrowth of flocs under standard mixing and stirring conditions. Examples of results using this approach are given, with alum and PACl coagulants as well as a cationic polyelectrolyte. PACl products give larger flocs than with alum, but they show about the same relative degree of breakage when the shear rate is increased. With all of these coagulants, floc breakage is not fully reversible; i.e. flocs only re-grow to a limited extent when the shear rate is reduced. This is in marked contrast to the action of a cationic polyelectrolyte, where floc breakage is almost completely reversible. Some possible reasons for these observations are discussed, but, so far, there is no adequate model available.

Properties of flocs formed using different coagulants

2002 ◽  
Vol 2 (5-6) ◽  
pp. 95-101 ◽  
Author(s):  
M.A. Yukselen ◽  
J. Gregory
Keyword(s):  
Shear Rate ◽  
Continuous Monitoring ◽  
Test Procedure ◽  
Cationic Polyelectrolyte ◽  
Aluminium Sulphate ◽  
Jar Test ◽  
Average Shear ◽  
Break Up ◽  
Polyaluminium Chloride ◽  
Floc Breakage

The effects of shear on the formation and break-up of flocs generated using aluminium sulphate (“alum”), polyaluminium chloride and a cationic polyelectrolyte have been investigated using conventional jar test procedure and by continuous optical monitoring. Using the experimentally determined optimum dosage, the breakage of flocs was followed at a high stirring speed, corresponding to average shear rate (G) of about 330-520 s-1. Most of the breakage occurred within a few seconds of increasing the shear rate. After each breakage the stirring rate was reduced to the original value to allow the flocs to re-grow. For alum and polyaluminium chloride, it was found that only limited re-growth of flocs occurred indicating a significant irreversibility of the floc break-up process. Residual turbidity increased after floc breakage and re-growth, indicating a reduction in sedimentation rate of the re-grown flocs, consistent with the continuous monitoring results. For the cationic polyelectrolyte, the re-growth of flocs occurred to a much greater extent and floc breakage was almost fully reversible.

Defect Nucleation and Annihilation in Sheared Polymeric Liquid Crystals

2002 ◽  
Vol 734 ◽  
Author(s):  
Dana Grecov ◽  
Alejandro D. Rey
Keyword(s):  
Liquid Crystals ◽  
Shear Rate ◽  
Long Range ◽  
Short Range ◽  
Practical Importance ◽  
Topological Defects ◽  
Annihilation Rate ◽  
Shear Rates ◽  
Parallel Array ◽  
Defect Nucleation

ABSTRACTShear–induced nucleation and annihilation of topological defects due to hydrodynamic instability in nematic liquid crystals is a phenomenon of both scientific interest and practical importance. We use a complete generalized non-linear second order tensor Landau-de Gennes model that takes into account short range order elasticity, long-range elasticity and viscous effects, to simulate the nucleation and annihilation of twist inversion walls in flow-aligning nematic polymers subjected to shear flow. Shearing a homogeneous nematic sample perpendicular to the director results in an linear instability that maybe symmetric at low shear rates, and antisymmetric at higher shear rates. At even higher shear rates the onset of nonlinearities results in the nucleation of a parallel array of twist inversion walls, such that asymmetry prevails. By increasing the shear rate the following director symmetry transition cascade is observed: symmetric → antisymmetric → asymmetric → symmetric. The nucleation of the parallel array of twist inversion walls in the asymmetric mode is due to the degeneracy in reorientation towards the shear plane. The annihilation of twist walls is mediated by twist waves along the velocity gradient direction. Twist walls annihilate by three mechanisms: wall-wall annihilations, wall-wall coalescence, and wall-bounding surface coalescence. The annihilation rate increases with increasing shear rate and at sufficiently high rates the layered structure is replaced by a homogeneously aligned system. The role of short range and long range elasticity on defect nucleation and annihilation is characterized in terms of the Deborah and Ericksen numbers. Close form solutions to approximated equations are used to explain the numerical results of the full Landau-de Gennes equations of nematodynamics.

Formation and breakage of flocs using dual polymers

2006 ◽  
Vol 53 (7) ◽  
pp. 217-223 ◽  
Author(s):  
M.A. Yukselen ◽  
J. Gregory ◽  
E. Soyer
Keyword(s):  
Shear Rate ◽  
Test Procedure ◽  
Optical Monitoring ◽  
Ionic Polymers ◽  
Ionic Polymer ◽  
Polymer Addition ◽  
Anionic Polymers ◽  
Jar Test ◽  
Average Shear ◽  
Floc Strength

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

Effect of tapering on the break-up and reformation of flocs formed using hydrolyzing coagulants

2006 ◽  
Vol 6 (2) ◽  
pp. 139-145 ◽  
Author(s):  
M.A. Yukselen ◽  
K.R. O'Halloran ◽  
J. Gregory
Keyword(s):  
Velocity Gradient ◽  
The Other ◽  
Optical Monitoring ◽  
Anionic Polymer ◽  
Aluminium Sulphate ◽  
Shear Rates ◽  
Monitoring Technique ◽  
On Line ◽  
The Mean ◽  
Set Up

The effect of tapered-shear (diminishing velocity gradient) flocculation on the formation, breakage and reformation of flocs using aluminium sulphate and an anionic polymer were evaluated. An on-line continuous optical monitoring technique was used for this purpose. Two different mean shear rates, G=60s−1 and G=100s−1 were tried in the slow stirring stage of the experiments. For the mean G=60 sec−1, sample was stirred at 400 rpm (G=518 sec−1) for 10 seconds then the stirring speed was reduced to 100 rpm (G=60 s−1) and held at this value for the required time (9 minutes). In the other trial, slow stirring speeds of 130 rpm, 100 rpm and 70 rpm and 150 rpm, 100 rpm and 50 rpm for 3 minutes each were used. After slow stirring, the speed increased to 400 rpm (G=518 s−1) for 10 seconds and then reduced back to appropriate slow stirring speed as stated above. A similar approach was applied for mean G=100 s−1. For continuous tests, a laboratory scale set-up was constructed as a tapered flocculation system that consists of three chambers. Flocs formation in the first and third chambers were monitored and compared. Larger flocs that have higher reformation rate were produced with tapered flocculation.

Coagulation monitoring in surface water treatment facilities

1998 ◽  
Vol 38 (3) ◽  
pp. 237-244 ◽  
Author(s):  
Kan Chichuan ◽  
Huang Chihpin
Keyword(s):  
Water Treatment ◽  
Settling Velocity ◽  
Optical Monitoring ◽  
Floc Size ◽  
Surface Water Treatment ◽  
Operation Conditions ◽  
Monitoring Technique ◽  
Coagulation Performance ◽  
Output Ratio ◽  
Treatment Facilities

Coagulant dosing is traditionally determined according to results from jar-tests or operator's experience, which often lead to overdosing or insufficient dosing. In this study, the feasibility of applying an optical monitoring technique to determine chemical dosage and to monitor the coagulation performance in water treatment plants were assessed. To examine the applicability of the monitor under various operation conditions, series of batch trials in the field were conducted to explore the effects of turbidity, pH and rapid mixing intensity on the effectiveness of coagulation. The performance was directly reflected in the output ratio of the monitor, which proved to be an effective index for the floc size and its settling velocity. Therefore, we consider that the optical monitor is an useful instrument in monitoring coagulation in water treatment.

A Simple Optical Monitoring Technique for Determining the Geometrical Characteristics of a Plasma Jet

2006 ◽  
Vol 3 (2) ◽  
pp. 160-164 ◽  
Author(s):  
Boyan E. Djakov ◽  
Dick H. Oliver ◽  
Radomir Enikov ◽  
Elmira Vasileva
Keyword(s):  
Plasma Jet ◽  
Optical Monitoring ◽  
Geometrical Characteristics ◽  
Monitoring Technique

Microtomy of spherical Al2O3 powders

1983 ◽  
Vol 41 ◽  
pp. 74-75
Author(s):  
E.J. Jenkins ◽  
D.S. Tucker ◽  
J.J. Hren
Keyword(s):  
Thin Film ◽  
Size Range ◽  
Particle Aggregation ◽  
Ion Milling ◽  
Thin Sections ◽  
Α Phase ◽  
Convenient Means ◽  
Van Der Waals Attraction ◽  
Negative Feature ◽  
Film Substrate

The size range of mineral and ceramic particles of one to a few microns is awkward to prepare for examination by TEM. Electrons can be transmitted through smaller particles directly and larger particles can be thinned by crushing and dispersion onto a substrate or by embedding in a film followed by ion milling. Attempts at dispersion onto a thin film substrate often result in particle aggregation by van der Waals attraction. In the present work we studied 1-10 μm diameter Al2O3 spheres which were transformed from the amprphous state to the stable α phase.After the appropriate heat treatment, the spherical powders were embedded in as high a density as practicable in a hard EPON, and then microtomed into thin sections. There are several advantages to this method. Obviously, this is a rapid and convenient means to study the microstructure of serial slices. EDS, ELS, and diffraction studies are also considerably more informative. Furthermore, confidence in sampling reliability is considerably enhanced. The major negative feature is some distortion of the microstructure inherent to the microtoming operation; however, this appears to have been surprisingly small. The details of the method and some typical results follow.

Transmission electron microscope studies in special ceramics

1978 ◽  
Vol 36 (1) ◽  
pp. 268-269
Author(s):  
A. Zangvil ◽  
L.J. Gauckler ◽  
G. Schneider ◽  
M. Rühle
Keyword(s):  
Phase Diagrams ◽  
Crystal Structures ◽  
Thin Foil ◽  
Limited Extent ◽  
Complex Materials ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Lattice Resolution

The use of high temperature special ceramics which are usually complex materials based on oxides, nitrides, carbides and borides of silicon and aluminum, is critically dependent on their thermomechanical and other physical properties. The investigations of the phase diagrams, crystal structures and microstructural features are essential for better understanding of the macro-properties. Phase diagrams and crystal structures have been studied mainly by X-ray diffraction (XRD). Transmission electron microscopy (TEM) has contributed to this field to a very limited extent; it has been used more extensively in the study of microstructure, phase transformations and lattice defects. Often only TEM can give solutions to numerous problems in the above fields, since the various phases exist in extremely fine grains and subgrain structures; single crystals of appreciable size are often not available. Examples with some of our experimental results from two multicomponent systems are presented here. The standard ion thinning technique was used for the preparation of thin foil samples, which were then investigated with JEOL 200A and Siemens ELMISKOP 102 (for the lattice resolution work) electron microscopes.

FT-IR microspectroscopic analysis of diseased white matter brain tissues

1995 ◽  
Vol 53 ◽  
pp. 968-969
Author(s):  
Steven M. Le Vine ◽  
David L. Wetzel
Keyword(s):  
White Matter ◽  
Gray Matter ◽  
Twitcher Mouse ◽  
Grid Pattern ◽  
Marked Contrast ◽  
Spatially Resolved ◽  
Ft Ir ◽  
Ir Microspectroscopy ◽  
Chemical Evidence

In situ FT-IR microspectroscopy has allowed spatially resolved interrogation of different parts of brain tissue. In previous work the spectrrscopic features of normal barin tissue were characterized. The white matter, gray matter and basal ganglia were mapped from appropriate peak area measurements from spectra obtained in a grid pattern. Bands prevalent in white matter were mostly associated with the lipid. These included 2927 and 1469 cm-1 due to CH2 as well as carbonyl at 1740 cm-1. Also 1235 and 1085 cm-1 due to phospholipid and galactocerebroside, respectively (Figs 1and2). Localized chemical changes in the white matter as a result of white matter diseases have been studied. This involved the documentation of localized chemical evidence of demyelination in shiverer mice in which the spectra of white matter lacked the marked contrast between it and gray matter exhibited in the white matter of normal mice (Fig. 3).The twitcher mouse, a model of Krabbe’s desease, was also studied. The purpose in this case was to look for a localized build-up of psychosine in the white matter caused by deficiencies in the enzyme responsible for its breakdown under normal conditions.

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