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.

Properties of flocs produced by water treatment coagulants

2001 ◽  
Vol 44 (10) ◽  
pp. 231-236 ◽  
Author(s):  
J. Gregory ◽  
V. Dupont
Keyword(s):  
Test Procedure ◽  
Dynamic Monitoring ◽  
Optical Technique ◽  
Water And Wastewater Treatment ◽  
Aluminium Sulfate ◽  
Jar Test ◽  
Water And Wastewater ◽  
Clay Suspensions ◽  
Polyaluminium Chloride ◽  
Floc Breakage

Hydrolyzing coagulants are extensively used in water and wastewater treatment, often under conditions where hydroxide precipitation is important, giving “sweep flocculation”. Pre-hydrolyzed coagulants, such as polyaluminium chloride (PACl) are also widely used and have several advantages over traditional additives, such as aluminium sulfate. Their action is usually discussed in terms of cationic species and charge neutralization. However, precipitation may also be important and this aspect has not been considered in detail. The present work has compared the action of alum and three commercial PACl products on model clay suspensions. The conventional jar test procedure has been used, along with measurements of settled floc volume and dynamic monitoring of floc formation and break-up by an optical technique. The latter method gives very useful information on the nature of the flocs produced and their response to different shear conditions. It is clear from the results that the PACl products form larger and stronger flocs than alum. With all coagulants floc breakage appears to be essentially irreversible. Sediment volumes are slightly lower for flocs produced by PACl than by alum, but the value is proportional to the dosage in all cases.

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.

Dynamic testing of water treatment coagulants

2001 ◽  
Vol 1 (4) ◽  
pp. 65-72 ◽  
Author(s):  
J. Gregory ◽  
L. Rossi
Keyword(s):  
Mode Of Action ◽  
Dynamic Testing ◽  
Test Procedure ◽  
Aluminium Sulphate ◽  
Jar Test ◽  
Iron Salts ◽  
Flow Through ◽  
Preliminary Study ◽  
Selection For ◽  
Empirical Approaches

Pre-polymerised inorganic coagulants, such as polyaluminium chloride (PAC) have several advantages over conventional aluminium and iron salts. However, their mode of action is not fully understood and progress in this area has been made largely by empirical approaches. In this preliminary study we have followed the dynamics of flocculation of model clay/humic acid suspensions following the addition of three different coagulants: aluminium sulphate and two commercial PAC products. Experiments were conducted using controlled stirring rates in a modified jar test procedure, in which the formation and break-up of flocs could be monitored continuously by a flow-through optical technique. The results show significant differences in the behaviour of the coagulants and one of the PAC samples gives much larger and stronger flocs. Further experiments along these lines should help to elucidate the mode of action of different forms of coagulant and to aid in their selection for specific applications.

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.

Formation, breakage and re-formation of flocs formed by cationic starch

2013 ◽  
Vol 68 (6) ◽  
pp. 1352-1358 ◽  
Author(s):  
Qintie Lin ◽  
Huanlong Peng ◽  
Qinlu Lin ◽  
Guangcai Yin
Keyword(s):  
Large Scale ◽  
Separation Efficiency ◽  
Test Procedure ◽  
Mixing Conditions ◽  
Cationic Starch ◽  
Jar Test ◽  
Strong Shear ◽  
Alkaline Conditions ◽  
Polymer Flocculant ◽  
Floc Breakage

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.

scholarly journals Use of helical ribbon mixer for measurement of rheological properties of fruit pulps

2013 ◽  
Vol 19 (No. 4) ◽  
pp. 148-153 ◽  
Author(s):  
P. Novotná ◽  
A. Landfeld ◽  
K. Kýhos ◽  
M. Houška ◽  
J. Strohalm
Keyword(s):  
Shear Rate ◽  
Rheological Properties ◽  
Flow Behaviour ◽  
Rotational Rheometer ◽  
Shear Rates ◽  
Coaxial Cylinders ◽  
Helical Ribbon ◽  
Flow Behaviour Index ◽  
Average Shear ◽  
Behaviour Index

Fruit pulps contain fine particles of the flesh of the original fruit that are suspended in the fruit juice. This suspension has a tendency to settling or separation during measurements of its rheological properties in the rotational rheometer with coaxial cylinders (especially if the greater gap is used). In this case the use of a mixer is convenient. The mixer can serve as a tool for measurement of rheological properties and at the same time it can prevent the settling and it is not sensitive to the occurrence of greater particles in the measured fluid. The helical ribbon mixer was used in this work for measurement of five samples of fruit pulp. The mixer was calibrated by the use of Newtonian fluid of known viscosity (honey). The radius of the inner cylinder of hypothetical rotational rheometer was predicted from the assumption that mixer and cylinder exhibit the same torque necessary for the rotation at the same rotational speed. The average shear rate in the mixed pulp was predicted by using the relation valid for power law fluids and rheometer with coaxial cylinders. The radius (where the average shear rate was calculated) was chosen by the requirement that the shear rate would be almost independent of changes in the flow behaviour index valid for measured pulps. Firstly the flow behaviour index was predicted as a slope of torque vs. rotational speed dependence in log-log co-ordinates. It was found that the flow behaviour index varies in the range 0.2–0.3. The radius was predicted from a graph where shear rates for 0.2 and 0.3 are the same. Then the average shear rates were calculated from rotational speeds for individual flow behaviour indexes. Rheological properties measured by using a mixer correspond to those measured with a rotational rheometer with coaxial cylinders satisfactorily only in the case that the creeping flow regime was kept in the mixed fluid. The fruit pulps are strongly non-Newtonian fluids with very low values of the flow behaviour index around 0.2.

scholarly journals THE IMPACT OF THE OXIDISING AGENT TYPE AND COAGULANT TYPE ON THE EFFECTIVENESS OF COAGULATION IN THE REMOVAL OF POLLUTANTS FROM UNDERGROUND WATER WITH AN INCREASED CONTENT OF ORGANIC SUBSTANCES

2016 ◽  
Vol 24 (1) ◽  
pp. 70-78 ◽  
Author(s):  
Izabela KRUPIŃSKA
Keyword(s):  
Hydrogen Peroxide ◽  
Underground Water ◽  
Total Iron ◽  
Pollutant Removal ◽  
Organic Substances ◽  
Aluminium Sulphate ◽  
Coagulation Process ◽  
Groundwater Samples ◽  
The Impact ◽  
Polyaluminium Chloride

The article presents the results of studies concerning the impact of the method of Fe(II) ion oxidisation on the effectiveness of coagulation in the removal of pollutants from underground water with an increased content of organic substances (TOC up to 5.338mgC/dm3). In order to oxidise the Fe (II) ions before the coagulation process, the underground water was subjected to aeration, or either potassium manganate (VII) or hydrogen peroxide were dosed in the stoichiometric amount in view of the concentration of Fe (II). The efficiencies of three coagulants were compared: that of aluminium sulphate (VI), polyaluminium chloride (PAX XL-60) and iron (III) sulphate (VI) – PIX-112. Coagulant doses expressed in mgal/dm3 or mgfe/dm3 and changed within the range of 1 to 6 mgal(Fe)/dm3. Volume coagulation was performed in 1-dm3 groundwater samples using 1-minute rapid mix (250 rpm) and 25-minute slow mix (30 rpm) followed by 2-hour sedimentation. It has been proven that the type of oxidising agent and coagulant, as well as their dose, co-determines the effectiveness of the removal of the pollutants. Among the used methods of iron (II) oxidisation, the best effects have been achieved by potassium manganate (VII) with regards to the effects of the reduction of colour, turbidity, concentration of manganese and organic substances, and with regards to the extent of total iron removal, oxidisation with dissolved oxygen was the most effective solution. Hydrogen peroxide was the least useful oxidising agent. Regardless of the oxidising agent the best results in the removal of pollutants in the coagulation process were produced by the coagulant: pre-hydrolysed polyaluminium chloride PAX XL-60, and the worst by the iron coagulant: iron (III) sulphate (VI). Analysis of the results of the studies also showed that the effectiveness of pollutant removal from the underground water in the coagulation process was decreased together with an increase in the value of the TOC/Fetot only in the case of water samples which, after aeration, differed in terms of the coefficient of organic substances and total iron (D). Such a relationship was not found when potassium manganate (VII) and hydrogen peroxide were used for oxidisation before the coagulation process.

Roll cells and disclinations in sheared nematic polymers

2001 ◽  
Vol 449 ◽  
pp. 179-200 ◽  
Author(s):  
J. J. FENG ◽  
J. TAO ◽  
L. G. LEAL
Keyword(s):  
Shear Rate ◽  
Shear Flow ◽  
Simple Shear ◽  
Flow Direction ◽  
Flow Regimes ◽  
Flow Conditions ◽  
Break Up ◽  
Nematic Polymers ◽  
Defect Nucleation

We use the Leslie–Ericksen theory to simulate the shear flow of tumbling nematic polymers. The objectives are to explore the onset and evolution of the roll-cell instability and to uncover the flow scenario leading to the nucleation of disclinations. With increasing shear rate, four flow regimes are observed: stable simple shear, steady roll cells, oscillating roll cells and irregular patterns with disclinations. In the last regime, roll cells break up into an irregular and uctuating pattern of eddies. The director is swept into the flow direction in formations called ‘ridges’, which under favourable flow conditions split to form pairs of ± 1 disclinations with non-singular cores. The four regimes are generally consistent with experimental observations, but the mechanism for defect nucleation remains to be verified by more detailed measurements.

Measurement of the average shear rate around a microparticle in the shear thinning medium with laser tweezers

2017 ◽  
Vol 36 (5) ◽  
pp. 529-533
Author(s):  
Piotr Domagalski ◽  
Marek Dziubinski ◽  
Ryszard Pawlak ◽  
Mariusz Tomczyk
Keyword(s):  
Shear Rate ◽  
Shear Thinning ◽  
Laser Tweezers ◽  
Average Shear Rate ◽  
Average Shear

Magnesium Induced Algal Flocculation in a Fluidized Bed

1991 ◽  
Vol 23 (7-9) ◽  
pp. 1695-1702 ◽  
Author(s):  
S. Elmaleh ◽  
J. Coma ◽  
A. Grasmick ◽  
L. Bourgade
Keyword(s):  
Pressure Drop ◽  
Fluidized Bed ◽  
Suspended Solids ◽  
Energy Requirement ◽  
Test Procedure ◽  
Total Suspended Solids ◽  
Oxidation Pond ◽  
Waste Sludge ◽  
Jar Test ◽  
Solids Separation

The effectiveness of the use of seawater and of magnesium in the removal of microalgae from oxidation pond effluents was investigated using the jar test procedure. The results indicated that the major flocculating reaction is the magnesium hydroxide precipitation at pH 11.5. The next step was to intensify the liquid-solids separation by use of a fluidized bed flocculator packed with 800 µm inert resin particles provided with an inclined multitubular settler. The total suspended solids abatement could reach 95 % with a superficial upflow velocity of 30 m/h corresponding to a residence time through the whole unit of 5 minutes only. The energy requirement quantified by the pressure drop through the bed is very low. Besides, the waste sludge extracted from the settler is easily thickened.

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