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Group-3

Smarika Kulshreshtha

Sanjeeb Mohapatra

Harshad Arote

Ashutosh

G-Force in CoagulationFlocculation Systems and its

significance

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Rapid Mixing and Flocculation

Rapid mixing is used to:

Disperse chemicals uniformly throughout the mixing

basin

Allow adequate contact between the coagulant and

particles

Microflocs are produced

Flocculation is used to:

Agglomerate microflocs to larger ones

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Devices

Agitation in rapid mixing and flocculation isperformed by:

Mechanical agitators (most common)

Pneumatic agitators

Baffled basins

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Design

The degree of mixing is based on the powerprovided, which is measured by the velocity

gradient:

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Velocity Gradient, G

The velocity gradient of two fluid particles : 0.05ft apart

relative velocity : 0.2fps

2fps/0.05ft = 40fps/ft d

V

1

V

2

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Detention Time

For rapid mixing basins

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Flocculation Complete flocculation depends on:

The relative ease and rate of microflocs

aggregation

Number of particle collisions by gentle & prolonged

agitation agglomeration of floc. Floc Characteristics governed by G

High G ; large floc will not form; high shear forces

The rate of particle collision G

Shear force G Total number of particle collisions GT

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Effect of G & T over Floc

formation

G T Floc Characteristics

Large Small Small and dense

Small Large Larger and lighter

Largerand dense Floc are the main characteristics of goo

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Influence of velocity gradient and rapid mixing time on

flocs formed by Polysilica Iron (PSI) and PolyAluminum

chloride (PACl)

The aim of this study : to investigate

the effect of different velocity gradients and rapid

mixing times on the formation, breakage, and regrowth of

kaolin flocs formed by PSI and PACl.

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Materials and Methods

Preparation of Kaolin suspension

Kaolin clay was used as the model suspension

Coagulants agents

Polyaluminum chloride (PACl) and

Polysilicates Iron (PSI)

Coagulants and rapid mixing

Jar test

3 min of rapid mixing at 150 rpm

Flocc. period : 30 min at 30 rpm & settling period : 60 min

Floc size

Particle Size Analyser Floc strength and Recovery factors

Zeta potential measurements

Micro-Electrophoresis Apparatus

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Effect of velocity gradient on the floc property of kaolin system:

The floc size

Growth region low-velocity gradient G

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Effect ofrapid mixing time on the floc property of kaolin system

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Jr-Lin Lin, Jill R. Pan, Chihpin Huang

Enhanced particle destabilization andaggregation by flash-mixing

coagulation for drinking water treatment

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OBJECTIVE

Investigation of enhanced rapid mixing intensityon the performance of coagulation for natural

turbid water treatment.

Two surface water samples:

Low and High Turbidity

PACl

G values: (200-800 s-1)

Pilot scale in line IFM

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Materials and Methods

Water samples from WTP Fengyuan, Taiwan 200 NTU (HT)

15 NTU (LT)

Commercial PACl ( 10% Al2

O3

)

Inductively Coupled Plasma Atomic Emission

Spectometry

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Experiments

Standard Jar Tests (Optimal CoagulationDosage)

Rapid Mixing ;100-300 rpm (G=200-800 s-1); 15 sec

(WTP simulation)

Slow Mixing ; 30 rpm (G=25s-1) ; 10 min

Turbidity, DOC, Zeta Potential

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1.75 mg/L (LT)

2mg/L (HT)

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Mixing Test Mechanical Mixing

G values: (200-800 s-1)

IFM (PFR)

(G > 5000 s-1 )

554 NTU, 271 NTU, 98 NTU

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References

1. T. S. Aktas, M. Fujibayashi, C. Maruo, M.Nomura & O. Nishimura, Influence of velocitygradient and rapid mixing time on flocs formedby polysilica iron (PSI) and polyaluminium

chloride (PACl), Desalination and WaterTreatment (2013),51:22-24, 4729-4735.

2. Jr-Lin Lin, J. R. Pan, C. Huang, Enhancedparticle destabilization and aggregation byflash-mixing coagulation for drinking water

treatment, Separation and PurificationTechnology, 115 (2013) 145-151

3. H. S. Peavy, D. R. Rowe, G. Tchbanoglous,Environmental engineering, McGraw-Hill, 1985

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Thank You