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7/30/2019 G-Force in Coagulation Flocculation Systems
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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