water treatment technology (tas 3010) lecture notes 9c - sedimentation
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WATER TREATMENT TECHNOLOGY (TAS 3010) LECTURE NOTESUNIVERSITY MALAYSIA TERENGGANU 2009Disclaimer: I don't own this file. If you believe you do, and you don't want it to be published here, please let me know. I will remove it immediatelyTRANSCRIPT
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
© SHAHRUL ISMAIL, DESc.University College of Science and Technology Malaysia
CHAPTER 3:Environmental Microbiology
CHAPTER 9c : CHAPTER 9c : CHAPTER 9c : CHAPTER 9c :
TAS 3101 : WATER TREATMENT TECHNOLOGY
Water Water
Treatment Treatment
Process :Process :
SedimentationSedimentation
Water Water
Treatment Treatment
Process :Process :
SedimentationSedimentation
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Menu
1) Introduction
2) Settling Types
3) Settling Velocity
4) Design Calculation
5) Analysis
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Process of heavier solid particles in suspension, settle to the body
of the tank by gravity
Designed to remove settled water from the basin without carrying
away any of the floc particles.
Depends on :
i) Velocity of flow
ii) Size and shape of particles
iii) Viscosity of water
Sedimentation - Intro
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Type of particles :
1) Discrete / individual particle
- Size, velocity constant during the settling
- Density 2,000 – 2,200 kg/m3
2) Flocculant particles
- Size, velocity fluctuates during the settling
- Particles flocculate and grow bigger in size
- Density 1,030 – 1,070 kg/m3
Sedimentation – Particle Type
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
In ideal reactors, average velocity of water equal to its flow rate divided by
the area through which it flows,
v = Q (Eq. 1)
Ac
Where,
V = water velocity (m/s)
Q = water flow (m3/s)
Ac = cross surface area (m2)
Sedimentation - Concepts
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
- Settling velocity (Vs) must be determined to assure ideal sedimentation tank.
- Overflow rate (Vo) must be set at some value LESS THAN or EQUAL to Vs
- Vo = Q = H
As t
Where
Q = flow rate
As = surface area
H = depth of water
t = detention time
Settling Velocity
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
- Settling velocity is different for different types of particles.
- If Vs > Vo : Particles completely settled
If Vs < Vo : Particles do not settle unless particles at h level when
entering the sedimentation tank, where ;
h = Vs t
- Effective sedimentation tank : Vo < Vs
- Achieved by increasing the area of the tank (Vs = Q/As)
Settling Velocity
W
pWS
dGsgV
18
)997.0( 2
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Settling Velocity
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Three classes of particles settling :
Type 1
i) Particles settle discretely at a constant velocity
ii) Settle as individual particles and do not flocculate.
iii) E.g. : Sand, grit material
iv) Occurs during :
i) Presedimentation for sand removal
ii) Grit chamber
iii) Settling of sand during rapid sand filter cleaning
v) Concentration : very low
Settling Types
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Type 2
i) Flocculate during sedimentation
ii) Size constantly changing
iii) Settling velocity is changing
iv) Settling velocity increase with depth and extent of flocculation.
v) Occurs during :
i) Alum or iron coagulation
ii) Primary Sedimentation basins
iii) Settling tanks in trickling filtration
vi) Concentration : low
Settling Types
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Type 3 or Zone
i) Settle as mass and form a layer – “blanket
ii) Concentration high (greater than 1000 mg/L)
iii) Distinct clear zone and sludge zone are present.
iv) Occurs during :
i) Lime-softening sedimentation
ii) Activated sludge sedimentation
iii) Sludge thickeners
Settling Types
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
- Reduce the turbulence caused by rushing water leaves the
tank.
- Series of troughs, called “weirs” are put in place – feed into
central channel or pipe for transport of the settled water.
- Purpose :
i) Provide large area for the water flow to flow through.
ii) Minimize the velocity in the sedimentation tank near
outlet zone.
Sedimentation - Weirs
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Weir arrangement - Rectangular
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Weir arrangement - Circular
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Basic design calculation :
1) Tank Volume
2) Detention Time
3) Surface Overflow Rate
4) Mean Flow Velocity
5) Percent Settled Biosolids
6) Particle Settling
7) Overflow rate
Sedimentation - Calculation
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Determine criteria of the particles and the effectiveness of the tank
Method :
i. Use settle column : Depth of water is as same as actual water depth
ii. In steady state
iii. Record :
a) Initial concentration of the suspended solid, express as Co
b) Withdrawn sample at every sample ports, at selected time
intervals, Ct
iv. Calculate :
Percent removal, % R for every sample point and sampling time
% R = Co – Ct
Co
v. Graf : Plot % R at depth versus time
Sedimentation - Analysis
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
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