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 9 : CHAPTER 9 : CHAPTER 9 : CHAPTER 9 :
TAS 3101 : WATER TREATMENT TECHNOLOGY
Water Water
Treatment Treatment
Process :Process :
FlocculationFlocculation
Water Water
Treatment Treatment
Process :Process :
FlocculationFlocculation
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
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1) Introduction
2) Flocculation Theory
3) Flocculation Factors
4) Velocity Gradient
5) Flocculation Types
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Introduction
- Slow
- Slow mixing process in which particles are brought into contact in
order to promote their agglomeration.
- Conversion factors simplify changing from one unit of measurement to
another.
- There are two conditions under which water is measured—water at
rest and water in motion. Water at rest is measured in units of volume.
Water in motion is measured in units of flow— unit of volume for a
convenient time unit. It is important that the difference between a unit of
volume and a unit of flow be kept in mind.
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Agglomeration of destabilized particles into microfloc – second stage of floc growth
Floc : Bulky floccules which can be settled
Flocculant / Flocculant aid : Addition of another reagent promote the formation of the floc.
Relies on turbulence
Accomplished by gentle stirring
Enhance sedimentation
Flocculation
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Flocculation
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Flocculation Theory
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Factors affecting performance of flocculation process
1) pH
i. Prominent factor
ii. Optimum pH range
iii. The type of colloid
iv. Chemicals to adjust the pH of the water
v. Trial and error testing
Flocculation Factors
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
2) Tank volume
The volume of the tank is calculated using the following formula:
V = Q t
Where:
V = volume
Q = flow
t = detention time
Flocculation Factors – Con’d
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
3) Detention time
Time required for a small amount of water to pass through a tank at a given flow rate. Mathematically, detention time is given by the following formula:
t = V Q
Where:
t = detention time
V = tank volume
Q = flow
Flocculation Factors – Con’d
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Velocity Gradient
The velocity of water flowing through the flocculation basin must be within a
very specific range, designed to gently mix the water without breaking apart
the floc.
Measurement of the intensity of mixing in the chamber.
Determines how much the water is agitated in the tank,
Determines how much energy is used to operate the flocculator.
Where
G = Velocity gradient
P = Power input
u = dynamic viscocity
V = Volume
Velocity Gradient
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
- Design parameter for flocculation is Gt (dimensionless
number)
- Where;
G = velocity gradient, s-1 (20 – 75 s-1)
t = time, s (10 – 60 min)
Gt = 12 000 – 270 000 (unitless)
- High G values with Low t : Small and Dense flocs
- Low G values with High t : Larger and Lighter flocs
Velocity Gradient
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
- Vary from cylindrical to rectangular or cubical.
- Mixed simply by water flowing around baffles, or with a variety of
types of paddles, turbines, and propellers.
Vertical-shaft, turbine-type impeller Horizontal-shaft
paddle
Flocculation - Mixers
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Baffled Chamber Flocculator
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Flocculation - Types
TYPESTYPES
MECHANICAL MECHANICAL DEVICESDEVICES
HYDRAULIC HYDRAULIC METHODSMETHODS
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
1) MECHANICAL DEVICES
- Most often in small plants
Advantages :
i) Prevents water from rotating continuously in the same direction
around the shaft
ii) Low head loss
Disadvantages :
i) Low velocity around the shaft
ii) High operation and maintenance cost
Mechanical Devices
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
DESIGN DETAIL - POWER
Power = Force x Velocity
P = FD x Vp
Where;
P = power input, Watt or Nm/s
FD = drag force on paddles, N
Vp = velocity of paddles (velocity relative to the water), m/s
Mechanical Design - Power
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
DESIGN DETAIL - FORCE
FD = ½ CD Ap Vp2 p
Where;
CD = coefficient of drag, 1.8 for flat blades
Ap = area of paddle blades, m2
p = density of water, kg/m3 ( 998.2 kg/m3)
Mechanical Design - Force
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
DESIGN DETAIL – POWER
P = G2 µ
Where;
G = velocity gradient, s-1
µ = dynamic viscocity, Ns/m2
= volume of mixing tank, m3
P = power input, Watt or Nm/s
THEREFORE;
Overall Equation :
P = CD AP (Vp)3 p
2
Mechanical Design - Power
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Measure of the reduction in the total head (sum of elevation head,
velocity head and pressure head) of the fluid as it moves through a
fluid system
Present :
i. Friction between the fluid and the walls of the pipe; the
ii. Friction between adjacent fluid particles as they move
relative to one another;
iii. Turbulence caused whenever the flow is redirect or
affected
Proportional to the length of pipe, the square of the fluid velocity
Head Loss
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Resistance of water to flow due to internal
molecular forces.
Related to the liquid's temperature.
Viscosity
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
A mechanical flocculator is used to treat 38000m3/day water with
detention time 20 minutes.
a) Design the dimension of the tank if L : W : d = 1 : 4 : 2
b) Find the power required when velocity gradient is 55s-1 and dynamic
viscosity 1.002 x 10-3 N.s/m2
c) If the tank have 3 paddles and every paddle have 4 plate with
relative velocity of paddles is 0.38 m/s and coefficient drag is 1.8,
find the area of 1 plate.
(Water density = 998.2 kg/m3)
Mechanical - Problems
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Solution :
For a) Use volume tank formula to find each
dimension of L, W, d
For b) Find power, use formula that can fits all the
information given
For c) Use formula Power that fits all the information
given
Mechanical - Problems
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Solution :
a) = Qt
= 38,000 m3/day x 20 mins
= 527.8 m3.
= L x W x d
= 527.8m3 = 8L3
L3 = 527.8 /8
L = 4.04m W = 4 x 4.04 = 16.16m d = 8.08 m
Mechanical - Problems
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Solution :
b) P = G2
=(55)2 (1.002 x 10-3)(527.80) p
= 1599.8 Watt.
c) P = CD Ap (Vp)3 p
2
Ap = 1599.8 (2)
(1.8) (0.38)3 (998.2)
= 32.45 m2 So, area of 1 plate = 2.7 m2
Mechanical - Problems
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
- Baffle types
- Induce required velocity gradients for achieving floc
formation
Advantages :
i) Simple to construct and operate
ii) Less chance of short circuiting
Disadvantages :
i) Cannot be easily adjusted
ii) Increase head loss
Hydraulic Flocculation
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
1. Velocity in the channel : 10 – 30cm/s
2. Width of the channel : 45 cm
3. Depth of flow : > 1.0m
4. Detention time : 10 – 20 minutes
5. Loss of head : 15 – 60 cm
Hydraulic – Design Detail
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
To design;
1) Tank volume,
2) Distance of flow, D
3) Cross Sectional Area between baffle, Ax
4) Depth of channel, d
5) Clear distance between baffle and the end of wall, Y
6) Effective length of each channel, Pe
7) No. of channel required for each compartment
8) Length and width basin, L & W
Hydraulic – Design Detail
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
1) Total volume,
= Q x t
2) Distance of flow, D
D = t x v
3) Cross Sectional Area between baffle, Ax
Ax = / D
4) Depth of channel, d
d = A / Distance between baffles
Hydraulic – Design Formulas
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
5) Clear distance between baffle and the end of wall, Y
Y = 1.5 x Distance between baffles
6) Effective length of each channel, Pe
Pe = Width of each compartment - Y
7) No. of channel required for each compartment,
8) Length and width basin, L & W
Hydraulic – Design Formula
No. of channel for total distance flow = D/ Pe
So, for each compartment = No. of channel/ of total distance flow / total compartments
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
1) Total volume,
= Q x t
= 20 x 106 L/day x 25 min x1 m3/1000L x day/1440 min
= 347 m3
2) Distance of flow, D
D = t x v
= 25min x 0.17 m/s x 60s /1 min
3) Cross Sectional Area between baffle, Ax
Ax = / D
4) Depth of channel, d
d = A / Distance between baffles
Hydraulic – Design Formulas
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
3) Cross Sectional Area between baffle, Ax
Ax = / D
= 347m3 /255 m
= 1.36 m2
4) Depth of channel, d
d = Ax / Distance between baffles
= 1.36 m2 / 0.75 m
= 1.81m
Hydraulic – Design Formulas
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
5) Clear distance between baffle and the end of wall, Y
Y = 1.5 x Distance between baffles
= 1.5 x 0.75
= 1.125 m
6) Effective length of each channel, Pe
Pe = Width of each compartment – Y
= 3m – 1.125m
= 1.875m
7) No. of channel required for each compartment,
8) Length and width basin, L & W
Hydraulic – Design Formula
No. of channel for total distance flow = D/ Pe
So, for each compartment = No. of channel/ of total distance flow / total compartments
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
7) No. of channel required for each compartment,
No. of channel for a total distance of flow = D/Pe
= 255
m/1.875
= 136
channel
No. of channel for EACH compartment = 136 / 3= 45.3
8) Length and width basin, L & W
Hydraulic – Design Formula
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
8) Length and width basin, L & W
Length = (135 x 0.75 m) + ( 135 x 0.075m)
= 111.375m
Width = 1.875 m
Check Volume = 111.375 x 1.875 x 1.81 = 380 m.
Hydraulic – Design Formula
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Design a baffle type basin of round the end type with the
following data :
Daily quantity of water to be treated = 20 MLD
Detention time = 25 min
Average velocity of flow = 0.17 m/s
Distance between baffles = 0.75 m.
Thickness of each baffle = 0.075 m
3 compartment,
Hydraulic – Problems
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
Hydraulic – Problem Solution
1) Calculate the tank volume,
= Qt
= 20 x 106 L/day x 25 min
= 260 m3
2) Distance of flow, D
D = tv
= 25 min x 0.17 m/s
=
Izan Jaafar, Engineering Science, FST, UMTIzan Jaafar, Engineering Science, FST, UMT
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