WATER TREATMENT
Sedimentation
WATER TREATMENT
100
cumulative frequency distribution [%]
100 time [s]
suspended solids content [%] 600
80
80 900
1200
60 1800
60
2700
3600
40 40
h= 0.75 m 5400
7200
h= 1.5 m
20 20
h= 2.25 m
h= 3.0 m
0
0
0 1 2 3 4 5 0 0.5 1 1.5 2 2.5 3
h/t [m/h] distance under water surface [m]
trap t=0 t=$ t = 2$
1
tube
2
3 constant
water temperature
4
sample of
the solution
5
silt
,sedimentation water treatment
Framework
This module represents sedimentation.
Contents
This module has the following contents:
1. Introduction
2. Theory
2.1 Sedimentation of discrete particles
2.2 Horizontal flow settling tanks in practice
2.3 Settling efficiency of a suspension
3. Influences on settling in a horizontal flow tank
3.1 Influence of turbulence
3.2 Influence of stability
3.3 Influence of bottom scour
3.3 Influence of flocculant settling
4. Practice
4.1 Determination of the dimensions of an ideal settling tank
4.2 Inlet constructions
4.3 Outlet constructions
5. Settling tank alternatives
5.1 Vertical flow settling tank
5.2 Floc blanket clarifier
5.3 Tray settling tanks
5.4 Tilted plate settling
52
, water treatment sedimentation
1 Introduction
Q Q
V0 B
Sedimentation is a treatment process in which
suspended particles, like flocs, sand and clay are inlet sedimentation zone L outlet
zone zone
re-moved from the water.
Sedimentation can take place naturally in reser- Q Q
V0 H
voirs or in compact settling installations. slib zone
Examples of settling installations are the horizon-
tal flow settling tanks, the tilted plate settlers and Figure 2 - Horizontal flow settling tank
the floc blanket installations.
Sedimentation occurs because of the difference
Sedimentation is frequently used in surface water in density between suspended particles and wa-
treatment to avoid rapid clogging of sand filters ter.
after coagulation and floc formation (Figure 1). The following factors influence the sedimentation
Sedimentation is applied in groundwater treat- process: density and size of suspended particles,
ment installations for backwash water treatment. water temperature, turbulence, stability of flow,
bottom scour and flocculation:
In horizontal flow settling tanks (Figure 2) water - density the greater the density of the par-
is uniformly distributed over the cross-sectional ticles, the faster the particles set-
area of the tank in the inlet zone. tle
A stable, non-turbulent, flow in the settling zone - size the larger the particles are, the
takes care of the settling of suspended matter in faster they settle
the settling zone. - temperature the lower the temperature of the
The sludge accumulates on the bottom or is con- water is, the higher the viscosity,
tinuously removed. so the slower the particles settle
In the outlet zone the settled sludge must be pre- - turbulence the more turbulent the flow is, the
vented from being re-suspended and washed out slower the particles settle
with the effluent. - stability instability can result in a short-cir-
cuit flow, influencing the settling
of particles
Reservoir - bottom scour during bottom scour, settled
Fe (III) particles are re-suspended and
Floc formation washed out with the effluent
- flocculation flocculation results in larger parti-
Floc removal by sedimentation cles, increasing the settling veloc-
ity.
Ozonation
Filtration
2 Theory
Activated carbon filtration
Cl2/ClO2 2.1 Sedimentation of discrete particles
Clear water reservoir Discrete particles do not change their size, shape
or weight during the settling process (and thus do
not form aggregates).
Figure 1 - Process scheme of a surface water treat- A discrete particle in a fluid will settle under the
ment plant influence of gravity. The particle will accelerate
53
Sedimentation
WATER TREATMENT
100
cumulative frequency distribution [%]
100 time [s]
suspended solids content [%] 600
80
80 900
1200
60 1800
60
2700
3600
40 40
h= 0.75 m 5400
7200
h= 1.5 m
20 20
h= 2.25 m
h= 3.0 m
0
0
0 1 2 3 4 5 0 0.5 1 1.5 2 2.5 3
h/t [m/h] distance under water surface [m]
trap t=0 t=$ t = 2$
1
tube
2
3 constant
water temperature
4
sample of
the solution
5
silt
,sedimentation water treatment
Framework
This module represents sedimentation.
Contents
This module has the following contents:
1. Introduction
2. Theory
2.1 Sedimentation of discrete particles
2.2 Horizontal flow settling tanks in practice
2.3 Settling efficiency of a suspension
3. Influences on settling in a horizontal flow tank
3.1 Influence of turbulence
3.2 Influence of stability
3.3 Influence of bottom scour
3.3 Influence of flocculant settling
4. Practice
4.1 Determination of the dimensions of an ideal settling tank
4.2 Inlet constructions
4.3 Outlet constructions
5. Settling tank alternatives
5.1 Vertical flow settling tank
5.2 Floc blanket clarifier
5.3 Tray settling tanks
5.4 Tilted plate settling
52
, water treatment sedimentation
1 Introduction
Q Q
V0 B
Sedimentation is a treatment process in which
suspended particles, like flocs, sand and clay are inlet sedimentation zone L outlet
zone zone
re-moved from the water.
Sedimentation can take place naturally in reser- Q Q
V0 H
voirs or in compact settling installations. slib zone
Examples of settling installations are the horizon-
tal flow settling tanks, the tilted plate settlers and Figure 2 - Horizontal flow settling tank
the floc blanket installations.
Sedimentation occurs because of the difference
Sedimentation is frequently used in surface water in density between suspended particles and wa-
treatment to avoid rapid clogging of sand filters ter.
after coagulation and floc formation (Figure 1). The following factors influence the sedimentation
Sedimentation is applied in groundwater treat- process: density and size of suspended particles,
ment installations for backwash water treatment. water temperature, turbulence, stability of flow,
bottom scour and flocculation:
In horizontal flow settling tanks (Figure 2) water - density the greater the density of the par-
is uniformly distributed over the cross-sectional ticles, the faster the particles set-
area of the tank in the inlet zone. tle
A stable, non-turbulent, flow in the settling zone - size the larger the particles are, the
takes care of the settling of suspended matter in faster they settle
the settling zone. - temperature the lower the temperature of the
The sludge accumulates on the bottom or is con- water is, the higher the viscosity,
tinuously removed. so the slower the particles settle
In the outlet zone the settled sludge must be pre- - turbulence the more turbulent the flow is, the
vented from being re-suspended and washed out slower the particles settle
with the effluent. - stability instability can result in a short-cir-
cuit flow, influencing the settling
of particles
Reservoir - bottom scour during bottom scour, settled
Fe (III) particles are re-suspended and
Floc formation washed out with the effluent
- flocculation flocculation results in larger parti-
Floc removal by sedimentation cles, increasing the settling veloc-
ity.
Ozonation
Filtration
2 Theory
Activated carbon filtration
Cl2/ClO2 2.1 Sedimentation of discrete particles
Clear water reservoir Discrete particles do not change their size, shape
or weight during the settling process (and thus do
not form aggregates).
Figure 1 - Process scheme of a surface water treat- A discrete particle in a fluid will settle under the
ment plant influence of gravity. The particle will accelerate
53
