Design Sewer & Physical & Biological Waste Water Treatment
Design Sewer & Physical & Biological Waste Water Treatment
Design Sewer & Physical & Biological Waste Water Treatment
WATER ENGINEERING
MAHYUN AB WAHAB
SCHOOL OF ENVIRONMENTAL
ENGINEERING
UNIVERSITI MALAYSIA PERLIS
TODAYS OBJECTIVE
CO3:
Ability to DEFINE, DESCRIBE,
DESIGN and EXPLAIN basic
structure involved in physical
and biological unit process
applied in wastewater
treatment in Malaysia
30 minutes ASSIGNMENT
One sewerage with 225mm
diameter put at 1:200 slope.
Calculate high and sewage
velocity if its flowrate is
432m3/day. Assume n = 0.013
Please comment
Introduction
Why we treat sewage or wastewater?
Standard A
<20 ?
city
Wastewater
Treatment
Plant
BOD5 = 280mg/l
SS = 360 mg/l
<50?
river
Degree of discharge
Discharge by settlement
EXAMPLE for normal composition of sewage
Organic and inorganic
Organic
solid
(1)
Inorganic
(mineral)
(2)
Total
Organic
(1+2)
BOD5
Settlement
suspended solid
39
15
54
19
Non settlement
Suspended solid
26
10
36
23
90
42
160
12
TOTAL
Dissolved solid
80
80
Table 1 :Example of one sewage sample (all unit in mg/l), Bache, 1989
Example
BOD 280
SS 360
BOD 20
SS 50
Primary
treatment
*BOD 150
*SS 144
Secondary
treatment
Example
TYPE OF TREATMENT
General
A few technique to treat sewerage depend on type of
sewerage.
Optional treatment
Physical
Chemical
Biology
screensing
Precipitation
Activated sludge
Mixing
Disinfection
Rotating Biological
Contractors (RBC)
Flocculation
Absorption
Aerated lagoon
Sedimentation
Neutralization
Trickling Filter
Floatation
Oxidation
Filtration
Settling
Cont
Conventional
Normally we just apply physical and biological
treatment for municipal sewerage
When we use chemical treatment?
type of treatment can classified as below
Pre-treatment
First stage in treat sewerage
Physical treatment and one of the primary treatment
Objective : protect incoming treatment from course object
such as wood, rock, metal and etc.
Example : screens, communitor, grit chamber,
sedimentation tank
Cont
Primary treatment
Refer to pre-treatment process and primary
sedimentation tank
Objective : remove suspended solid from
wastewater, so that biological plant will not over
loaded.
Main function : remove big portion of suspended
solid from wastewater and a few of BOD5
Wastewater volume in primary treatment have to
control. Not too slow and too fast. WHY?
Effluent from primary sedimentation tank are called
sludge
Cont
Secondary treatment
Refer to biological plant
Objective : remove organic biodegradable and suspended
solid that cannot remove in primary treatment
Sludge treatment
Beside primary sedimentation tank, sludge also can find in
secondary sedimentation tank (after biological plant)
Its mean, output from biological plant have to settle in other
tank, commonly called as secondary sedimentation tank.
Sludge also can perform in other process such as septic tank,
Imhoff tank and oxidation pond.
Cont
Tertiary treatment
Advanced treatment
Done when high standard of wastewater
required
Its also done when we want to remove specific
parameter such as nitrogen and phosphorus
Normally include absorption, reverse osmosis
and etc.
Cont
Practically, not all phase or type of
treatment are use
Its engineer responsibility to decide which
unit suitable for the wastewater they have
to treat.
For example,
influent
screens
Primary
Sedimentation
tank
Aerated lagoon
Activated
sludge
Secondary
Sedimentation
tank
effluent
Preliminary
Treatment
Primary
Treatment
Secondary
Treatment
Tertiary Treatment
screensing
sedimentation
Activated
sludge
filtration
grit removal
floatation
biofiltration
disinfection
sedimentation
tertiary ponds
Biological
treatment to
Remove
organic and
Suspended
solids
biological and
chemical treatment
to remove nutrients
and pathogens
grease tank
pre-aeration
flow
measurem
ent
flow balancing
removal of
rags,
rubbish,
grit, oil,
grease
removal of
settleable and
Floatable
materials
effluent
discharge
Primary treatment
Screens
Objective : remove course object to avoid
problem in the next unit treatment
First unit in wastewater treatment unit series
2 type of screens
Mechanical screens
Manual screens
2 type of screens
Course screens
Fine screens
Cont
Manual screens
Mechanical screens
Manual screens
Cont
Parameter
Design criteria
Manually raked
Mechanical raked
Qpeak = ?
Qpeak = ?
25mm
25mm
Slope to vertical
0-45
0-45
1.0m/s
1.0m/s
1.0m/s
1.0m/s
Min. freeboard
150mm
150mm
30m3/106 m3
See figure
7 days
7 days
Screens thickness
25mm
N/A
No
Yes
Flowrate, Q
Cont
After we know a few design criteria, so, width of
screens chamber can determine by this formula
(B S )
F
W
X
S
VD
Where,
Cont
Screens output quantity based on sewage
age and clear spacing.
Sewage volume is between 1.3x10-6 to
3.67x10-5per m3 flowrate with average value
is 1.5x10-5m3/m3 flowrate (Mc Ghee, 1991)
Example
One wastewater treatment plan are planned to
cater 50,000 people. Determine width of screens
chamber and appropriate number of screens
thickness, based on these design criteria:
People, P = 50000
Maximum clear spacing = 25mm
Screens thickness = 10mm
q = standard water consumption for Malaysia
Qpeak = 4.7 p-0.11 DWF
Volume = 0.9m/s
Depth = 0.85m
B=
S=
V=
D=
QPEAK
DWF
10
mm
25
mm
0.9
m/s
0.85
m
= 4.7 p-0.11 DWF
=
qP
11250 m3/day
Q peak =
0.01
0.025
34384.577 m3/day
0.39797 m3/s
W=
W=
W=
W is taken as
(B+S)
S
1.4
0.73
0.8
22.8571
23
pieces
(B+S)*(no. of B)
0.805 m
F
VD
0.5202
m
m
Comminutor
Cont
Another primary unit operation like screens
However, its not function as a screens but as a
grinder. Grind course thing to smaller size and
discharge
Comminutor will not effect the rest of operation
with their output
But, its still have their disadvantage.
Comminutor will increase load for next
operation (especially biological operation)
Grit Removal
Grit is a inorganic material such as
.and..and..
etc
Grit will damage pumps by abrasion and
cause serious operation difficulties in
sedimentation tanks and sludge
digesters by accumulation around and
plugging of outlets and pump suctions
Cont
Grit remover is one of the most important part in
combined sewerage system.
Can u think what are the principle using in grit
chamber?
A lots of different types of grit chamber, such as :
Grit chamber
Gravity Channel
Aerated Grit Channels
Vortex Grit Traps
Detritor
Cont
Every grit removal have different design
approach
It is common practice to remove this
material by grit chambers .
So that, we will only learn how to design grit
chamber.
Cont
Parameter
Design characteristics
Flowrate, Q
Qpeak = ?
1 minutes
<1000
Type
Horizontal flowrate or
vortex
0.2
0.03
Design principle
Flowrate, Q
Using Qpeak = .
Retention Time, t
t = volume / flowrate
Surface Load Rate (SLR)
SLR = Q / As
Cont
Horizontal velocity, Vh
Vh is a horizontal velocity enter
the tank
You must know how to
differentiate between vertical
velocity and horizontal velocity
Vertical velocity occur because
of gravity
Vh
Cont
We know that,
V
t
Q
(3.1)
Q
SLR
As
(3.2)
Cont
Its 2 option when we want to design
grit chamber
Starting from retention time, t
Starting from Surface Load Rate,
(SLR)
Example
One grit chamber is designed for a domestic
wastewater treatment plant. This plant
receives waste from 8000 people. If Qpeak is
used in this design, calculate length, width
and depth of this chamber. Given, SLR is
1500 m3/m2 and horizontal velocity is 25
cm/s.
SOLUTION
Qpeak = 4.7 p-011 DWF
SLR = 1,500 m3 /m2 .day
Vh = 25 cm/s
Width (W) _ ?
Length (L) _ ?
Depth (d) _ ?
DWF
= q*P
= (0.225 m3/cap.day) (8000)
= .m3/day
= 3.739 (1800)
= 6730 m3/day
= 1,500 m3/m2.hari
= 6730/As = 1,500 m3 /m. hari
As
= 4.487m2
Assume depth, d = 1 m; So,
Volume, V
= As (d)
= 4.487 (1)
= 4.487 m3
Retention Time, t
= V/Q
= (4.487 m3)/(6,730 m3/day)
= ..day
= (6.67 x 10-4 day) (24 x 3600 second)
= .. second,
Given Vh
= 25 sm/s
Vh
= L/t
(Horizontal velocity = Length/time taken)
25
= L/57.6
L
= (25 sm/s) * (57.6 s)
= 1,440 sm
= 14.4 m
= .m
As = BL
4.186 m2 = B (14.5)
L = .. m
B
= 0.288 m
d =.. m
Take B as = m
We have assume depth, d =1.0m
Conclusion
L = .m ; B = . m ; d =.m
B = .. m
Grease tank
Grease tank is one of the pre-treatment unit
designed to remove greasy material and lighter
than water.
Some of wastewater consist high composition of
fat, grease and oil. Example, wastewater from
.
So that, we have to remove this greasy material
before its enter next unit operation.
But, grease tank is very rare in domestic
wastewater treatment
Equalization tank
Wastewater is held in the equalization tank to
allow solids to begin settling.
Activated sludge from the leveling ponds is mixed
with the wastewater in the equalization tanks to
begin biological digestion of organic contaminants.
The equalization tank also helps to maintain a more
constant flow rate through the treatment plant.
Sedimentation tank
Sedimentation tank function to settle suspended
solid in wastewater or in easy word, sedimentation
tank separate solids from the liquid stream
Sedimentation tank also known as clarifier
Theoretically, purpose of sedimentation tank is to
divide two component, which is :
Sludge (settled suspended solid)
Effluent
Cont
The purpose of the scraper mechanism mounted
inside the tank, is to collect the settled solids for
removal from the tank by pumping
In circular sedimentation tanks the clarifier
mechanism has sludge scrapers attached to a
rotating arm scraping the sludge towards a central
hopper.
In rectangular clarifiers scrapers are carried along
the tank bottom collecting the sludge into a trough
or hopper at the influent end of the tank.
Cont
A few types of primary sedimentation tank
Rectangular Tank
Circular Tank
Upward flow tank
PARAMETER
UNIT
DESIGN CRITERIA
Flowrate
m3/day
Q peak = ?
Hour
1.5-2.0
SLR at Q peak
Circular (<50 diameter and 3.0
m depth)
Rectangular
m3/m2.day
m3/m.day
Horizontal velocity
mm/s
<15
<45
<30
3:1
m
m
m
2.0 3.5
1.5
5.0-9.0
Degree
Cont
Using Retention time
t = V/Q
Example
Volume = 1000 m3
Flowrate = 50000m3/ day
Retention time = ??
Cont
Using SLR = Q / As
SLR = flowrate / area tank surface
= flowrate / b.l
Unit ???
l
b
Horizontal velocity, Vh
Horizontal velocity is a even velocity enter the tank
Cont
Differentiate between Vh and Vo (Settlement
velocity)
Settlement velocity, Vo is a vertical velocity cause
by gravity
Settlement theory stated design sedimentation
tank (Rectangular or Circular Tank) based on
reference particle moving from top of the tank to
base of the tank (from point A to point B)
Design have to be done with Vh and Vo in almost
same magnitude, so that the particle can settle
ideally.
Cont
REMEMBER : depth of tank NOT
influencing particle settlement
Vh = Q / Ah
Where,
Ah = area of cross section
=bxd
d
Ah
Cont
3 settlement cases
If settlement velocity > horizontal velocity
= particle will settle in front of tank
Cont
Cont
Weir overflow rate
Production of sludge
Settled sludge in primary sedimentation tank can be
estimate using this equation
Dry weight =
(kg.day)
%
removal
of
suspended
x
(1DWF) x
suspended
solid
solid
Cont
Sludge is produced by settled suspended solid
Sludge production can be estimated from output
per capita
Rough estimation by Fuaad, 1990 is
0.0014m3/people.day or 50gram/capita.day
In designing sedimentation tank, volume of sludge
storage also needed. 2-5% of sedimentation tank
volume is using as a rough estimation.
Cont
In calculating sludge storage volume,
dislodging frequency has to determine.
If dislodging is done every day, so that
storage volume needed is just one day.
Design approach of sedimentation tank is
similar with design of grit chamber. Its can
be started from SLR or from retention time.
3.
4.
5.
6.
EXAMPLE
One primary sedimentation tank are receiving influence
from one housing area with 100,000 people. Water
consumption is 200 liter/capita.day. If SLR is 30m3/m2.day,
design:
One rectangular primary sedimentation tank
One circular primary tank with slope 7.5. Determine
sludge produced.
Using this design data:
EXAMPLE
One small city consist 15000 person. Design
one upward flow tank to cater this city using
given design criteria:
q = standard
Retention time at maximum flowrate is 2 hours
SLR = 35m3/m2.day
Sludge production = 0.0016m3/person.day
Dislodging frequency = every day
Slope to horizontal 60
Cont
Compare to primary sedimentation tank that has 3
option of tank, in SST, normally we design circular
tank
This SST is very important to specific unit
operation, especially ASP and aerated lagoon.
Without this tank, that two process cannot operate
because sludge produce cannot settle. As a result,
effluent will consist high number of SS
Cont
The sludge that collects in the SST is called
aerated sludge or activated sludge because
it is fully aerated.
Parameter
Retention
time
SLR
WOR
Minimum
depth
Solid Load
Rate @ Qpeak
Flowrate
150-180 m3/m.day
3m
Aerated tank
Return sludge
Secondary
sedimentation
tank
effluent