This document provides an overview of a wastewater treatment course. It begins with an outline of course content including preliminary treatment, primary treatment, secondary treatment, advanced treatment, and sludge treatment. It then discusses why wastewater treatment is important to protect receiving waters and public health. Various unit processes are described at a high level, including wastewater collection systems, preliminary treatment like bar racks and grit removal, primary sedimentation, and secondary biological treatment processes like activated sludge. Key terms are also defined, such as BOD, TSS, and the 30/30 rule for secondary effluent quality.

1. CE 441 - Wastewater Treatment I
Jian Peng, Ph.D. jpeng@fullerton.edu
1

2. Content for WW Treatment
Objective of WW Treatment
WW Collection and Sewers
Overview of WW Treatment
Preliminary Treatment
Primary Treatment
Secondary Treatment
 Activated Sludge Process
 Attached Growth process
 Other Biological Process
Advanced WW Treatment
WW Sludge Treatment
Effluent Disposal
2

3. Why Do We Treat
Wastewater?
Swimable and Fishable!
 To Protect the health of
the receiving water
 Water reuse
 Alternative water
resources
 Aesthetics
 To protect the health of
humans.
3

4. Wastewater
Collection &
Treatment
Storm sewer
Sanitary sewer
 Domestic
 Industrial
Combined sewer
4

5. Sanitary
Sewer
System
Wastewater leaves residences and buildings through
4” and 6” diameter building sewers.
These sewers are owned by the owner to the point of
connection with the publicly owned sewer.
5

6. Sanitary
Sewer
System
Building sewers empty into larger sewer mains.
They then empty the wastewater into trunk sewers.
Wastewater from the trunk sewers empties into
interceptor sewers.
6

7. Sewer
Corrosion
Wastewater turns septic, and H2S is formed.
Crown corrosion (odor & sink hole) problems
Spray of caustic solution; chlorine disinfection; hydrogen
peroxide addition; flushing with NaOH(OCSD)
Biotrickling filter for odor control (LA City)
7
Sewer rehab – a “big” project (e.g. 1400 mi. for LACSD)

8. Manhole and Lift Station – Sewer network
Manhole – provide access to sewer for cleaning,
repair, sampling, and flow measurements.
In some cases, it becomes necessary to pump the
sewage up from a low point to a higher elevation,
either to reach a treatment plant or to reach
another gravity sewer.
8

9. Gravity Sewer System - Example
A gravity sewer system is being designed for a
minimum velocity of 2 ft/sec. What is the reason
behind the practice?
(a) To prevent deposition of solids
(b) To release trapped sewer gases
(c) To ventilate the water with turbulence
(d) TO reduce the length of piping necessary
The answer is (a).
9

10. Hydraulics – Manning
equation
C 2 3 12
V=
R S
n
V = velocity of flow in feet per second (meters per
second)
C = Constant = 1.486 for English units (1.00 for
metric units)
R = Hydraulic Radius in feet (meters)
S = channel slope in ft/ft or m/m
n = Manning roughness coefficient
10

11. Hydraulics Manning equation
1.486 2 3 1 2
V=
R S
n
where v is the velocity in cfs
R is the hydraulic radius (ft)
R=
h
b
Area (A)
Wetted perimeter (Pw)
What is the hydraulic radius of
a full-flow circular pipe with a
radius of r?
R=
bh
b+2h
If b>>h
R~h
11

12. Sanitary Sewer - Example
The average velocity (fps) of a steady uniform flow in
a 15”-diameter sewer line with a slope of 0.35%, a
depth of 3 in, and a Manning’s roughness coefficient
of 0.012 is most nearly:
1.486 2 3 1 2
V=
R S
n
y / d o = 3 / 15 = 0.2; d o = 15in = 1.25ft
From Open Channel Hydraulics (by Chow),
R/d o = 0.1206 → R = 0.1206(1.25) = 0.151
16 = (0.4644 / 0.012)D 8 / 3 (0.002)1 / 2
2
1
1.486
3 (0.0035) 2 = 2.08fps
V=
(0.151)
0.012
12

13. Storm Sewer - Example
A proposed storm sewer system will have a slope of
0.20%. The design flow for the line has been
determined to be 16 cfs. Assume steady, uniform
flow and a Manning’s roughness coefficient of 0.012.
What would be the minimum circular pipe size?
1.486 2 3 1 2
V=
R S
n
1.486 D 2 3 1 2 πD 2
Q = VA = [
( ) S ](
)
n
4
4
8
1
0.4632
3S 2]
=[
( D)
n
16 = (0.4644 / 0.012)D 8 / 3 (0.002)1 / 2
→ D = 2.30ft = 27.65in
13

14. What is Inflow and Infiltration (I&I)?
Uncapped
Cleanout
House
Lateral
Catch Basin
to Sanitary
Cracked or
Broken Pipe
Roof Drain
Connection
Connected
Foundation Drain/
Sump Pump
Faulty Manhole
Cover or Frame
Deteriorated
Manhole
Storm
Sewer
Sanitary
Sewer
Storm CrossConnection
Faulty Lateral
Connection
Inflow is typically rain water that enters publicly owned
sewer and manholes, as well as through private
property sources such as rain leaders, sump pumps,
foundation drains, and leaking house services.
Infiltration is typically the seepage of groundwater into
the sanitary sewer system through cracks or joints of
14
manholes and pipes; and leaking house services.

15. Smoke Testing (for I/I)
Simulated smoke will be injected into the sewer
system. As a result smoke may be seen coming from
manhole covers, storm drains, roof vents, and building
foundations.
After each setup the smoke test will last
approximately 30 minutes.
15

16. Sable: Santa Barbara’s Leaky
Sewer Detector
16

17. Significance of Wastewater Contaminants
Suspended solids – can cause sludge deposits and
anaerobic conditions in the environment
Biodegradable organics – can cause anaerobic
conditions in the environment
Pathogens – transmit disease
Nutrients – can cause eutrophication
Heavy metals – toxicity to biota and humans
Refractory organics – toxicity to biota and humans
Dissolved solids – interfere with reuse
What are removed by a POTW (publicly-owned
treatment works)?
17

18. Typical Composition of Untreated Wastewater
Constituent
Weak (mg/L)
Strong (mg/L)
Alkalinity (as
CaCO3)
BOD5 (as O2)
50
200
100
300
COD (as O2)
TOC (as C)
250
75
1000
300
TSS
100
350
TDS
200
1000
Chloride
30
100
Total Kjeldahl
Nitrogen (as N)
Total
Phosphorous
20
80
5
20
18

19. Treatment
Processes
Physical, chemical, or biological processes.
What are the things removed in a municipal
wastewater treatment?
BOD, SS, pathogen, and nutrients (?)
30/30 Rule (BOD5 and TSS)
301H waiver for secondary treatment
discharge to the ocean
Pretreatment of industrial wastes
19

20. Pretreatment of Industrial Wastewaters
Industrial wastewaters must be pretreated
prior to being discharged to municipal sewer
system.
Approach is to remove materials that will not
be treated by municipal system.
Local authority must monitor and regulate
industrial discharges.
Pretreatment requirements set by U.S. EPA.
20

21. Overview of Municipal
Wastewater Treatment
Preliminary treatment – removes
materials that can cause operational
problems, equalization optional.
Primary treatment – remove ~60% of
solids and ~35% of BOD5.
Secondary treatment – remove ~85%
of BOD5 and solids (and nutrients
now).
Advanced treatment – varies: 95%+
of BOD5 and solids, N, P (polishing).
21

22. Preliminary Treatment –
Bar racks
Purpose
 remove larger
objects
Solid material stored in
hopper and sent to
landfill
Mechanically or
manually cleaned
22

23. Bar rack (on right) in service.
Comminuter (on left) out of service
23

24. Preliminary
Treatment –
Grit chambers
Purpose: remove inert dense material, such as
sand, broken glass, silt and pebbles
Avoid abrasion of pumps and other mechanical
devices
Material is called “grit”
24

25. (Aerated) Grit Chamber
Remove sand, coffee ground,
egg shell…
Typical retention time = 2 – 5
minutes, based on Q peak.
L:W = 3:1 (typ.)
Air flow rate = 3 cfm/ft length
or 0.3 m3/m/m (typ.)
Two tanks in parallel
Depth = 6 – 15 ft
25

26. (Aerated) Grit Chamber
Design AGC for Q = 10 MGD,
PF = 1.5, and two tanks in
parallel, D = 6’.
Q peak = 10*1.5/2 = 7.5 MGD
per tank
V = (7,500,000)(3/1440)/7.48
= 2090 ft3
A = 2090/(6) = 350 ft2 =
(3W)(W)
W = 11 ft, L = 33 ft
Air supply = (33)(3) = 100 cfm
for each tank
26

27. Primary
Treatment
Primary Sedimentation Tank (PST)
Physical process.
Remove ~55% SS; ~ 35% BOD
τ ~ 2 hours
SOR = 1,000 gpd/ft2
Weir loading = 20,000 gpd/ft
D ~ 10 ft
27

28. Primary
Treatment
(Example 6-4)
Q = 0.15 m3/s
L x W x D = 40m x 10m x 2m
Weir length = 75 m
τ = V/Q = 1.5 hr
Overflow rate = Q/A = 32 m/d
Weir loading rate = Q/L = 173 m3/d/m
28

29. Fig 6-12: Primary settling tank
29

30. Secondary
Treatment
Main Purpose:
Provide BOD removal
- M/O convert organic
wastes into stabilized
compounds (similar
to self-purification of
a stream or river).
Secondary Purpose:
Additional removal of
suspended solids - to
have a clarified
effluent.
Effectiveness depends on
availability of high
density of
microorganisms
good contact between
organisms and wastes
availability of wastes
favorable temperature
favorable pH
absence of toxic
compounds
30

31. Secondary Treatment
Biological Treatment
Activated Sludge
Trickling Filter
Rotating Contactor Beds
Secondary Clarification
Disinfection
31

32. Secondary Treatment
Biological process.
Remove >80% BOD
Organics removal
and clarified
effluent.
Suspended growth
Attached growth
Aerobic
Dispersed Growth
 Activated sludge
 Oxidation
ditches/ponds
 Aerated lagoons,
stabilization ponds
Fixed Growth
 Trickling filters
 Rotating Biological
Contactors (RBCs)
32

33. Biology of Wastewater
- Classification
Electron Acceptor
 Obligate aerobes
 Facultative anaerobes
 obligate anaerobes
 anoxic conditions
Carbon source
 Heterotrophs (organics)
 Autotrophs (CO2)
Energy source
 Phototrophs (light)
 Chemotrophs (organics)
33

34. Biology of Wastewater
- Classification
Important Organisms in
Wastewater Treatment
 Bacteria
 Fungi
 Algae
 Protozoa
 Rotifers
Temperature Ranges
 psychrophiles (0 - 20°C)
 mesophiles (20 - 40°C)
 thermophiles (45 - 60°C)
34

35. Heterogeneous microorganism population employed in
wastewater treatment
35

36. Fig 6-19: Conventional activated sludge plant
36

37. Activated Sludge
Q
So
MLVSS = 0.8
MLSS
MCRT, θ
X, V
Qe, Xe, S
RAS, QR, XR
WAS, Qw, XR
37

38. Activated
Sludge ….
Typical Values
 Mixed liqueur aerated 4-8 hours
 8 m3 of air per m3 of wastewater treated
 Sludge return can be 30 -100% of wastewater flow
 MLSS = 3,000 mg/L
 F/M = 0.4/d
Sludge return
 Ideally enough sludge should be returned to keep
the mass of microbes in reactor constant.
 θc = mean cell residence time (MCRT).
 Typical (3 - 15 days)
38

39. Primary settling tanks in foreground followed by
aeration tanks and circular secondary settling tanks
39

40. Activated sludge aeration tank
40

41. Activated Sludge - F/M parameter
Low F/M (low rate of wasting)
 starved organisms
 more complete degradation
 larger, more costly aeration tanks
 more O2 required
 higher power costs (to supply O2)
 less sludge to handle
High F/M (high rate of wasting)
 organisms are saturated with food
 low treatment efficiency
41

42. Q
So
Activated Sludge ….
MLVSS = 0.8
MLSS
MCRT, θ X, V
Qe, Xe, S
RAS, QR, XR
WAS, Qw, XR
F
QSo
So
=
=
M
θX
VX
QSo
Volumetric Loading Rate =
V
VX
VX
θ c (or MCRT ) =
≈
Q w X w + Qe X e Q w X w
Qr
X
=
Q + Qr X r
θ c Y ( So − S )
X=
θ 1 + k dθ c
and
Qr
R=
Q
K s (1 + θ c k d )
S=
θ c ( µ m − kd ) − 1
42

43. Activated Sludge (Examples 6-5 & 6-7)
Q = 0.15 m3/s; BOD5 = 84 mg/L
Ks = 100 mg/L; µm= 2.5/d; kd = 0.05/d; Y = 0.5 mg
VSS/mg BOD5 removed; MLVSS = 2000 mg/L
BOD5 of the effluent SS = 63% of SS
30/30 requirements
S = BOD5 allowed – BOD5 in SS
= 30 - (30)(63%) = 11.1
Q
K s (1 + θ c k d )
S=
θ c (µ m − kd ) − 1
θc = 5 days
So
MLVSS = 0.8
MLSS
MCRT, θ X, V
Qe, Xe, S
RAS, QR, XR
WAS, Qw, XR
43

44. Activated Sludge
(Examples 6-5 & 6-7)
Q
So
MLVSS = 0.8
MLSS
MCRT, θ X, V
θ c Y ( So − S )
X=
θ 1 + k dθ c
Qe, Xe, S
RAS, QR, XR
WAS, Qw, XR
θ = 0.073 d = 1.8 hr (short)
V = τQ = 970 m3
 F/M = 0.56 mg BOD5/mg MLVSS/d
F
QSo
So
=
=
M
θX
VX
44

45. Activated Sludge (Ex. 6-8)
Q = 0.15 m3/s; BOD5 = 84 mg/L
V = 970 m3, X = 2,000 mg/L, and θc = 5 days
(20% of MLVSS in aeration tanks is wasted every
day)
Assume XR (same as Xw) = 3,986 mg/L
θ c (or MCRT ) =
VX
VX
≈
Q w X w + Qe X e Q w X w
 Qw = 97.3 m3/d
= 0.0011 m3/s ( ~0.5%Q)
Volumetric Loading Rate =
Q
S
o
QS o
=
V
[(0.15)(86400)](84)
= 1,122 mg / m 3 / d
970
MLVSS = 0.8
MLSS
MCRT, θ X, V
Qe, Xe, S
RAS, QR, XR
WAS, Qw,
XR
45