Module 4: Fundamentals of
Wastewater Treatment
Wastewater Treatment Plant
Operator Training
Unit 1–Preliminary Treatment
Learning Objectives
• Explain the general purpose of preliminary treatment.
• Explain the purpose of screening, grit removal, and
pre-aeration.
• Differentiate between manually and mechanically
cleaned racks and screens.
• Define differences between screening and
comminution.
• Describe safe disposal of screenings and grit.
2
Manually Cleaned Bar Screen
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
3
Mechanically Cleaned Bar Screen
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
4
Aerated Grit Chamber
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
5
Cyclone Separator
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
6
Grit Washer
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
7
Comminutor
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
8
Comminutor with By-Pass Screen
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
9
Barminutor
AERATION TANK
Diagram excerpted from Chapter 4: Racks, Screens, Comminutors and Grit
Removal. In Operation of Wastewater Treatment Plants Volume I.
10
Unit 2–Primary Treatment: Sedimentation & Flotation
Learning Objectives
• Explain sedimentation and flotation
principles.
• List factors that indicate a clarifier is not
performing properly.
• Use mathematical formulas to solve for
detention time, weir overflow, surface
loading, and solids loading.
11
Detention Time Formulas
Formulas
Detention Time, hr. = Tank Volume, cu ft x 7.5 gal/cu ft x 24 hr/day
Flow, gal/day
Rectangular Tank Volume, cu ft = Length, ft x Width, ft x Height (Depth), ft
Area of Circle, ft2 = (0.785)(Diameter2) or ()(Radius2)
Note:  = 3.14
Circular Tank Volume, cu ft = Area x Height (Depth), ft
Circular Tank Volume, cu ft = (0.785)(Diameter, ft)2 x Height (Depth), ft or
(3.14)(Radius, ft)2 x Height (Depth), ft
12
Detention Time: Sample 2.1
What is the detention time when…
•
The flow is 3.0 million gallons per day (MGD)
or 3,000,000 gal/day, and
•
Tank dimensions are 60 feet long by 30 feet
wide by 10 feet deep?
13
Step #1 - Volume
Given:
Volume = 60 feet by 30 feet by 10 feet
= 18,000 cu ft
14
Step #2 - Flow
Given:
Flow = 3.0 million gallons per day (MGD)
or 3,000,000 gal/day
15
Step #3 - Calculation
Detention
Time, hr
= Tank Volume, cu ft x 7.5 gal/cu ft x 24 hr/day
Flow, gal/day
= 18,000 cu ft X 7.5 gal/cu ft x 24 hr/day
3,000,000 gal/day
= 3,240,000 gal/hr/day
3.0 MGD
= 1.08 hours
16
Detention Time: Sample 2.2
What is the detention time when…
•
The flow is 2.5 million gallons per day (MGD),
and
•
Circular clarifier is 60 ft in diameter with a
depth of 12 ft?
17
Step #1 - Volume
Reminder:
•
Circular Tank Volume, cu ft = 0.785 x
(Diameter, ft)2 x Depth, ft
•
Volume = (0.785) x (60 ft)2 x 12 ft deep
= 33,912 cu ft
18
Step #2 - Flow
Given:
Flow = 2.5 million gallons per day (MGD)
or 2,500,000 gal/day
19
Step #3 - Calculation
Detention
Time, hr
= 33,912 cu ft x 7.48 gal/cu ft x 24 hr/day
2.5 MGD
= 6,087,882 gal/hr/day
2,500,000 gal/day
= 2.44 hours
20
Weir Overflow Rate
Formulas
•
Weir Overflow, gpd/ft = Flow Rate, GPD
Length of Weir, ft
•
Length of Circular Weir = 3.14 x Weir
Diameter, ft
21
Weir Overflow Rate: Problem 2.1
What is the weir overflow rate when…
•
The flow rate into the unit is 3.5 MGD, and
•
The circular clarifier has a 75 foot diameter
overflow weir
22
Weir Overflow Rate: Problem 2.1
Weir overflow rate,
gpd/ft
= 3,500,000 gallons/day
3.14 x 75 feet
= 3,500,000 gal/day
235.5 feet
= 14,862 gpd/ft
23
Surface Loading Rate: Problem 2.2
What is the surface loading rate when…
•
The flow into a rectangular clarifier is 5.0 MGD
•
The clarifier is 40 feet wide by 110 feet long by 12
feet deep
–
Reminder:
Surface loading rate , gpd/ft2 = Flow Rate, gpd
Surface area, ft2
24
Surface Loading Rate: Problem 2.2
Surface loading rate,
gpd/ft2
= 5,000,000 gallons/day
40 ft x 110 feet
= 5,000,000 gal/day
4400 ft2
= 1,136 gpd/ft2
25
Solids Loading Guidelines
Pa DEP - Domestic
Wastewater Facilities
Manual
Operation of Wastewater
Treatment Plants, Vol I
Primary Clarifiers
Not considered
Not generally considered
Conventional Activated Sludge
Secondary Clarifiers
40 #/day/sq ft average, 50
peak
12 to 30 lbs/day/sq ft
Extended Aeration
Secondary Clarifiers
30 #/day/sq ft average, 50
peak
N/A
Nitrification Secondary Clarifiers:
Separate Nitrification Stage
30 average, 50 peak
N/A
45 average, 50 peak
N/A
Dissolved-Air Flotation
40 #/day/sq ft (w/o polymer
addition),
20 #/day sq ft (w polymer
addition)
5 to 40 lbs/day/sq ft
Sludge Thickening
5 to 12 #/day/sq ft
5 to 20 lbs/day/sq ft
Carbonaceous Stage
26
Solids Loading
Formulas
•
Solids Loading, lbs/day/ft2 =
Solids Applied, lbs/day
Surface Area, ft2
–
Solids Applied, lbs/day =
Flow, MGD x Conc., mg/L x 8.34 lbs/gal
27
Solids Loading: Problem 2.3
Calculate the solids loading at which a clarifier is
operating given the following…
• The circular clarifier has a diameter of 125 feet
• Forward flow is 6.0 MGD and the return sludge flow
is 2.0 MGD
• MLSS is 4.000 mg/L
28
Step # 1 - Solids Applied
Reminder:
Solids Applied,
lbs/day
= Flow, MGD x MLSS conc., mg/L x 8.34 lbs/gal
Solids Applied = 8 MGD x 4,000 mg/L x 8.34 lbs/gal
= 266,880 lbs/day
29
Step # 2 – Surface Area
Given: The circular clarifier has a diameter of 125 feet
Area of Circle, ft2 = (0.785)(Diameter)2
= (0.785)(125 ft)2
= (0.785)(15,625 ft2)
= 12,266 ft2
30
Step # 3 – Solids Loading
Solids Loading,
lbs/day/ft2
= Solids Applied, lbs/day
Surface Area, ft2
= 266,880 lbs/day
12,266 ft2
= 22 lbs/day/ft2
31
Unit 3–Overview of Biological Secondary Treatment
Learning Objectives
• List four biological secondary treatment processes.
• Explain the principles of the trickling filter process.
• Identify the different types of trickling filters.
• Explain the principles of the rotating biological contactor
(RBC) process.
• Explain the principles of the activated sludge process.
• List the three waste treatment pond classifications and
explain the principles of each.
32
Trickling Filter Process
Trickling
Filter Process
Filter
Pump
Station
Raw
Wastewater
Preliminary
Treatment
Primary
Clarifier
Wet Pit
Filter
Underflow
Distributor
Secondary
Clarifier
Influent
Trickling
Filter
Secondary
Clarifier
Primary
AERATION TANKEffluent
Solids
Handling
Chlorine
Contact
Basin
Recirculation
Waste
Solids
TRICKLING FILTER PROCESS FLOW SCHEMATIC
33
Plant
Effluent
Trickling Filter
AERATION TANK
Diagram excerpted from Chapter 6: Trickling Filters. In Operation of
Wastewater Treatment Plants Volume I.
34
Rotating Biological Contactor Process
RBC Process
Primary
Effluent
Shafts
No. 1
No. 2
No. 3
No. 4
Secondary
Clarifier
Influent
Media (Typ)
Raw
Wastewater
Preliminary
Treatment
Primary
Clarifier
RBC Reactors
Secondary
Clarifier
Chlorine
Contact
Basin
Tank (Typ)
Baffle (Typ)
AERATION TANK
Solids
Handling
Waste
Solids
ROTATING BIOLOGICAL CONTRACTOR PROCESS FLOW SCHEMATIC
35
Plant
Effluent
Complete Mix Activated Sludge
Primary
Effluent
Raw
Wastewater
Preliminary
Treatment
Primary
Clarifier
Aeration Tank
or Reactor
Secondary
Clarifier
Return Activated Sludge
Waste
Solids
Solids
Handling
Waste Activated Sludge
CONVENTIONAL ACTIVATED SLUDGE SCHEMATIC
(COMPLETE MIX)
36
Chlorine
Contact
Basin
Plant
Effluent
Contact Stabilization Schematic
Raw
Wastewater
Waste
Solids
Preliminary
Treatment
Solids
Handling
Aeration Contact Tank
or Reactor
Waste
AERATION TANK
Activated
Sludge
Reaeration Tank
or Reactor
Secondary
Clarifier
Chlorine
Contact
Basin
Return
Activated
Sludge
CONTACT STABILIZATION ACTIVATED SLUDGE SCHEMATIC
37
Plant
Effluent
Extended Aeration Schematic
Raw
Wastewater
Preliminary
Treatment
Aeration Tank
or Reactor
Clarifier
Chlorine
Contact
Basin
Return Activated Sludge
AERATION TANK
Waste
Solids
Solids
Handling
Waste Activated Sludge
EXTENDED AERATION ACTIVATED SLUDGE SCHEMATIC
38
Plant
Effluent
Two Unit SBR Time Chart
Time Period (hrs)
Unit #1
Unit #2
0-1
Fill
Aeration
1-2
Fill
Settle
2-3
Fill / Aeration
Settle
3-4
Fill / Aeration
Draw
4-5
Aeration
Fill
5-6
Settle
Fill
6-7
Settle
Fill / Aeration
7-8
Draw
Fill / Aeration
39
Oxidation Ditch Schematic
Rotor (Typ)
Level
Control
Weir
Raw
Wastewater
Preliminary
Treatment
Chlorine
Contact
Basin
Final
Clarifier
Oxidation Ditch
AERATION TANK
Return
Sludge
Pumping
Return Sludge
Solids
Handling
Waste
Solids
Waste
Sludge
OXIDATION DITCH SCHEMATIC40
Plant
Effluent