Wastewater Treatment Operator
Certification Examination
Tests 2 & 3 — Grade/Class 2 & 3
────────────────────────────────────────
Academic Assessment Review
Fiscal Year 2026–2027 | 160 Questions
Association of Boards of Certification (ABC) / State Environmental Agency
Aligned with ABC Need-to-Know Criteria & KSAs
, Wastewater Operator Certification Exam — Tests 2 & 3
Table of Contents
Introduction .............................................................................................................................................. 3
Abstract ....................................................................................................................................................... 3
Wastewater Characteristics & Sampling Procedures ................................................................... 3
Preliminary & Primary Treatment Processes ................................................................................. 8
Secondary Biological Treatment ........................................................................................................ 13
Solids Handling & Biosolids Management ..................................................................................... 20
Disinfection & Effluent Requirements ............................................................................................ 26
Process Control Calculations ............................................................................................................. 33
Safety & Regulatory Compliance ....................................................................................................... 38
Maintenance & Troubleshooting ...................................................................................................... 43
Laboratory Procedures & Data Interpretation ............................................................................. 49
Scenario-Based Operational Decision-Making ............................................................................ 52
References................................................................................................................................................. 57
Page 2 of 57
, Wastewater Operator Certification Exam — Tests 2 & 3
Introduction
This Wastewater Treatment Operator Certification Examination for Tests 2 and 3 (Grade/Class 2 and
Grade/Class 3) represents a comprehensive practice assessment aligned with the Association of
Boards of Certification (ABC) Need-to-Know Criteria and the knowledge, skills, and abilities (KSAs)
required for intermediate to advanced level wastewater treatment operators. The exam encompasses
160 multiple-choice questions spanning ten critical operational domains, including wastewater
characteristics and sampling, preliminary and primary treatment, secondary biological treatment,
solids handling and biosolids management, disinfection and effluent requirements, process control
calculations, safety and regulatory compliance, maintenance and troubleshooting, laboratory
procedures, and scenario-based operational decision-making. Each question is accompanied by the
correct answer (displayed in bold green) and a detailed rationale explaining the technical basis for the
response. This assessment is designed to support operator preparation for state environmental agency
certification examinations and to reinforce competency in evidence-based process control, regulatory
compliance under the National Pollutant Discharge Elimination System (NPDES), and professional
judgment in municipal wastewater facility operations.
Abstract
This document presents a 160-question practice examination for the Wastewater Treatment Operator
Certification at the Grade/Class 2 and Grade/Class 3 levels, structured in alignment with the
Association of Boards of Certification (ABC) examination framework. The assessment covers ten core
domains including treatment process knowledge, regulatory compliance, process control calculations,
safety protocols, and scenario-based operational decision-making. Questions are designed to evaluate
proficiency in biological and physical treatment unit operations, solids management, disinfection
practices, laboratory analysis, and mathematical problem-solving essential for professional
wastewater treatment facility management. The exam format mirrors the structure and content
emphasis of actual state-administered certification examinations, providing operators with a
comprehensive preparation tool for achieving certification and advancing professional competence in
the wastewater treatment field.
Keywords: Wastewater Treatment Operator Certification, ABC Exam, Grade 2, Grade 3, NPDES
Compliance, Activated Sludge, Process Control, Biosolids Management, Disinfection, OSHA Safety,
Process Control Calculations
Wastewater Characteristics & Sampling Procedures
1. What does the BOD₅ test measure?
A) The amount of oxygen required by bacteria to stabilize organic matter under
aerobic conditions over a 5-day period at 20 °C
B) The total amount of dissolved oxygen consumed by chemical oxidation of organic and
inorganic matter
C) The rate of oxygen transfer from air into the wastewater sample at standard temperature and
pressure
D) The concentration of carbonaceous organic material expressed as milligrams of carbon per liter
The 5-day Biochemical Oxygen Demand (BOD₅) measures the dissolved oxygen consumed by
microorganisms decomposing organic matter under controlled aerobic conditions (20 °C, dark
Page 3 of 57
, Wastewater Operator Certification Exam — Tests 2 & 3
incubation, 5 days). It is the most widely used indicator of organic strength in wastewater and a
key parameter in NPDES discharge permits.
2. What is the primary difference between BOD and CBOD?
A) CBOD is measured at 25 °C, while BOD is measured at 20 °C
B) BOD is a chemical test, while CBOD is a biological test
C) CBOD always yields a higher result than the standard BOD test because it includes nitrogenous
demand
D) CBOD measures only carbonaceous oxygen demand, while BOD includes both
carbonaceous and nitrogenous demand
Carbonaceous BOD (CBOD) measures only the oxygen demand from carbon-based organic
matter decomposition. Standard BOD includes both carbonaceous and nitrogenous oxygen
demand (from nitrification), which can cause elevated results in samples with high ammonia.
CBOD uses a nitrification inhibitor (e.g., TCMP) to exclude nitrogenous demand.
3. Which statement best describes the relationship between Chemical Oxygen Demand
(COD) and BOD?
A) COD results are typically lower than BOD results for the same wastewater sample
B) COD measures both biodegradable and non-biodegradable organic matter, so
COD values are generally higher than BOD values
C) COD and BOD always produce equivalent results when the sample contains only domestic
wastewater
D) COD is a biological test that requires a 5-day incubation period
COD uses a strong chemical oxidant (dichromate) and acid digestion to oxidize both
biodegradable and non-biodegradable organics, so the measured value is almost always greater
than BOD. For domestic wastewater, the COD-to-BOD ratio typically ranges from 1.5:1 to 3:1.
COD provides results in 2–3 hours, making it useful for rapid process control.
4. A technician filters 250 mL of wastewater through a 0.45-micron filter, dries the
residue at 104 °C, and weighs it. The filter weight increased by 85 mg. What is the TSS
concentration in mg/L?
A) 85 mg/L
B) 170 mg/L
C) 340 mg/L
D) 425 mg/L
TSS (mg/L) = (Weight of dried residue in mg) / (Sample volume in L). The sample volume is 250
mL = 0.250 L. TSS = 85 mg / 0.250 L = 340 mg/L. TSS measures the non-dissolved, filterable
fraction of solids and is critical for evaluating clarifier and filter performance.
5. Total Dissolved Solids (TDS) are measured by which procedure?
A) Filtering the sample through a 0.45-micron filter and weighing the material retained on the
filter
B) Evaporating the filtrate that passes through a 0.45-micron filter and drying the
residue at 180 °C
C) Centrifuging the sample at 3,000 rpm and weighing the settled material
D) Igniting a dried sample at 550 °C and measuring the weight loss
Page 4 of 57
Certification Examination
Tests 2 & 3 — Grade/Class 2 & 3
────────────────────────────────────────
Academic Assessment Review
Fiscal Year 2026–2027 | 160 Questions
Association of Boards of Certification (ABC) / State Environmental Agency
Aligned with ABC Need-to-Know Criteria & KSAs
, Wastewater Operator Certification Exam — Tests 2 & 3
Table of Contents
Introduction .............................................................................................................................................. 3
Abstract ....................................................................................................................................................... 3
Wastewater Characteristics & Sampling Procedures ................................................................... 3
Preliminary & Primary Treatment Processes ................................................................................. 8
Secondary Biological Treatment ........................................................................................................ 13
Solids Handling & Biosolids Management ..................................................................................... 20
Disinfection & Effluent Requirements ............................................................................................ 26
Process Control Calculations ............................................................................................................. 33
Safety & Regulatory Compliance ....................................................................................................... 38
Maintenance & Troubleshooting ...................................................................................................... 43
Laboratory Procedures & Data Interpretation ............................................................................. 49
Scenario-Based Operational Decision-Making ............................................................................ 52
References................................................................................................................................................. 57
Page 2 of 57
, Wastewater Operator Certification Exam — Tests 2 & 3
Introduction
This Wastewater Treatment Operator Certification Examination for Tests 2 and 3 (Grade/Class 2 and
Grade/Class 3) represents a comprehensive practice assessment aligned with the Association of
Boards of Certification (ABC) Need-to-Know Criteria and the knowledge, skills, and abilities (KSAs)
required for intermediate to advanced level wastewater treatment operators. The exam encompasses
160 multiple-choice questions spanning ten critical operational domains, including wastewater
characteristics and sampling, preliminary and primary treatment, secondary biological treatment,
solids handling and biosolids management, disinfection and effluent requirements, process control
calculations, safety and regulatory compliance, maintenance and troubleshooting, laboratory
procedures, and scenario-based operational decision-making. Each question is accompanied by the
correct answer (displayed in bold green) and a detailed rationale explaining the technical basis for the
response. This assessment is designed to support operator preparation for state environmental agency
certification examinations and to reinforce competency in evidence-based process control, regulatory
compliance under the National Pollutant Discharge Elimination System (NPDES), and professional
judgment in municipal wastewater facility operations.
Abstract
This document presents a 160-question practice examination for the Wastewater Treatment Operator
Certification at the Grade/Class 2 and Grade/Class 3 levels, structured in alignment with the
Association of Boards of Certification (ABC) examination framework. The assessment covers ten core
domains including treatment process knowledge, regulatory compliance, process control calculations,
safety protocols, and scenario-based operational decision-making. Questions are designed to evaluate
proficiency in biological and physical treatment unit operations, solids management, disinfection
practices, laboratory analysis, and mathematical problem-solving essential for professional
wastewater treatment facility management. The exam format mirrors the structure and content
emphasis of actual state-administered certification examinations, providing operators with a
comprehensive preparation tool for achieving certification and advancing professional competence in
the wastewater treatment field.
Keywords: Wastewater Treatment Operator Certification, ABC Exam, Grade 2, Grade 3, NPDES
Compliance, Activated Sludge, Process Control, Biosolids Management, Disinfection, OSHA Safety,
Process Control Calculations
Wastewater Characteristics & Sampling Procedures
1. What does the BOD₅ test measure?
A) The amount of oxygen required by bacteria to stabilize organic matter under
aerobic conditions over a 5-day period at 20 °C
B) The total amount of dissolved oxygen consumed by chemical oxidation of organic and
inorganic matter
C) The rate of oxygen transfer from air into the wastewater sample at standard temperature and
pressure
D) The concentration of carbonaceous organic material expressed as milligrams of carbon per liter
The 5-day Biochemical Oxygen Demand (BOD₅) measures the dissolved oxygen consumed by
microorganisms decomposing organic matter under controlled aerobic conditions (20 °C, dark
Page 3 of 57
, Wastewater Operator Certification Exam — Tests 2 & 3
incubation, 5 days). It is the most widely used indicator of organic strength in wastewater and a
key parameter in NPDES discharge permits.
2. What is the primary difference between BOD and CBOD?
A) CBOD is measured at 25 °C, while BOD is measured at 20 °C
B) BOD is a chemical test, while CBOD is a biological test
C) CBOD always yields a higher result than the standard BOD test because it includes nitrogenous
demand
D) CBOD measures only carbonaceous oxygen demand, while BOD includes both
carbonaceous and nitrogenous demand
Carbonaceous BOD (CBOD) measures only the oxygen demand from carbon-based organic
matter decomposition. Standard BOD includes both carbonaceous and nitrogenous oxygen
demand (from nitrification), which can cause elevated results in samples with high ammonia.
CBOD uses a nitrification inhibitor (e.g., TCMP) to exclude nitrogenous demand.
3. Which statement best describes the relationship between Chemical Oxygen Demand
(COD) and BOD?
A) COD results are typically lower than BOD results for the same wastewater sample
B) COD measures both biodegradable and non-biodegradable organic matter, so
COD values are generally higher than BOD values
C) COD and BOD always produce equivalent results when the sample contains only domestic
wastewater
D) COD is a biological test that requires a 5-day incubation period
COD uses a strong chemical oxidant (dichromate) and acid digestion to oxidize both
biodegradable and non-biodegradable organics, so the measured value is almost always greater
than BOD. For domestic wastewater, the COD-to-BOD ratio typically ranges from 1.5:1 to 3:1.
COD provides results in 2–3 hours, making it useful for rapid process control.
4. A technician filters 250 mL of wastewater through a 0.45-micron filter, dries the
residue at 104 °C, and weighs it. The filter weight increased by 85 mg. What is the TSS
concentration in mg/L?
A) 85 mg/L
B) 170 mg/L
C) 340 mg/L
D) 425 mg/L
TSS (mg/L) = (Weight of dried residue in mg) / (Sample volume in L). The sample volume is 250
mL = 0.250 L. TSS = 85 mg / 0.250 L = 340 mg/L. TSS measures the non-dissolved, filterable
fraction of solids and is critical for evaluating clarifier and filter performance.
5. Total Dissolved Solids (TDS) are measured by which procedure?
A) Filtering the sample through a 0.45-micron filter and weighing the material retained on the
filter
B) Evaporating the filtrate that passes through a 0.45-micron filter and drying the
residue at 180 °C
C) Centrifuging the sample at 3,000 rpm and weighing the settled material
D) Igniting a dried sample at 550 °C and measuring the weight loss
Page 4 of 57
