Page 1 of 110
Illinois Wastewater Operator Class 1 Exam
Actual exam Questions with Correct Answers
and explanations LATEST THIS YEAR -just
released
Summarized Exam Coverage Outline
The Illinois Class 1 exam is the highest level of municipal wastewater certification, requiring significant
experience and advanced knowledge . The exam content is governed by 35 Illinois Administrative Code
380.420 .
1. Treatment Processes (Advanced)
• Activated Sludge: Process control for conventional, extended aeration, SBR, oxidation ditch;
managing F/M ratio, SVI, sludge age, and addressing bulking/foaming .
• Fixed Film Systems: Trickling filters (standard/high-rate), RBCs (rotating biological contactors);
organic/hydraulic loading, temperature effects, ponding.
• Advanced/Nutrient Removal: Biological nutrient removal (BNR) for nitrogen
(nitrification/denitrification) and phosphorus (bio-P/chemical precipitation) .
• Sludge Processing: Anaerobic digestion (methane production, volatile solids reduction), aerobic
digestion, thickening, dewatering (centrifuge, belt press) .
• Tertiary Treatment: Filtration (sand/dual media), disinfection (chlorine, UV, ozone), effluent
polishing .
2. Laboratory & Process Control
• Key Tests: BOD, COD, TSS, VSS, DO, pH, Alkalinity, Ammonia, Nitrate, Ortho-P, MLSS/MLVSS, SVI,
Microscopic examination (identifying filaments) .
• Calculations: Detention time, surface overflow rate (SOR), weir loading, SVI, F/M ratio, MCRT,
percent removal, pounds (lbs) formula, chlorination dosage, sludge age, gas production .
3. NPDES Permit Compliance
• Permit Limits: Understanding effluent limits (CBOD, TSS, Ammonia, pH, DO, Phosphorus),
monitoring frequency, reporting requirements .
• Sampling: Composite vs. grab sampling, 24-hour composites, flow-proportional sampling,
sample preservation, chain of custody.
4. Safety & Administration
• Safety: Confined space entry (permit-required), lock-out/tag-out (LOTO), H2S gas monitoring,
chlorine handling (safety equipment), PPE, fall protection .
• Management: Recordkeeping (O&M manual, permit compliance reports), process control
strategies, troubleshooting, emergency response plans, staff supervision.
5. Collection Systems (Inflow & Infiltration - I&I)
• Sewers: Lift stations, pumps, force mains, gravity sewers, cleaning methods, identifying I&I
sources, manhole inspection, flow monitoring .
6. Illinois Specific Requirements
• Certification: Class 1 requires 6 years of experience (min 3 years hands-on), high school
diploma, and a passing exam score of 70 or higher .
• Credit System: Up to 3 years credit available for education/related experience .
200 Scenario-Based MCQs (Exam-Relevant)
Domain 1: Treatment Processes (Activated Sludge)
, Page 2 of 110
1. Which of the following is the primary purpose of the activated sludge process?
A. To screen out large debris
B. To remove settleable solids by gravity
C. To biologically oxidize dissolved and colloidal organic matter
D. To disinfect the wastewater before discharge
Answer: C
Rationale: Activated sludge uses a high concentration of microorganisms to consume biodegradable
organic matter, converting it to biological solids that can be settled out.
2. An operator notices the activated sludge has a thick, dark brown, greasy foam on the surface of the
aeration basin. What is the most likely cause?
A. Young sludge (low sludge age)
B. Nocardia or Microthrix parvicella filamentous bacteria
C. Low dissolved oxygen in the aeration basin
D. Excessive waste activated sludge removal
Answer: B
, Page 3 of 110
Rationale: Thick, greasy, dark brown foam is often caused by filamentous organisms like Nocardia,
which trap air bubbles and resist collapse.
3. What is the correct formula for calculating the Food to Microorganism (F/M) ratio?
A. (MLVSS) / (Influent BOD)
B. (Influent BOD) / (MLVSS)
C. (MLSS) x (WAS flow) / (Aeration volume)
D. (Influent TSS) / (MLVSS)
Answer: B
Rationale: F/M = (lbs of BOD entering aeration) / (lbs of MLVSS in aeration). It indicates the food
available per pound of microorganisms.
4. A Class 1 plant has an SVI (Sludge Volume Index) of 180 mL/g. What condition does this indicate?
A. Excellent settling sludge
B. Young sludge with good settling
C. Old sludge with good settling
D. Bulking sludge with poor settling characteristics
Answer: D
, Page 4 of 110
Rationale: An SVI over 150 mL/g typically indicates bulking sludge, often due to filamentous organisms,
leading to poor settling and high effluent TSS.
5. A facility experiences rising sludge in the secondary clarifier, where sludge blankets rise to the surface
days after settling. This is often caused by:
A. Denitrification occurring in the clarifier
B. Excessive wasting of sludge
C. Low mixed liquor suspended solids (MLSS)
D. High dissolved oxygen in the return sludge
Answer: A
Rationale: Rising sludge is caused by denitrification (conversion of nitrate to nitrogen gas) in the
clarifier; the gas bubbles attach to sludge, making it float.
6. You observe pin floc in the final effluent. This most likely indicates:
A. Old sludge (high sludge age)
B. Young sludge (low sludge age) with high shearing forces
C. Excessive filamentous bacteria
D. Low incoming BOD load
Illinois Wastewater Operator Class 1 Exam
Actual exam Questions with Correct Answers
and explanations LATEST THIS YEAR -just
released
Summarized Exam Coverage Outline
The Illinois Class 1 exam is the highest level of municipal wastewater certification, requiring significant
experience and advanced knowledge . The exam content is governed by 35 Illinois Administrative Code
380.420 .
1. Treatment Processes (Advanced)
• Activated Sludge: Process control for conventional, extended aeration, SBR, oxidation ditch;
managing F/M ratio, SVI, sludge age, and addressing bulking/foaming .
• Fixed Film Systems: Trickling filters (standard/high-rate), RBCs (rotating biological contactors);
organic/hydraulic loading, temperature effects, ponding.
• Advanced/Nutrient Removal: Biological nutrient removal (BNR) for nitrogen
(nitrification/denitrification) and phosphorus (bio-P/chemical precipitation) .
• Sludge Processing: Anaerobic digestion (methane production, volatile solids reduction), aerobic
digestion, thickening, dewatering (centrifuge, belt press) .
• Tertiary Treatment: Filtration (sand/dual media), disinfection (chlorine, UV, ozone), effluent
polishing .
2. Laboratory & Process Control
• Key Tests: BOD, COD, TSS, VSS, DO, pH, Alkalinity, Ammonia, Nitrate, Ortho-P, MLSS/MLVSS, SVI,
Microscopic examination (identifying filaments) .
• Calculations: Detention time, surface overflow rate (SOR), weir loading, SVI, F/M ratio, MCRT,
percent removal, pounds (lbs) formula, chlorination dosage, sludge age, gas production .
3. NPDES Permit Compliance
• Permit Limits: Understanding effluent limits (CBOD, TSS, Ammonia, pH, DO, Phosphorus),
monitoring frequency, reporting requirements .
• Sampling: Composite vs. grab sampling, 24-hour composites, flow-proportional sampling,
sample preservation, chain of custody.
4. Safety & Administration
• Safety: Confined space entry (permit-required), lock-out/tag-out (LOTO), H2S gas monitoring,
chlorine handling (safety equipment), PPE, fall protection .
• Management: Recordkeeping (O&M manual, permit compliance reports), process control
strategies, troubleshooting, emergency response plans, staff supervision.
5. Collection Systems (Inflow & Infiltration - I&I)
• Sewers: Lift stations, pumps, force mains, gravity sewers, cleaning methods, identifying I&I
sources, manhole inspection, flow monitoring .
6. Illinois Specific Requirements
• Certification: Class 1 requires 6 years of experience (min 3 years hands-on), high school
diploma, and a passing exam score of 70 or higher .
• Credit System: Up to 3 years credit available for education/related experience .
200 Scenario-Based MCQs (Exam-Relevant)
Domain 1: Treatment Processes (Activated Sludge)
, Page 2 of 110
1. Which of the following is the primary purpose of the activated sludge process?
A. To screen out large debris
B. To remove settleable solids by gravity
C. To biologically oxidize dissolved and colloidal organic matter
D. To disinfect the wastewater before discharge
Answer: C
Rationale: Activated sludge uses a high concentration of microorganisms to consume biodegradable
organic matter, converting it to biological solids that can be settled out.
2. An operator notices the activated sludge has a thick, dark brown, greasy foam on the surface of the
aeration basin. What is the most likely cause?
A. Young sludge (low sludge age)
B. Nocardia or Microthrix parvicella filamentous bacteria
C. Low dissolved oxygen in the aeration basin
D. Excessive waste activated sludge removal
Answer: B
, Page 3 of 110
Rationale: Thick, greasy, dark brown foam is often caused by filamentous organisms like Nocardia,
which trap air bubbles and resist collapse.
3. What is the correct formula for calculating the Food to Microorganism (F/M) ratio?
A. (MLVSS) / (Influent BOD)
B. (Influent BOD) / (MLVSS)
C. (MLSS) x (WAS flow) / (Aeration volume)
D. (Influent TSS) / (MLVSS)
Answer: B
Rationale: F/M = (lbs of BOD entering aeration) / (lbs of MLVSS in aeration). It indicates the food
available per pound of microorganisms.
4. A Class 1 plant has an SVI (Sludge Volume Index) of 180 mL/g. What condition does this indicate?
A. Excellent settling sludge
B. Young sludge with good settling
C. Old sludge with good settling
D. Bulking sludge with poor settling characteristics
Answer: D
, Page 4 of 110
Rationale: An SVI over 150 mL/g typically indicates bulking sludge, often due to filamentous organisms,
leading to poor settling and high effluent TSS.
5. A facility experiences rising sludge in the secondary clarifier, where sludge blankets rise to the surface
days after settling. This is often caused by:
A. Denitrification occurring in the clarifier
B. Excessive wasting of sludge
C. Low mixed liquor suspended solids (MLSS)
D. High dissolved oxygen in the return sludge
Answer: A
Rationale: Rising sludge is caused by denitrification (conversion of nitrate to nitrogen gas) in the
clarifier; the gas bubbles attach to sludge, making it float.
6. You observe pin floc in the final effluent. This most likely indicates:
A. Old sludge (high sludge age)
B. Young sludge (low sludge age) with high shearing forces
C. Excessive filamentous bacteria
D. Low incoming BOD load
