South Carolina Physical/Chemical Wastewater Operator Class C Exam
Practice Questions and Correct Answers
1: What is the primary purpose of primary treatment in a wastewater treatment
plant?
A. To remove dissolved organic matter through biological processes
B. To remove settleable and floatable solids through physical processes
C. To disinfect effluent before discharge
D. To remove nutrients like nitrogen and phosphorus
CORRECT ANSWER: B. To remove settleable and floatable solids through physical
processes
Rationale: Primary treatment uses physical processes—primarily sedimentation in
primary clarifiers—to remove settleable solids (sludge) and floatable materials
(scum, grease). It typically removes 50-70% of suspended solids and 25-40% of
BOD. Biological processes occur in secondary treatment; disinfection is tertiary;
nutrient removal is advanced treatment.
2: Which chemical is commonly used for phosphorus removal in physical/chemical
wastewater treatment?
A. Sodium hypochlorite
B. Aluminum sulfate (alum) or ferric chloride
C. Hydrochloric acid
D. Sodium hydroxide
CORRECT ANSWER: B. Aluminum sulfate (alum) or ferric chloride
Rationale: Alum (Al₂(SO₄)₃) and ferric chloride (FeCl₃) are coagulants that react with
orthophosphate to form insoluble precipitates (aluminum phosphate, iron
phosphate) that can be removed by sedimentation or filtration. Sodium hypochlorite
is for disinfection; acids/bases adjust pH.
3: What does BOD stand for in wastewater treatment?
A. Biological Oxygen Demand
,B. Biochemical Oxygen Demand
C. Bacterial Organic Decomposition
D. Biological Oxidation Demand
CORRECT ANSWER: B. Biochemical Oxygen Demand
Rationale: BOD measures the amount of dissolved oxygen consumed by
microorganisms while decomposing organic matter in wastewater over 5 days at
20°C (BOD₅). It is a key parameter for assessing organic pollution load and
treatment efficiency.
4: Which safety equipment is required when handling chlorine gas?
A. Safety goggles and gloves only
B. Self-contained breathing apparatus (SCBA) and chlorine leak repair kit
C. Hard hat and steel-toed boots only
D. Hearing protection and face shield
CORRECT ANSWER: B. Self-contained breathing apparatus (SCBA) and chlorine leak
repair kit
Rationale: Chlorine gas is toxic and heavier than air. OSHA and SC DHEC require
SCBA for emergency response, chlorine leak repair kits (A/B kits), and proper
ventilation. PPE must match the hazard; goggles/gloves alone are insufficient for gas
exposure.
5: Calculate the detention time (in hours) for a primary clarifier with a volume of
500,000 gallons and a flow rate of 2.5 MGD.
A. 2.4 hours
B. 4.8 hours
C. 1.2 hours
D. 6.0 hours
CORRECT ANSWER: B. 4.8 hours
Rationale: Detention time = Volume / Flow. Convert flow: 2.5 MGD = 2,500,000
gal/day. Detention time = 500,000 gal / 2,500,000 gal/day = 0.2 days. Convert to
,hours: 0.2 days × 24 hr/day = 4.8 hours. Proper detention time ensures adequate
solids settling.
6: What is the primary function of a bar screen in wastewater treatment?
A. To remove dissolved metals
B. To remove large debris like rags, sticks, and plastics
C. To disinfect incoming wastewater
D. To adjust pH of influent
CORRECT ANSWER: B. To remove large debris like rags, sticks, and plastics
Rationale: Bar screens (coarse screens) are the first unit process, removing large
solids that could damage pumps, clog pipes, or interfere with downstream
processes. Fine screens remove smaller particles; dissolved metals require
chemical treatment; disinfection occurs later.
7: Which parameter is used to measure the concentration of suspended solids in
wastewater?
A. BOD
B. TSS (Total Suspended Solids)
C. COD
D. pH
CORRECT ANSWER: B. TSS (Total Suspended Solids)
Rationale: TSS measures the dry weight of particles retained on a filter (typically
0.45-2.0 µm pore size), expressed in mg/L. It quantifies settleable and non-settleable
suspended matter. BOD measures oxygen demand from organic matter; COD
measures chemical oxygen demand; pH measures acidity/alkalinity.
8: What is the recommended pH range for optimal coagulation with alum in
phosphorus removal?
A. 4.0–5.5
B. 5.5–7.0
, C. 7.0–8.5
D. 8.5–10.0
CORRECT ANSWER: B. 5.5–7.0
Rationale: Alum coagulation is most effective in the pH range 5.5–7.0, where
aluminum hydroxide floc forms optimally to adsorb and precipitate phosphate.
Outside this range, floc formation is poor, reducing phosphorus removal efficiency.
pH adjustment may be needed before/after coagulation.
9: Which South Carolina agency regulates wastewater treatment plant permits and
effluent limits?
A. South Carolina Department of Labor
B. South Carolina Department of Health and Environmental Control (SC DHEC)
C. South Carolina Water Resources Commission
D. U.S. Environmental Protection Agency (EPA) Region 4 only
CORRECT ANSWER: B. South Carolina Department of Health and Environmental
Control (SC DHEC)
Rationale: SC DHEC administers the National Pollutant Discharge Elimination System
(NPDES) permit program in South Carolina under delegation from EPA. It issues
permits, sets effluent limits, conducts inspections, and enforces compliance for
wastewater facilities.
10: What is the purpose of a grit chamber in wastewater treatment?
A. To remove organic matter through biological processes
B. To remove sand, gravel, and other heavy inorganic solids
C. To disinfect wastewater before secondary treatment
D. To add chemicals for phosphorus removal
CORRECT ANSWER: B. To remove sand, gravel, and other heavy inorganic solids
Rationale: Grit chambers use controlled flow velocity (about 1 ft/s) to allow heavy
inorganic solids (grit) to settle while keeping lighter organic solids suspended.
Practice Questions and Correct Answers
1: What is the primary purpose of primary treatment in a wastewater treatment
plant?
A. To remove dissolved organic matter through biological processes
B. To remove settleable and floatable solids through physical processes
C. To disinfect effluent before discharge
D. To remove nutrients like nitrogen and phosphorus
CORRECT ANSWER: B. To remove settleable and floatable solids through physical
processes
Rationale: Primary treatment uses physical processes—primarily sedimentation in
primary clarifiers—to remove settleable solids (sludge) and floatable materials
(scum, grease). It typically removes 50-70% of suspended solids and 25-40% of
BOD. Biological processes occur in secondary treatment; disinfection is tertiary;
nutrient removal is advanced treatment.
2: Which chemical is commonly used for phosphorus removal in physical/chemical
wastewater treatment?
A. Sodium hypochlorite
B. Aluminum sulfate (alum) or ferric chloride
C. Hydrochloric acid
D. Sodium hydroxide
CORRECT ANSWER: B. Aluminum sulfate (alum) or ferric chloride
Rationale: Alum (Al₂(SO₄)₃) and ferric chloride (FeCl₃) are coagulants that react with
orthophosphate to form insoluble precipitates (aluminum phosphate, iron
phosphate) that can be removed by sedimentation or filtration. Sodium hypochlorite
is for disinfection; acids/bases adjust pH.
3: What does BOD stand for in wastewater treatment?
A. Biological Oxygen Demand
,B. Biochemical Oxygen Demand
C. Bacterial Organic Decomposition
D. Biological Oxidation Demand
CORRECT ANSWER: B. Biochemical Oxygen Demand
Rationale: BOD measures the amount of dissolved oxygen consumed by
microorganisms while decomposing organic matter in wastewater over 5 days at
20°C (BOD₅). It is a key parameter for assessing organic pollution load and
treatment efficiency.
4: Which safety equipment is required when handling chlorine gas?
A. Safety goggles and gloves only
B. Self-contained breathing apparatus (SCBA) and chlorine leak repair kit
C. Hard hat and steel-toed boots only
D. Hearing protection and face shield
CORRECT ANSWER: B. Self-contained breathing apparatus (SCBA) and chlorine leak
repair kit
Rationale: Chlorine gas is toxic and heavier than air. OSHA and SC DHEC require
SCBA for emergency response, chlorine leak repair kits (A/B kits), and proper
ventilation. PPE must match the hazard; goggles/gloves alone are insufficient for gas
exposure.
5: Calculate the detention time (in hours) for a primary clarifier with a volume of
500,000 gallons and a flow rate of 2.5 MGD.
A. 2.4 hours
B. 4.8 hours
C. 1.2 hours
D. 6.0 hours
CORRECT ANSWER: B. 4.8 hours
Rationale: Detention time = Volume / Flow. Convert flow: 2.5 MGD = 2,500,000
gal/day. Detention time = 500,000 gal / 2,500,000 gal/day = 0.2 days. Convert to
,hours: 0.2 days × 24 hr/day = 4.8 hours. Proper detention time ensures adequate
solids settling.
6: What is the primary function of a bar screen in wastewater treatment?
A. To remove dissolved metals
B. To remove large debris like rags, sticks, and plastics
C. To disinfect incoming wastewater
D. To adjust pH of influent
CORRECT ANSWER: B. To remove large debris like rags, sticks, and plastics
Rationale: Bar screens (coarse screens) are the first unit process, removing large
solids that could damage pumps, clog pipes, or interfere with downstream
processes. Fine screens remove smaller particles; dissolved metals require
chemical treatment; disinfection occurs later.
7: Which parameter is used to measure the concentration of suspended solids in
wastewater?
A. BOD
B. TSS (Total Suspended Solids)
C. COD
D. pH
CORRECT ANSWER: B. TSS (Total Suspended Solids)
Rationale: TSS measures the dry weight of particles retained on a filter (typically
0.45-2.0 µm pore size), expressed in mg/L. It quantifies settleable and non-settleable
suspended matter. BOD measures oxygen demand from organic matter; COD
measures chemical oxygen demand; pH measures acidity/alkalinity.
8: What is the recommended pH range for optimal coagulation with alum in
phosphorus removal?
A. 4.0–5.5
B. 5.5–7.0
, C. 7.0–8.5
D. 8.5–10.0
CORRECT ANSWER: B. 5.5–7.0
Rationale: Alum coagulation is most effective in the pH range 5.5–7.0, where
aluminum hydroxide floc forms optimally to adsorb and precipitate phosphate.
Outside this range, floc formation is poor, reducing phosphorus removal efficiency.
pH adjustment may be needed before/after coagulation.
9: Which South Carolina agency regulates wastewater treatment plant permits and
effluent limits?
A. South Carolina Department of Labor
B. South Carolina Department of Health and Environmental Control (SC DHEC)
C. South Carolina Water Resources Commission
D. U.S. Environmental Protection Agency (EPA) Region 4 only
CORRECT ANSWER: B. South Carolina Department of Health and Environmental
Control (SC DHEC)
Rationale: SC DHEC administers the National Pollutant Discharge Elimination System
(NPDES) permit program in South Carolina under delegation from EPA. It issues
permits, sets effluent limits, conducts inspections, and enforces compliance for
wastewater facilities.
10: What is the purpose of a grit chamber in wastewater treatment?
A. To remove organic matter through biological processes
B. To remove sand, gravel, and other heavy inorganic solids
C. To disinfect wastewater before secondary treatment
D. To add chemicals for phosphorus removal
CORRECT ANSWER: B. To remove sand, gravel, and other heavy inorganic solids
Rationale: Grit chambers use controlled flow velocity (about 1 ft/s) to allow heavy
inorganic solids (grit) to settle while keeping lighter organic solids suspended.
