ABC Wastewater Treatment Operator Level 3
Certification Exam – Wastewater Treatment Plant
Laboratory Analysis Practice Questions, Answers &
Detailed Explanations | 2026 Updated Edition
Question 1
To have significant meaning for laboratory tests of the evaluation of a wastewater
treatment plant's performance the best method of sampling is
A. Grab sampling
B. Hourly sampling
C. Sampling during peak flow
D. Proportional composite sampling
E. Automatic sampling
Correct Answer: D
Explanation: To evaluate plant performance, you need a sample that represents the
average wastewater composition over time. Flow-proportional composite sampling,
which collects sub-samples in proportion to the flow, is the only way to achieve this and
is considered the preferable method for routine monitoring.
Question 2
BOD samples should be collected before chlorination because
A. Chlorine reacts with the buffer solution
B. Chlorine interferes with the activity of organisms
C. Chlorine reacts with the calcium ions
D. Chlorine affects the alkalinity
Correct Answer: B
Explanation: Chlorine is a disinfectant and is toxic to the microorganisms that need to
consume the organic matter during the 5-day BOD incubation. Therefore, samples must
be collected and dechlorinated before the test to ensure an accurate result.
Question 3
A water sample is "fixed" in the field by
A. Keeping the sample in a Cipolletti device
B. Anchoring the container to the stream bed
pg. 1
,C. Adding chemicals to prevent the changing of water quality
D. Maintaining a constant sample temperature of 95°F
Correct Answer: C
Explanation: In water and wastewater analysis, "fixing" a sample means adding
specific reagents to prevent biological or chemical changes that would alter the
measurement of a particular parameter (like dissolved oxygen) before the sample can be
analyzed in the lab.
Question 4
The best procedure for determining the SS of a plant effluent is to analyze
A. A 24-hr composite sample of the effluent
B. A grab sample of the effluent at high flow
C. A grab sample of the effluent at low flow
D. A series of grab samples taken at different times during the day
Correct Answer: A
Explanation: For regulatory compliance and accurate performance assessment, a 24-
hour composite sample is required for parameters like Total Suspended Solids (TSS). A
single grab sample is not representative of the plant's overall performance.
Question 5
A sample obtained by taking portions of wastewater at a collection point in proportion
to the flow is called
A. A most probable number (MPN)
B. A weighted composite
C. A routine sample
D. A bacterial-solids sample
Correct Answer: B
Explanation: A weighted composite, also known as a flow-proportional composite, is a
sample created by mixing portions of wastewater in proportion to the flow rate at the
time of collection. This results in an average sample that accurately represents the total
pollutant load.
Question 6
Settleable solids by volume are determined through the use of
A. A Nessler tube
B. A Kjeldahl flask
pg. 2
,C. A Gooch crucible
D. An Imhoff cone
Correct Answer: D
Explanation: Settleable solids are measured by volume using an Imhoff cone. The
sample is allowed to settle in the cone for 45 minutes, and the volume of settled solids is
read directly from the graduated scale on the cone.
Question 7
The settleable solids test is primarily used to
A. Measure the volume of solids that may be removed by settling tanks
B. Determine the BOD required for treatment
C. Measure the rate of decomposition of organic volatile solids
D. Determine the amount of chlorine required
Correct Answer: A
Explanation: The settleable solids test is a simple indicator of the amount of solids
that will naturally sink and can be removed by gravity in primary clarifiers and other
settling basins. It helps in process control.
Question 8
The standard total SS test requires the Gooch crucible fiber glass mat and solids to be
dried in the oven at
A. 95°C
B. 103°C
C. 110°C
D. 115.5°C
Correct Answer: B
Explanation: The standard method for determining Total Suspended Solids (TSS)
dictates that the filter and retained solids must be dried in an oven at 103°C to 105°C to
remove all moisture and provide a consistent measurement.
Question 9
The SS content of wastewater is most accurately measured by
A. Filtering the sample through a specially prepared filter; drying the filter and material
retained on it in an oven
B. Centrifuging the sample and measuring the volume of solids
pg. 3
, C. Evaporating the sample and weighing the residue
D. Measuring the turbidity of the sample
Correct Answer: A
Explanation: The TSS test is a gravimetric method. A well-mixed sample is filtered,
and the filter with the captured solids is dried to a constant weight. The increase in
weight is the mass of suspended solids.
Question 10
The amount of sample to be used in determining SS depends on the sample
A. Amount of grease in the sample
B. Amount of SS in the sample
C. Degree of turbidity of the sample
D. Type of vacuum apparatus available
Correct Answer: B
Explanation: The volume of sample to filter depends on the concentration of
suspended solids. Using too little or too much sample can make the test inaccurate or
impractical. The goal is to collect between 2.5 and 200 mg of solids for an accurate
measurement.
Question 11
The advantage of the centrifuge test for SS determination in comparison with the other
method is
A. Accuracy of results
B. Large volume of sample it can handle
C. Low cost
D. Speed of answer
Correct Answer: D
Explanation: The centrifuge method is a rapid, field-friendly alternative to the
standard gravimetric TSS test. While it is fast, it is known to be less accurate than the
official oven-drying method.
Question 12
The following indicator is most useful in determining pH values near neutrality:
A. Bromthymol blue
B. Bromcresol green
pg. 4
Certification Exam – Wastewater Treatment Plant
Laboratory Analysis Practice Questions, Answers &
Detailed Explanations | 2026 Updated Edition
Question 1
To have significant meaning for laboratory tests of the evaluation of a wastewater
treatment plant's performance the best method of sampling is
A. Grab sampling
B. Hourly sampling
C. Sampling during peak flow
D. Proportional composite sampling
E. Automatic sampling
Correct Answer: D
Explanation: To evaluate plant performance, you need a sample that represents the
average wastewater composition over time. Flow-proportional composite sampling,
which collects sub-samples in proportion to the flow, is the only way to achieve this and
is considered the preferable method for routine monitoring.
Question 2
BOD samples should be collected before chlorination because
A. Chlorine reacts with the buffer solution
B. Chlorine interferes with the activity of organisms
C. Chlorine reacts with the calcium ions
D. Chlorine affects the alkalinity
Correct Answer: B
Explanation: Chlorine is a disinfectant and is toxic to the microorganisms that need to
consume the organic matter during the 5-day BOD incubation. Therefore, samples must
be collected and dechlorinated before the test to ensure an accurate result.
Question 3
A water sample is "fixed" in the field by
A. Keeping the sample in a Cipolletti device
B. Anchoring the container to the stream bed
pg. 1
,C. Adding chemicals to prevent the changing of water quality
D. Maintaining a constant sample temperature of 95°F
Correct Answer: C
Explanation: In water and wastewater analysis, "fixing" a sample means adding
specific reagents to prevent biological or chemical changes that would alter the
measurement of a particular parameter (like dissolved oxygen) before the sample can be
analyzed in the lab.
Question 4
The best procedure for determining the SS of a plant effluent is to analyze
A. A 24-hr composite sample of the effluent
B. A grab sample of the effluent at high flow
C. A grab sample of the effluent at low flow
D. A series of grab samples taken at different times during the day
Correct Answer: A
Explanation: For regulatory compliance and accurate performance assessment, a 24-
hour composite sample is required for parameters like Total Suspended Solids (TSS). A
single grab sample is not representative of the plant's overall performance.
Question 5
A sample obtained by taking portions of wastewater at a collection point in proportion
to the flow is called
A. A most probable number (MPN)
B. A weighted composite
C. A routine sample
D. A bacterial-solids sample
Correct Answer: B
Explanation: A weighted composite, also known as a flow-proportional composite, is a
sample created by mixing portions of wastewater in proportion to the flow rate at the
time of collection. This results in an average sample that accurately represents the total
pollutant load.
Question 6
Settleable solids by volume are determined through the use of
A. A Nessler tube
B. A Kjeldahl flask
pg. 2
,C. A Gooch crucible
D. An Imhoff cone
Correct Answer: D
Explanation: Settleable solids are measured by volume using an Imhoff cone. The
sample is allowed to settle in the cone for 45 minutes, and the volume of settled solids is
read directly from the graduated scale on the cone.
Question 7
The settleable solids test is primarily used to
A. Measure the volume of solids that may be removed by settling tanks
B. Determine the BOD required for treatment
C. Measure the rate of decomposition of organic volatile solids
D. Determine the amount of chlorine required
Correct Answer: A
Explanation: The settleable solids test is a simple indicator of the amount of solids
that will naturally sink and can be removed by gravity in primary clarifiers and other
settling basins. It helps in process control.
Question 8
The standard total SS test requires the Gooch crucible fiber glass mat and solids to be
dried in the oven at
A. 95°C
B. 103°C
C. 110°C
D. 115.5°C
Correct Answer: B
Explanation: The standard method for determining Total Suspended Solids (TSS)
dictates that the filter and retained solids must be dried in an oven at 103°C to 105°C to
remove all moisture and provide a consistent measurement.
Question 9
The SS content of wastewater is most accurately measured by
A. Filtering the sample through a specially prepared filter; drying the filter and material
retained on it in an oven
B. Centrifuging the sample and measuring the volume of solids
pg. 3
, C. Evaporating the sample and weighing the residue
D. Measuring the turbidity of the sample
Correct Answer: A
Explanation: The TSS test is a gravimetric method. A well-mixed sample is filtered,
and the filter with the captured solids is dried to a constant weight. The increase in
weight is the mass of suspended solids.
Question 10
The amount of sample to be used in determining SS depends on the sample
A. Amount of grease in the sample
B. Amount of SS in the sample
C. Degree of turbidity of the sample
D. Type of vacuum apparatus available
Correct Answer: B
Explanation: The volume of sample to filter depends on the concentration of
suspended solids. Using too little or too much sample can make the test inaccurate or
impractical. The goal is to collect between 2.5 and 200 mg of solids for an accurate
measurement.
Question 11
The advantage of the centrifuge test for SS determination in comparison with the other
method is
A. Accuracy of results
B. Large volume of sample it can handle
C. Low cost
D. Speed of answer
Correct Answer: D
Explanation: The centrifuge method is a rapid, field-friendly alternative to the
standard gravimetric TSS test. While it is fast, it is known to be less accurate than the
official oven-drying method.
Question 12
The following indicator is most useful in determining pH values near neutrality:
A. Bromthymol blue
B. Bromcresol green
pg. 4
