Wastewater Operator Wastewater Laboratory Procedures Questions and Answers

Question 1

An operator is preparing to measure the pH of a raw influent sample. According to standard laboratory practice, which of the following describes the correct procedure for calibrating a pH meter?

Accepted Answer

Rinse the probe with deionized water, calibrate with a pH 7.0 buffer, rinse again, then calibrate with a second buffer (e.g., pH 4.0 or 10.0).

Answer

Calibrate using a single buffer solution closest to the expected sample pH.

Answer

Rinse the probe with tap water, calibrate with pH 7.0 buffer, then measure the sample.

Answer

Immerse the probe in the sample first to acclimate it, then perform a two-point calibration.

Question 2

When performing a 5-day Biochemical Oxygen Demand (BOD₅) test, what is the primary reason for incubating the sample bottles in complete darkness at 20°C?

Accepted Answer

To inhibit algae growth, which would produce oxygen through photosynthesis and interfere with the results.

Answer

To prevent the growth of anaerobic bacteria which would consume organic matter too quickly.

Answer

To accelerate the chemical oxidation of inorganic compounds in the sample.

Answer

To maintain a constant pressure inside the sealed BOD bottle.

Question 3

An operator is performing a Total Suspended Solids (TSS) analysis. After filtering a known volume of sample, the glass-fiber filter is placed in a drying oven. What is the standard temperature for drying the TSS filter?

Accepted Answer

103°C to 105°C

Answer

550°C ± 50°C

Answer

20°C ± 1°C

Answer

180°C ± 2°C

Question 4

During a fecal coliform test using the membrane filtration method, the operator places the membrane filter onto the culture medium in the petri dish. Which of the following is a critical step in this process?

Accepted Answer

Rolling the filter onto the medium to avoid trapping air bubbles between the filter and the agar.

Answer

Placing the filter grid-side down to ensure direct contact with the medium.

Answer

Exposing the plate to UV light for 30 seconds to sterilize the surface before incubation.

Answer

Adding a few drops of the sample water on top of the filter after placement to ensure it is moist.

Question 5

A laboratory is implementing a Quality Assurance/Quality Control (QA/QC) program. Which of the following is an example of a Quality Control (QC) activity?

Accepted Answer

Analyzing a laboratory-fortified blank (LFB) with each batch of samples.

Answer

Writing a Standard Operating Procedure (SOP) for a new analytical method.

Answer

Analyzing a proficiency testing (PT) sample from an external provider.

Answer

Calibrating all laboratory thermometers annually against a NIST-certified thermometer.

Question 6

When using the Winkler titration method to determine dissolved oxygen, a series of reagents are added to the sample in the field to 'fix' the oxygen. What is the purpose of this 'fixing' step?

Accepted Answer

To precipitate the dissolved oxygen into a visible floc, which is later dissolved and titrated.

Answer

To calibrate the titration equipment before analysis.

Answer

To adjust the sample pH to exactly 7.0 before transporting it to the lab.

Answer

To remove any chlorine residual that would interfere with the titration.