Free WW Laboratory Analysis Procedures and Quality Control Questions and Answers

Question 1

What is the standard incubation temperature and duration for the BOD5 test?

Accepted Answer

20°C for 5 days

Answer

The Biochemical Oxygen Demand (BOD5) test measures the amount of oxygen consumed by microorganisms over a five-day period. To ensure consistent and comparable results, the standard method specifies an incubation temperature of 20°C for 5 days in the absence of light.

Question 2

When is a 'grab sample' more appropriate than a 'composite sample'?

Accepted Answer

When measuring pH and chlorine residual

Answer

A grab sample is a single sample collected at a specific time and place, representing conditions only at that moment. It is used for parameters that can change rapidly, such as pH, dissolved oxygen, or chlorine residual. A composite sample, collected over time, would average these values and mask any fluctuations.

Question 3

In laboratory quality control, what is the purpose of analyzing a 'blank'?

Accepted Answer

To check for contamination of reagents or equipment

Answer

A blank is a sample of distilled or deionized water that is treated exactly like a wastewater sample. Its purpose is to check for contamination in the reagents, glassware, or analytical instruments. An ideal blank should yield a result of zero or below the detection limit.

Question 4

The procedure for Total Suspended Solids (TSS) requires filtering a sample through what?

Accepted Answer

A pre-weighed glass-fiber filter

Answer

The TSS test measures the total amount of solid material that is not dissolved in a sample. The standard method involves filtering a known volume of water through a pre-weighed glass-fiber filter paper with a specific pore size, typically 1.5 micrometers. The filter is then dried and weighed again to determine the mass of the captured solids.

Question 5

How often should a pH meter be calibrated?

Accepted Answer

Daily, before use

Answer

A pH meter's electrode can drift over time, leading to inaccurate readings. To ensure accuracy, it must be calibrated regularly using standard buffer solutions. Best practice, and a requirement for many regulated labs, is to calibrate the meter at the beginning of each day or before each set of measurements.

Wastewater Operator Certification Practice Test

Wastewater Operator Certification Practice Test

Free WW Laboratory Analysis Procedures and Quality Control Questions and Answers