Laboratory Analysis Procedures and Quality Control Flashcards
7 cards from real Wastewater Operator Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Laboratory Analysis Procedures and Quality Control flashcards as text
What is the standard incubation temperature and duration for the BOD5 test?
Answer: 20°C for 5 days
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.
When is a 'grab sample' more appropriate than a 'composite sample'?
Answer: When measuring pH and chlorine residual
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.
In laboratory quality control, what is the purpose of analyzing a 'blank'?
Answer: To check for contamination of reagents or equipment
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.
The procedure for Total Suspended Solids (TSS) requires filtering a sample through what?
Answer: A pre-weighed glass-fiber filter
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.
How often should a pH meter be calibrated?
Answer: Daily, before use
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.
What is the holding time and preservation method for a sample that will be tested for fecal coliform?
Answer: Cool to <10°C, analyze within 8 hours
Bacterial populations in a sample can change rapidly after collection. To get an accurate count, fecal coliform samples must be analyzed as soon as possible. They should be cooled to <10°C and analyzed within 8 hours of collection.
A 'split sample' is sent to an external lab as part of a quality assurance program. What is the purpose of this?
Answer: To verify the accuracy of the in-house laboratory's results
A split sample is a single sample that is divided into two or more parts, with one part analyzed in-house and the other sent to an external, certified laboratory. Comparing the results helps to validate the accuracy of the in-house lab's procedures, equipment, and analyst technique. It is a common component of a Quality Assurance/Quality Control (QA/QC) program.