Wastewater New York State Practice Exam

What type of samples should be taken for microscopic examination from an aeration tank?

1. Composite samples

2. Grab samples

3. Settled samples

4. Continuous flow samples

The correct answer is: Grab samples

For microscopic examination from an aeration tank, grab samples are the most appropriate choice because they provide a snapshot of the mixed liquor at a specific moment. This allows for an accurate analysis of the microorganisms present in the aeration tank at that particular time, which is essential for monitoring the health and functioning of the biological treatment process. Grab samples offer the advantage of capturing the variability in microbial populations that can occur throughout the day, particularly in systems where conditions may fluctuate due to changes in inflow or operational parameters. This method can effectively reflect the overall activity and distribution of microorganisms, such as bacteria and protozoa, which are crucial for the treatment of wastewater. Other sampling methods, such as composite samples, which average out the constituents over a period, may dilute specific populations that could be critical for understanding the system's performance at any given time. Settled samples primarily contain settled solids and may not represent the active biomass effectively. Continuous flow samples are generally used for process monitoring or chemical analysis rather than microbial assessment, making grab samples the most suitable choice in this context.