Tennessee Wastewater Operator Practice Exam

Why are MLVSS used for OUR and SOUR tests instead of MLSS?

1. MLSS is easier to measure

2. MLVSS measures live organisms

3. MLVSS is less variable

4. MLSS is only for chemical analysis

The correct answer is: MLVSS measures live organisms

Using MLVSS (Mixed Liquor Volatile Suspended Solids) for OUR (Oxygen Uptake Rate) and SOUR (Specific Oxygen Uptake Rate) tests is preferred because MLVSS specifically targets the live microorganisms present in the mixed liquor of a wastewater treatment process. This focus is crucial because both OUR and SOUR measurements are indicators of the biological activity and health of the microbial population responsible for breaking down organic material in the wastewater. In contrast, MLSS (Mixed Liquor Suspended Solids) includes both living biomass and inert solids, which do not contribute to the biological process. Therefore, measuring MLSS can give a skewed view of the microbial activity because it combines the mass of active microorganisms with that of dead or non-active solids. In wastewater treatment, the primary concern is understanding how effectively the living organisms are treating the water, making MLVSS a more accurate reflection of the active biomass available for biodegradation processes. The biological processes of wastewater treatment rely on the activity of living organisms, which is encapsulated in the MLVSS measurement. Consequently, utilizing MLVSS in these tests offers a clearer picture of the system's operational efficiency and the health of the microbial community, allowing for more informed decisions in managing treatment processes.