Wastewater Treatment Operator Certification Practice Test

Which measurement is used to determine the amount of microorganisms present in the aeration tank?

1. Mixed Liquor Suspended Solids (MLSS)

2. Influent TSS

3. BOD

4. Mixed Liquor Volatile Suspended Solids (MLVSS)

The correct answer is: Mixed Liquor Volatile Suspended Solids (MLVSS)

The measurement used to determine the amount of microorganisms present in the aeration tank is Mixed Liquor Volatile Suspended Solids (MLVSS). This parameter specifically focuses on the portion of suspended solids in the mixed liquor that are organic and, more importantly, indicative of the microbial population actively processing the wastewater. MLVSS is crucial for assessing the biological treatment process because it reflects the concentration of living microorganisms that are responsible for the degradation of organic matter in the wastewater. A high MLVSS value typically indicates a robust microbial community that can efficiently carry out the treatment processes, while lower values may suggest poorer microbial health or efficiency. In contrast, Mixed Liquor Suspended Solids (MLSS) includes both volatile and non-volatile solids, which means it accounts for all suspended solids, not just those that are indicative of microbial life. Influent Total Suspended Solids (TSS) measures the amount of solids coming into the treatment system but does not specifically reflect the microbial population within the aeration tank. Biological Oxygen Demand (BOD) is useful for gauging the organic matter decomposition potential of wastewater, but it is not a direct measurement of microorganisms present in the system. Thus, MLVSS is the appropriate choice for determining the