Tennessee Wastewater Operator Practice Exam

Which observation indicates that proper mixing is occurring in the digester?

1. Low temperature readings

2. High gas production

3. Clear water at the surface

4. Visible agitation of sludge

The correct answer is: High gas production

High gas production is a strong indicator that proper mixing is occurring in the digester. This is because effective mixing ensures the substrates are evenly distributed throughout the digester, allowing for optimal interaction between the organic material and the microorganisms that facilitate anaerobic digestion. When these organisms are able to efficiently break down the organic matter, they produce biogas (mainly methane and carbon dioxide), which is indicative of successful digestion processes. When mixing is insufficient, organic material can settle and anaerobically decay, leading to lower gas production and reduced efficiency of the treatment process. Therefore, high gas production reflects not only the activity of the microorganisms but also the effectiveness of the mixing process in maintaining a well-distributed environment in the digester. Other indicators, like low temperature readings, clear water at the surface, or visible agitation of sludge, do not specifically denote the effectiveness of microbial activity in relation to the mixing process in the digester. While they might suggest certain aspects of the operation, they do not directly correlate with the digestion efficiency the way that high gas production does.