Tennessee Wastewater Operator Practice Exam

A SOUR result of 0.87 mg/L DO/g TS/hr in an aerobic digester indicates what?

1. Solids are unprocessed

2. Solids are stabilized

3. Solids are overly saturated

4. Solids are decomposing rapidly

The correct answer is: Solids are stabilized

A SOUR result, or Specific Oxygen Uptake Rate, of 0.87 mg/L DO/g TS/hr in an aerobic digester serves as a significant indicator of the biological activity within the system. A value around this range suggests that the solids are being effectively stabilized. Stabilization refers to the process where organic materials are broken down by microorganisms, diminishing the overall biodegradability of the solids. The relatively low SOUR value indicates that the solids have undergone substantial processing, leading to reduced activity levels from the microorganisms, which is typically a sign of successful stabilization. If the solids were unprocessed or undergoing rapid decomposition, the SOUR values would likely be higher as more organic matter would be available for microbial consumption, reflecting vigorous biological activity. Overly saturated solids do not correlate directly with the SOUR measurement, as that would pertain more to the physical characteristics of the sludge rather than its biological state. Thus, a SOUR of 0.87 mg/L DO/g TS/hr clearly points toward a stabilized state of the solids in the aerobic digester.