Tennessee Wastewater Operator Practice Exam

Under what condition do aerobic digesters meet the definition of PSRPP?

1. Temperature is maintained at 15°C

2. SRT is at least 30 days

3. SRT is at least 40 days at 20°C

4. pH levels are above 7.5

The correct answer is: SRT is at least 40 days at 20°C

The condition that aerobic digesters meet the definition of PSRPP (Primary Sludge Removal and Proper Processing) is related to the SRT (Solid Retention Time) and temperature levels necessary for effective microbial activity. When the SRT is at least 40 days at 20°C, it ensures that the microorganisms have sufficient retention time to break down organic matter in the sludge effectively. This longer SRT promotes stabilization of the sludge and enhances the reduction of volatile solids, which is essential for meeting the PSRPP criteria. Maintaining an adequate SRT is crucial because it correlates directly with the efficiency of the digestion process, allowing microbes to thrive and perform their function over a sufficient duration. At 20°C, this temperature is typical for many biological processes, and higher SRT values help in achieving a more thorough digestion of the organic material present in the sludge. Other choices do not provide the required conditions to meet PSRPP. For instance, maintaining a temperature of 15°C, while it may support some biological activity, does not encompass all conditions necessary for full stabilization compared to the 20°C requirement. Additionally, an SRT of at least 30 days is shorter than what is required, and while pH levels above 7