Texas Wastewater Class B Practice Exam

Under what conditions does old sludge quality settle?

1. Gently and Uniformly over 5 minutes

2. Rapidly and Ragged over 5 minutes

3. Gently and Uniformly over 15 to 20 minutes

4. Rapidly and Uniformly over 15 to 20 minutes

The correct answer is: Rapidly and Ragged over 5 minutes

The correct description of how old sludge quality settles is characterized as settling rapidly and raggedly over a period of time. When referring to "old sludge," this typically indicates that the sludge has been subjected to anaerobic or prolonged conditions, which can lead to a less compact structure. As a result, during the settling process, the particles tend to spread out unevenly, creating a ragged appearance as they drop out of suspension. Old sludge often contains larger and more varied particles, which do not settle uniformly. This non-uniformity is a sign of poor quality sludge that has lost some of its desirable settling characteristics. The rapid settling indicates that these particles may fall quickly due to their weight, yet the inconsistency in settling leads to an uneven distribution at the bottom of the tank. In contrast, options that suggest a gentle or uniform settling phase do not align with the commonly observed behavior of old sludge, which is known for its turmoil and disorganization as it settles. Thus, the identification of rapid and ragged settling reflects the reality of the sludge's condition and behavior in a treatment process.