Tennessee Wastewater Operator Practice Exam

To ensure adequate volatile solids destruction, what should the DO concentration in a digester be?

1. At least 0.5 mg/L

2. At least 1.0 mg/L

3. At least 2.0 mg/L

4. At least 3.0 mg/L

The correct answer is: At least 1.0 mg/L

The concentration of dissolved oxygen (DO) in a digester is critical for ensuring adequate volatile solids destruction, as it influences the metabolic activity of microorganisms involved in the digestion process. A DO concentration of at least 1.0 mg/L is necessary to support the aerobic digestion microorganisms without inhibiting their activity. Microorganisms in the digester need a sufficient oxygen supply to efficiently break down volatile solids. At lower oxygen levels, the microbial activity may diminish, leading to reduced digestion efficiency and potentially incomplete breakdown of organic matter. A concentration lower than 1.0 mg/L could contribute to anaerobic conditions and a shift in microbial populations, ultimately affecting the digestion process adversely. Higher DO levels, such as 2.0 mg/L or more, can lead to excessive aeration, which is generally not required in anaerobic digestion processes, where lower oxygen levels are preferable for the growth of anaerobic bacteria. Thus, maintaining a balance is essential, making 1.0 mg/L the critical minimum to ensure that sufficient microbial activity occurs to degrade the volatile solids effectively.