California Wastewater Treatment Operator Practice Exam

What will happen if too much raw sludge is added to the digester?

1. Accelerates the digestion process

2. Increases biogas production

3. Acid fermenters will predominate and lower the pH

4. Causes foaming issues

The correct answer is: Acid fermenters will predominate and lower the pH

When too much raw sludge is added to the digester, the dynamics within the digestion process can shift significantly. Excessive raw sludge contributes to higher concentrations of organic matter, which can lead to a predominance of acid-forming bacteria. This shift can result in the production of organic acids, which subsequently lowers the pH of the digester environment. Under normal conditions, a balanced pH is crucial for the optimal functioning of the microbial communities involved in anaerobic digestion. An acidic environment, caused by an overload of raw sludge and the consequent rapid fermentation by acidogenic bacteria, can inhibit the activity of methanogenic bacteria that are essential for biogas production. This detrimental effect on the pH can impair the digestion process overall, leading to reduced efficiency and potential operational challenges. Inadequate pH balance is critical to maintain because it enables a healthy ecosystem for the microbes involved in breaking down the sludge. Hence, excessive raw sludge can lead to unfavorable conditions marked by an increase in acid levels, heavily impacting the digestion process.