Dive into the 2025 NY Wastewater Exam – Flush Away the Competition with Confidence!

When an anaerobic digester is described as "sour," it indicates that the environment has become acidic, often due to an accumulation of volatile fatty acids (VFAs) and a decrease in the pH level. This condition can inhibit the activity of methane-producing bacteria, which are essential for breaking down organic material and producing biogas.

Adding a basic substance, such as sodium bicarbonate or lime, helps to neutralize the acidity within the digester. This adjustment raises the pH to a more favorable level, promoting an optimal environment for the microorganisms that are responsible for the anaerobic digestion process. Maintaining a stable pH is crucial for the efficient functioning of the digester and the overall effectiveness of the wastewater treatment process.

In contrast, the other actions—such as increasing temperature, introducing more waste, or reducing digester volume—do not directly address the issue of acidity and may further complicate the situation. Increasing temperature might not stabilize pH levels, adding more waste could exacerbate the accumulation of VFAs, and reducing digester volume does not correct for the pH imbalance. Therefore, adding a basic substance is recognized as the most effective approach to rectify a sour anaerobic digester.