Wastewater New York State Practice Exam

What is the best way to feed an anaerobic digester?

1. Large infrequent feed

2. Small, frequent feed, near continuous feed rate

3. Constant feed rate throughout the day

4. Only during peak times of digestion

The correct answer is: Small, frequent feed, near continuous feed rate

Feeding an anaerobic digester with a small, frequent, near-continuous feed rate is beneficial for several reasons. This method allows for a steady supply of organic material, which optimizes the biological processes occurring within the digester. Anaerobic digestion relies on microorganisms to break down the organic matter in the absence of oxygen, and these microorganisms thrive in a stable environment where they have a consistent supply of food. When feed is introduced in smaller, more frequent quantities, it reduces the chance of overloading the digester, which can lead to fluctuations in pH and other operational parameters that may disrupt the microbial community and result in decreased efficiency or even digester failure. A continuous feeding strategy helps maintain a more stable concentration of substrates, ensuring that the microorganisms have a constant source of nutrients to convert into biogas. Moreover, this approach enhances the overall hydraulic retention time and ensures that there is enough time for the biogas-producing bacteria to effectively process the organic matter. This stability in feeding not only maximizes biogas production but also helps avoid issues like scum formation and foam, which can occur with large and infrequent feed rates. In situations where feed is introduced only during peak times or intermittently, the digester may experience periods of nutrient