Tennessee Wastewater Operator Practice Exam

What should be reduced gradually when planning to take an anaerobic digester offline?

1. Temperature

2. Volatile solids loading

3. Feed rate

4. Microbial population

The correct answer is: Volatile solids loading

When planning to take an anaerobic digester offline, it is crucial to reduce the volatile solids loading gradually. This is important because volatile solids represent the organic matter in the digester that microorganisms utilize for digestion, producing biogas as a byproduct. By reducing the volatile solids loading slowly, the microbial ecosystem within the digester can adjust to the decrease in available organic material, thus maintaining stability. If volatile solids are reduced too quickly, it can lead to a disruption in the microbial population dynamics, potentially causing issues such as decreased gas production or destabilization of the digestion process. This gradual approach helps minimize shock to the system, ensuring that the microorganisms can adjust and continue to operate effectively for as long as possible before the digester is fully taken offline. Other factors like temperature, feed rate, and microbial populations might play roles in digester function, but specifically reducing volatile solids loading is the key step in preparing for an orderly shutdown of the anaerobic digestion process.