Basic Wastewater Operator Practice Exam

What is the purpose of heating and mixing a primary anaerobic digester?

1. To slow down the digestion rate

2. To increase the digestion rate

3. To allow for more room in the digester

4. To increase effluent quality

The correct answer is: To increase the digestion rate

The purpose of heating and mixing a primary anaerobic digester is to increase the digestion rate. In anaerobic digestion, microorganisms break down organic matter in the absence of oxygen, producing biogas as a byproduct. By heating the digester, the temperature can be optimized to maintain an ideal environment for these microorganisms, as they thrive at specific temperature ranges. Warmer temperatures promote microbial activity, leading to more effective decomposition of waste and faster production of biogas. Mixing the contents of the digester also plays a crucial role. It helps distribute heat evenly, prevents the formation of scum or sediment layers, and ensures that all waste materials are in contact with the microorganisms. This agitation enhances the overall efficiency of the digestion process, resulting in a quicker breakdown of organic material. While the other options focus on different outcomes, they do not align with the primary objective of heating and mixing in a digester system, which is to optimize conditions for microbial activity and thus enhance the digestion rate.