Tennessee Wastewater Operator Practice Exam

What is injected into the anaerobic digester liquid to create mixing currents?

1. Water

2. Biogas

3. Sludge

4. Air

The correct answer is: Biogas

Injecting biogas into the anaerobic digester liquid generates mixing currents essential for the effective operation of the digester. Biogas is produced during the anaerobic digestion process as microorganisms break down organic materials in the absence of oxygen. By introducing biogas into the liquid, bubbles are created that rise to the surface. This movement helps circulate the contents of the digester, promoting further interaction between the microorganisms and the organic material. Proper mixing enhances the overall efficiency of the anaerobic digestion process, ensuring that solid particles are suspended and evenly distributed, which leads to improved digestion rates and better biogas production. Using other substances, such as water, sludge, or air, would not provide the same effective mixing. Water could dilute the contents, while adding air would introduce oxygen, which is counterproductive to anaerobic digestion. Similarly, while sludge is an integral part of the process, it does not create mixing currents like biogas does.