Tennessee Wastewater Operator Practice Exam

Why is thermal hydrolysis added before anaerobic digestion?

1. To increase sludge volume

2. To increase the rate of digestion

3. To stabilize the end product

4. To reduce processing time

The correct answer is: To increase the rate of digestion

Thermal hydrolysis is a process that involves applying heat and pressure to wastewater sludge before anaerobic digestion. This pre-treatment serves to break down complex organic materials in the sludge, making them more accessible for microbial digestion. The primary benefit of this process is that it significantly increases the rate at which microorganisms can digest the organic matter present in the sludge. By breaking down cell structures, thermal hydrolysis releases intracellular materials that are easier for the anaerobic bacteria to access and consume. This leads to a faster breakdown of the organic material contained within the sludge, thus enhancing the overall efficiency of the anaerobic digestion process. Consequently, thermal hydrolysis not only accelerates the digestion process but can also improve the biogas yield, providing more energy recovery from the digestion process. In summary, the primary role of thermal hydrolysis before anaerobic digestion is to increase the rate of digestion by making the organic material more readily available for microbial action, aligning it well with the correct answer choice.