Tennessee Wastewater Operator Practice Exam

What is a key advantage of operating two digesters in series instead of in parallel?

1. Increased energy efficiency

2. Higher total treatment capacity

3. Reduced likelihood of pathogen pass through

4. Improved mixing of digester contents

The correct answer is: Reduced likelihood of pathogen pass through

Operating two digesters in series offers the key advantage of reduced likelihood of pathogen pass-through. In a series configuration, the effluent from the first digester is fed into the second. This arrangement allows for a more thorough treatment process as pathogens that may survive the initial digestion phase in the first digester are subjected to additional time and conditions in the second digester. This extended exposure generally leads to better pathogen reduction, enhancing the overall safety and compliance of the treated effluent before it is released or further processed. This contrasts with other configurations, such as parallel operations, where both digesters operate independently. In that case, untreated or partially treated effluent can bypass one digester at a time, which might lead to a higher probability of pathogens escaping into the environment. Thus, the series operation effectively bolsters the reliability of the pathogen removal process, ensuring adherence to health and safety regulations.