Tennessee Wastewater Operator Practice Exam

What indicates an increase in effluent ammonia concentrations in activated sludge treatment?

1. Increased treatment effectiveness

2. Return of supernatant from anaerobic digestion

3. Higher aeration rates

4. Reduced sludge blanket

The correct answer is: Return of supernatant from anaerobic digestion

The presence of increased effluent ammonia concentrations in activated sludge treatment is often associated with the return of supernatant from anaerobic digestion. This is primarily due to the breakdown of organic matter during anaerobic conditions, which can result in the release of ammonia as the nitrogenous components are decomposed. When supernatant from anaerobic digestion is returned to the treatment process, it contains dissolved ammonia and other nitrogen compounds that can elevate the levels of ammonia in the effluent. This return can disrupt the balance of the activated sludge process where ammonia would typically be processed by nitrification. Understanding the significance of supernatant return highlights the broader implications for wastewater treatment systems, particularly how operational decisions such as recycling digestate can influence effluent quality and nitrogen management within the treatment plant.