Tennessee Wastewater Operator Practice Exam

What can be an effect of low dissolved oxygen in an activated sludge process?

1. Decreased nitrification rates

2. Improved floc formation

3. Increased biomass growth

4. Enhanced organic degradation

The correct answer is: Decreased nitrification rates

In an activated sludge process, low dissolved oxygen can significantly impact the biological treatment of wastewater. The correct answer involves the decreased nitrification rates because nitrification is a biological process that requires oxygen. It involves the conversion of ammonia into nitrites and then into nitrates, which is carried out by specialized bacteria known as nitrifying bacteria. These bacteria require a sufficient amount of dissolved oxygen to thrive and perform their function effectively. When dissolved oxygen levels drop too low, these bacteria become less active, ultimately leading to a decrease in nitrification rates. This situation can affect the overall efficiency of the treatment process, as ammonia and other nitrogen compounds may not be adequately converted and removed from the wastewater, potentially resulting in higher nitrogen concentrations in the effluent. The other options, such as improved floc formation, increased biomass growth, and enhanced organic degradation, would typically be associated with optimal dissolved oxygen levels. Low dissolved oxygen, conversely, is likely to result in poorer floc formation, limited biomass growth, and inefficient degradation of organic matter, not enhancements. In summary, the presence of low dissolved oxygen directly disrupts the nitrification function in an activated sludge system, demonstrating the importance of maintaining proper oxygen levels in wastewater treatment processes.