Wastewater New York State Practice Exam

What is one potential consequence of low dissolved oxygen in a biological reactor?

1. Improved effluent quality

2. Sludge bulking

3. Efficacy of nitrification

4. Reduced operational costs

The correct answer is: Sludge bulking

Low dissolved oxygen in a biological reactor can lead to sludge bulking, which is characterized by the accumulation of excess biomass that settles poorly. In aerobic treatment processes, microorganisms require sufficient dissolved oxygen to break down organic matter effectively. When oxygen levels are inadequate, the metabolic activity of these microorganisms is hindered, disrupting the process of digestion and leading to suboptimal conditions for settling. As a result, the biomass that does form may become less flocculent and more filamentous, causing it to resist settling during the secondary clarifier stages. This not only results in poor effluent clarity but can also require increased operational efforts to manage the bulking sludge. Monitoring and maintaining adequate levels of dissolved oxygen are critical for achieving good settling properties in biological treatment systems and ensuring the overall efficiency of the wastewater treatment process.