Tennessee Wastewater Operator Practice Exam

If the DO concentration in the activated sludge basin increases from 2 to 6 mg/l, what is the most likely cause?

1. Toxic material in the influent

2. Improved aeration efficiency

3. Increased temperature

4. High flow rate

The correct answer is: Toxic material in the influent

In this scenario, the increase in dissolved oxygen (DO) concentration in the activated sludge basin from 2 to 6 mg/l suggests a significant change in the biological conditions within the wastewater treatment process. An increase in DO typically indicates that more oxygen is being introduced or retained in the system, which is often a direct result of enhanced aeration. Improved aeration efficiency is indeed the most plausible explanation for the DO increase. When aeration is more effective, it allows for better oxygen transfer from the air to the wastewater, thereby raising the dissolved oxygen levels. This is crucial for the microbial populations in the activated sludge process, which require sufficient oxygen to effectively break down organic material and treat the wastewater. While toxic materials in the influent could potentially disrupt the biological processes, it is more likely that their presence would lead to a decrease in DO rather than an increase, as many toxic substances can inhibit microbial activity. Increased temperature can affect the solubility of oxygen and may enhance microbial activity, but it wouldn't directly cause such a significant increase in DO levels. Lastly, a high flow rate might dilute the activated sludge and contribute to lower concentrations of DO, as it can lead to a more rapid turnover of water and less time for oxygen transfer. Each of