Basic Wastewater Operator Practice Exam

What would be the operator's first indicator when a high organic waste load reaches an activated sludge plant?

1. Decrease in the dissolved oxygen, D.O. residual in the reactors aeration tanks

2. A call from the industry discharging the waste

3. Purple water at the influent

4. Green water at the influent

The correct answer is: Decrease in the dissolved oxygen, D.O. residual in the reactors aeration tanks

The primary indicator of a high organic waste load in an activated sludge plant is a decrease in the dissolved oxygen (D.O.) residual in the aeration tanks. When organic waste increases, it tends to consume more oxygen as microorganisms break down the organic material. This increased biological activity depletes the oxygen that is available for both the microorganisms and the overall health of the wastewater treatment process. Monitoring the D.O. levels is crucial for operators because maintaining adequate oxygen levels is essential for the aerobic bacteria responsible for the breakdown of organic matter. A sudden drop in D.O. can signal overloading, which not only affects treatment performance but could also lead to unsatisfactory effluent quality and operational problems such as the potential for anaerobic conditions, which can produce undesirable odors and other byproducts. In contrast, the other options may indicate issues but are not direct or immediate indicators of a high organic load. A call from the industry discharging waste might occur later as a response to operational issues, while the presence of discolored water, such as purple or green, does not specifically indicate a high organic load but could relate to other factors like algae blooms or the presence of certain chemicals or pollutants.