Basic Wastewater Operator Practice Exam

What is the predominant organism in a healthy activated sludge treatment plant?

1. Stalked ciliates

2. Rotifers

3. Nematodes

4. Amoebas

The correct answer is: Stalked ciliates

In a healthy activated sludge treatment plant, the predominant organism is stalked ciliates. These microorganisms play a crucial role in the wastewater treatment process by consuming bacteria and organic matter, which helps maintain the balance and efficiency of the activated sludge system. Stalked ciliates are efficient grazers and contribute to the floc formation process, which is essential for the settling of sludge. Their presence indicates a well-functioning treatment plant, as they thrive in conditions that suggest adequate aeration and a balanced microbial community. While rotifers, nematodes, and amoebas may also be present in activated sludge systems, they do not dominate in the same way as stalked ciliates. Rotifers, for example, are generally considered indicators of advanced treatment conditions but are not as critical to the primary actions of the activated sludge process. Nematodes and amoebas can indicate varying degrees of biological conditions but are not as essential as stalked ciliates for the overall microbial health and performance of the system. Therefore, the presence of stalked ciliates signifies a healthy balance of microbial activity in the treatment process.