Basic Wastewater Operator Practice Exam

If you notice a predominance of rotifers in your activated sludge sample while looking at it under a microscope, what does this indicate?

1. Healthy sludge

2. Young sludge

3. Old sludge

4. Middle age sludge

The correct answer is: Old sludge

The presence of a predominance of rotifers in an activated sludge sample typically indicates that the sludge is older. Rotifers are a type of microfauna that thrive in well-established biological systems, particularly in mature activated sludge. Their abundance suggests that the microbial community has stabilized and has a balanced ecosystem, characteristic of older sludge. In this context, healthy sludge can include a variety of microorganisms, but the presence of rotifers specifically leans towards an aged sludge scenario. Young sludge tends to be less diverse and may not yet support the type of complex life forms such as rotifers. Similarly, middle-aged sludge would show signs of some microbial stability but may not yet reach the level of diversity and complexity found in older sludge assemblages. Thus, the correct answer indicating the condition of the activated sludge sample aligns with the characteristics associated with older sludge due to the notable presence of rotifers.