A large number of rotifers in a treatment system suggests which type of sludge?

The presence of a large number of rotifers in a treatment system typically indicates the presence of old sludge. Rotifers are microorganisms that thrive in environments with nutrient-rich, well-established ecosystems, commonly found in older and more stabilized sludge.

As wastewater treatment progresses, the microbial community evolves, and older sludge develops a diverse array of organisms including rotifers, which play a role in the breakdown of organic matter and help maintain ecological balance within the treatment system. Their abundance suggests that the sludge is less variable and has reached a more mature state, reflecting a higher level of stability and efficiency in the decomposition of organic materials.

In contrast, young sludge would not support a robust population of rotifers, as it is typically characterized by a less diverse microbial community and more actively growing microorganisms that have not yet stabilized. Stable sludge might imply a balanced microbial community, but the specific indicator in this case is the abundance of rotifers, which is more closely associated with old sludge. Thin sludge, on the other hand, generally refers to sludge that has a lower solids concentration and isn’t a significant indicator of mature microbial activity.