One of the largest. Bristle worms in wastewater treatment. What do they tell us about the process?
Bristle worms are multicellular organisms, part of the group known as metazoans, which also includes rotifers, nematodes, and water bears.
Unlike bacteria and protozoa, they are larger, segmented, and reproduce sexually.
You can often recognize them easily: they have bristles along their bodies, segmented sections (red dots that can be seen in Bright field mode, like in one of the images), and in some cases, small eyes near the head. In fact, they are large enough to be seen with the naked eye, usually between 300 µm and 1 cm.
Bristle worms.
Bristle worms feed on bacteria, algae, and smaller protozoa, but they don’t contribute much to the treatment process itself. Their main value is as bioindicators.
When you start to see bristle worms, it usually means the sludge age is long and the F:M ratio is low. They develop slowly, so their presence suggests the biomass is mature and the process is well-aged.
Seeing a few bristle worms is not a problem. it usually indicates a stable, older sludge.
When does it become a RED flag? If dominant, they indicate:
The sludge is old, and food is limited.
The F:M ratio is low.
It may be time to check wasting rates and ammonia concentrations.
In summary, a few bristle worms are a normal sign of maturity. Too many, and it’s the biomass telling you the process has aged beyond its optimal point.