Nematodes in activated sludge - what do they tell us about the process?
Nematodes are metazoa that are often seen in various activated sludge configurations. They are beautiful, with a “cylinder” shape, and their length can range from 200-300 microns to even more than 1,000 - pretty big compared to other microorganisms in the basin. It’s hard to miss them due to their unique motion, as their muscles run only lengthwise. Some of them have teeth (there are a few thousand species of nematodes), and they eat bacteria, and sometimes other nematodes as well!
Their interpretation can be tricky (!). By the book, they are commonly associated with long SRT and mature biomass. However, we often see them in healthy process conditions, just as part of the microorganism community.
The key here is to know your specific plant baseline. If the abundance of nematodes rises - and they become the dominant microorganisms, or one of the most dominant - it is a sign that it may be time to consider increasing wasting to reduce the sludge age.
Now to the point that we find out most interesting about nematodes & process health:
From our experience at Maji, there is also a hidden layer in nematode behavior: keeping track of them is extremely useful for detecting rising stress conditions in the reactor (like low DO, FOG, toxicity, and more). This is something that is not mentioned a lot in the literature, but in practice, we see it more and more in both municipal and industrial plants.