- Nematodes (worms)
- Bristle worms
- Tardigrades (among the most complex metazoa in wastewater)
Multicellular indicator organisms - rotifers, nematodes, tardigrades - Are they a good or bad in wastewater treatment systems?
As a wastewater treatment system "matures" (decrease in soluble BOD5), dissolved oxygen concentrations eventually rise to levels that can support multicellular lifeforms. Unlike bacteria (prokaryotes) and protozoa (eukaryotes) which are all single cellular organisms, metazoa are more complex organisms with differentiated cells. These organisms feed on microbial floc and protozoa present. While seen with excellent water quality, an abundance of metazoa indicates an older sludge. The biggest problem with older sludges (very low F/M) is the increase in effluent turbidity and pin floc carryover in the secondary clarifiers. Common wastewater metazoa include:
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