Nematodes are a metazoan commonly found in wastewater treatment processes in small numbers. It is believed that nematodes typically enter wastewater treatment processes through attachment to soil associated with inflow and infiltration.

Most nematodes found in wastewater treatment plants are typically 2-3 microns in length and prey on floc particles and bacteria, such as fecal bacteria. Nematodes are aerobic organisms and their growth is inhibited in anoxic and anaerobic environments. While nematodes tend to be found more frequently in systems with higher sludge retention times, we don’t recommend trying to correlate them to sludge age, food-to-microorganism ratio, or use their presence or absence as the basis for any operational control adjustments.

We have analyzed mixed liquor samples with sludge ages of under three days in which nematodes are present. Also we have observed high amounts of nematodes briefly in mixed liquor systems shortly after final clarifiers are taken offline and cleaned out and suspect they may inhabit the sludge blankets or grow on the walls of the clarifiers.

Diversity is very high and there are over 20 different orders recognized in the phylum Nematoda. There is some debate in the scientific community among the actual number of species of Nematodes, with lower estimates around 25,000 species and higher estimates up to over a million species with over 2,000 genera.

In nature, nematodes have successfully adapted to nearly every environment including saltwater, freshwater, tropics, and the highest and lowest of elevations. Wikipedia theorizes that there are approximately 60 billion nematodes inhabiting the topsoil of the Earth per each human being present.

Nematodes in nature can reach up to 2-3 inches in length with some parasite species reaching lengths of up to 3 feet. There are about 35 species of nematodes that can live inside of humans.

Nematodes have many unique characteristics, such as having no stomach muscles, as food is moved through the digestive system as a result of body movements. Other nematodes have teeth and stylets which can be thrust into their prey. Reproduction varies with sexual reproduction or self-fertilization of eggs by hemaphrodite species.

From a practical standpoint in wastewater, seeing nematodes under the microscope is worth noting. Though their presence is common and nothing that would typically warrant additional concern, they are beneficial in many instances (trickling filters, etc.).