Eickelboom filament type 1863 is most commonly observed dispersed in solution or occasionally near the edges of the floc at 1000x oil-immersion microscopy. The cell shape resembles small sausage-like rods typically 0.8-1.0 µm in width, 1-1.5 µm in dimension, and generally not exceeding 75 µm in length. Septa (cross-walls) are visible, and no sheath is present. Literature by Dr. David Jenkins, Dr. Michael Richard, and others associate type 1863 filament morphology with fat, oil and grease.

At a genetic level and based on our ongoing project of comparing as many micro to DNA samples as possible, filament type 1863 is most often correlated with the Acinetobacter genus. Currently, the MiDAS database recognizes 90 species of Acinetobacter, which may exist in various forms (some filamentous, and others as rods or cocci). Most often, Acinetobacter is recognized to enter wastewater treatment processes through the influent (Nierychlo, M., 2022).

Acinetobacter are aerobic heterotrophs that were once believed to play a significant role in enhanced biological phosphorous removal, although more recent findings have discredited these theories. While Acinetobacter stores higher amounts of phosphorous than most bacteria in wastewater treatment processes (similarly to Micorthrix), it has not been proven to store substrate under anaerobic conditions nor to produce orthophosphate release in anaerobic conditions at levels of polyphosphate accumulating organisms.

Filament type 1863 is recognized to cause/contribute to foaming events in wastewater due to its hydrophobic cell surface. From practical experience evaluating thousands of mixed liquor samples, type 1863 filaments are generally not the predominant filamentous bacteria in activated sludge foams, but often accompany Actinomycetes-Mycolata or Microthrix filament types. In experience, type 1863 foaming appears to be more prevalent in areas such as equalization basins and Kaldness tanks.

Earlier literature suggests that type 1863 filaments occur in low SRT systems, however experience has shown that it appears more practical to correlate type 1863 filaments with recent fat, oil and grease, as these filaments most commonly (but not always) enter wastewater treatment plants through the influent. Bulking from type 1863 filaments is rarely encountered, however if significant abundance of type 1863 is observed, recent fat, oil and grease are suspected.

Due to the variable morphological nature of the the Acinetobacter genus, the presence of Acinetobacter in DNA testing (such as 16SrRNA sequencing) may help support type 1863 filaments observed through microscopy. However, it is common to see Acinetobacter present while type 1863 filament morphology is absent under the microscope.

---

About the author: Ryan Hennessy is the principal scientist at Ryan Hennessy Wastewater Microbiology. He was trained and mentored by Dr. Michael Richard for over 10 years in wastewater microbiology, and serves as a microbiology services consultant. Hennessy is a licensed wastewater treatment and municipal waterworks operator in the state of Wisconsin and fills in as needed for operations at several facilities. He can be reached at ryan@rhwastewatermicrobiology.com.