Filament type 0411 is commonly correlated with sludge bulking events in wastewater treatment processes all over the world. 

The most distinguishing characteristics of this filament are the “hotdog-link” cell structure. The type 0411 morphotype description includes diameter ranges of 0.8-1.2 µm with sausage/rod-shaped cells ranging from 2.0-5.0 µm in individual cell length. Septa (cross-walls) are viewed in which a distinct break between each cell is observed within the filament. Type 0411 filament types are most often correlated to low molecular weight organic acid substrate. Organic acids may be naturally occurring in many industrial wastewater treatment processes, or may be formed in areas of septicity/fermentation (i.e. collection systems, lift stations and primary clarifiers)

From a genetic level, type 0411 filament morphology is most frequently correlated to the Runella genus, which contains variable filament morphology and 31 recognized species (per the MiDAS database). Based on comparing hundreds of wastewater microscopy samples to DNA analysis, it is also suspected that type 0411 morphotypes may exist in other genera within the Bacteriodes phylum, as well as possibly unclassified Proteobacteria. Various species within the Runella genus may have different metabolic functions ranging from strict aerobes to other species that are capable of fermenting sugars under anaerobic conditions.

From a practical standpoint, in wastewater treatment processes, type 0411 filament types are most commonly observed in processes that have high F/M bacterial growth rates in the initial contact zone (first 15-30 minutes) of the aeration basin. Type 0411 filaments are often found in conjunction with zoogloea bacteria morphotypes based on practical experience. While unproven, it is suspected based on experience that type 0411 filament types may also occur in highly proteinaceous wastewater that becomes septic.

Selective RAS chlorination in conjunction with increasing the SRT value are commonly practiced, however, operational control strategies for filaments are highly variable depending on circumstances, including severity of the problem, availability of settling aids for temporary issues, cost and logistics, as well as available methods for operational control based on the treatment process schematics.

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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. Hennessy's new book "Wastewater Microbiology: Filamentous Bacteria Morphotype Identification Techniques, and Process Control Troubleshooting Strategies" is now available on Amazon.