In recent literature Eickelboom filament type 0675 and type 0041 have been combined as a single filamentous bacteria morphoptype. Note that the descriptions of these filaments are nearly identical with the only significant difference being a larger diameter for filament type 0041.

From a combined standpoint, morphotype 0675/0041 may possess a diameter ranging from 1µm to 2.2 µm with a square-like cell shape. These filament types are often located within the floc structure and usually (but not always) contain attached growth. The recognized growth cause for type 0675/0041 filaments is high sludge retention time (SRT). In many instances low food to microorganism (F/M) ratio on the back end of the biological treatment process appears to be another contributing factor.

From a genetic standpoint, there appears to be high diversity within the 0675/0041 morphotype, including members from the Chloroflexi and Saccharibacteria phylum. It is believed that the Saccharibacteria phylum (formerly TM7) members degrade exocellular polysaccharide as substrate, allowing them to compete well when there is low amounts of external carbon available, and these filaments are likely more closely attributed to low F/M values.

Chloroflexi phylum members tend to occur at higher SRT values with many filament types capable of storage of sugars and other carbon sources under anaerobic conditions. Based on literature such as the MiDAS field guide, Sevior labs, and early indications from a study we are currently working on with Aster Bio, the following genus and Aster Bio taxonomy identification numbers are candidates for the ability to possess type 0675/0041 morphology:

• Ca Saccharimonas (Confirmed by Sevior/suspected by Ryan Hennessy)
• Herpetosiphon (Midas field guide confirms genus may be filamentous/Hennessy suspects potential correlation to 0675/0041 filament morphotype).
• Aster Bio taxonomy identification number candidates, according to Hennessy:1508635; 1382929; 1382930; 494964; 475964; 1332188; 200795; and 292628. These numbers can be further referenced here.
• Note: Other genus associated with type 0675/0041 morphotype may be found here. These have not reflected my personal findings from plants in the United States and Canada as of this time, however, they have been confirmed in Europe.
• Additional Reference may be found in the MiDAS Field Guide.

Control strategies for bulking events associated with filament type 0675/0041 include increasing the waste activated sludge rate or decreasing the SRT value; increasing the F/M ratio (if possible); short-term use of coagulants and settling aids; and in certain instances, RAS chlorination to selectively eliminate filaments should they be extending from the floc structure.

Please note that each individual circumstance is specific and professional microscopic evaluation followed by a discussion of plant logistics, urgency, etc. is recommended prior to any official recommendations.

---

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.