One of the most challenging filament types to diagnose is Eickelboom filament type 0581. It’s a curved or coiled shaped filament located inside the flocs with 0.5-0.8 µm diameter, no visible septa (cross-walls), and Gram negative staining characteristics. Based upon personal experience as well as discussions with colleagues, type 0581 appears to be one of the least common filament types observed in activated sludge processes. Type 0581 is recognized as an organic acid filament type, however due to its rarity, there are likely other factors involved with its growth.
From a taxonomic perspective, type 0581 filament types are most generally believed to be correlated with the Chloroflexi phylum, and likely the Anaerolineae class. Chloroflexi phylum microbes are believed to be almost exclusively filamentous and there is high genetic potential diversity within these filaments. Due to the high amounts of genera with suspected similar filamentous morphology characteristics, we are currently involved in an academic study with the Georgia Institute of Technology in which one of the theories we are looking into is whether Chloroflexi genotype to phenotypes correlations may be more useful at higher taxonomic levels (such as class or family), rather than genus or species.
Chloroflexi are believed to be fairly slow growing, with many also capable of storing substrate such as glycogen under anaerobic conditions for later consumption in the aerobic zones. When type 0581 filaments are observed, we are always interested in learning as much as possible about the treatment plant process, the flow schematic and as many details about the plant as possible. A theory that has emerged about type 0581 filaments is while they are recognized as organic acid filament types, they tend to also occur in systems with higher sludge retention time values, as well as systems in which there are prolonged periods in which the RAS is unaerated. Examples of long periods in which the RAS is unaerated include high retention time in final clarifiers, large anaerobic selector zones, and plants that run contact stabilization systems but don’t aerate the initial zone of the plant.
Through microscopy, type 0581 filament types are often challenging to diagnose because they have the potential to closely resemble Microthrix characteristics, with the most significant difference being the Gram negative staining characteristic. Type 0581 filaments are the only filament in which a negative staining characteristic is important for the filament type identification. Bulking events caused by type 0581 are predominantly dependent upon the floc structure and strength of the flocs. If these (type 0581) filaments are located within strong flocs, they do not appear to cause bulking and likely serve as a strong backbone to support flocculated bacteria, whereas if the flocs are not as strong, type 0581 filaments may create open/diffuse flocs that do not settle well due to their lower mass per surface area.
Long term control of type 0581 involves reducing the concentration of volatile organic acids. While reduction of volatile acid formation is variable, potential areas of interest include reducing solids retention time in primary clarifiers, reducing potential septicity in collection systems, increasing RAS rate or internal recirculation flows (dilute organic acids), and more. In certain instances, if filamentous bacteria associated with higher SRT values are present, increased wasting is sometimes successful. Other options (depending upon individual treatment plant logistics) may include settling aids, and potentially selective RAS chlorination, which is only generally more desirable if filaments are extending from the flocs when viewed at lower power magnification under the scope.
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.
