Fungi at low levels are common or insignificant and often incidental visitors to wastewater treatment processes, although at higher abundance fungi may indicate low pH values somewhere within the system. Fungi may rarely cause or contribute to bulking events. More commonly, low pH itself may cause weak floc structure, high dispersed growth and disruption of cellular enzyme activity, which may lead to undesirable treatment performance.
Fungi are recognized as a filamentous, however, rather than being bacteria, they are represented by their own kingdom (the fungal kingdom) which also includes yeast, mold and mushrooms. Fungi contain chitin (a polysaccharide) within their cell walls, which may contribute a viscous property to samples in which high fungi are present. We have witnessed high fungi present in occasional biological slimes (likely due to the polysaccharide), and there is high suspicion that high fungi and yeast may be a potential membrane foulant for membrane bioreactors, also likely due to polysaccharide.
Fungi are recognized heterotrophs that utilize organic carbon for substrate. The cells of most fungi contain hyphae (filament structures) at the tips which are the mechanism for growth. Mycology is a branch of science dedicated to the study of fungi. The fungal kingdom is immensely diverse, however, the true biodiversity of the kingdom is relatively unknown at this time. Fungi are recognized by their morphological characteristics which include a wide cell diameter (commonly 4-5 µm) and true branching characteristics. Fungi are generally much larger than filamentous bacteria viewed under the microscope and may often be recognized at low magnifications.
Fungi and yeast sometimes enter wastewater treatment processes as byproducts from industrial processes like bakeries, or dairies, or may grow in areas of low pH (beginning at less than 7). If fungi are present in a wastewater mixed liquor sample at significant abundance, investigation of low pH within the system is warranted. Should low pH not be suspected, microbial monitoring of the influent and other side-streams (sludge handling etc.) would be recommended to determine the source of entry.
[Editor's note: Author Ryan Hennessy just released his book "Wastewater Microbiology: Filamentous Bacteria Morphotype Identification Techniques, and Process Control Troubleshooting Strategies." The book is now available on Amazon.]
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.
