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Algae, Yeast and Fungi

Typical Biological species are found that could cause corrosion and Biofouling

  • Fungi
  • Mold
  • Yeast
  • Algae
  • Aerobic and anaerobic bacteria
  • MIC bacteria (sulfate-reducing, acid producing, nitrate reducing,
  • Iron/sulfur oxidizing)
  • Slime-forming bacteria
  • Iron/manganese depositing bacteria
  • Thiobacillus spp., Gallionella spp., Sphaerotilus spp.

Yeast and Fungi

The presence of large amounts of yeast or fungi can indicate a low pH, or existence of fermentative conditions. There are more than 75,000 species of yeast and fungi, which include mold, smut, rust and mildew. They may be colorless or cover the entire color spectrum. Most grow best in warm, dark, moist places. Most are aerobic with low oxygen demand. A few, including yeast, are anaerobic. Fungi can grow on almost any surface and are considered an attributing factor to wood deterioration. Both yeast and fungi are commonly transported by air currents. They are relatively large and can easily be identified with microscopic analyses.

Image of Yeast and Fungi


Two forms of fungi commonly encountered are molds (filamentous forms) and yeast (unicellular forms). Molds can be quite troublesome, causing white rot or brown rot of the cooling tower wood, depending on whether they are cellulolytic (attack cellulose) or lignin degrading. Yeast are also cellulolytic. They can produce slime in abundant amounts and preferentially colonize wood surfaces.

Identification of Fungi
Fungi are extremely large, non-motile filaments (300-1000 µm). They can be straight, irregularly curved or bent filaments with true branching. Cells are very rectangular (3-8 x 5-15 µm) with very large trichomes and contain organelles and large intracellular granules and structures. A heavy cell wall is usually present.

Fungi and yeast are usually found in environments where there is a low pH. They are usually common in a biotower or a trickling filter. They can cause "plugging or ponding".

Control of fungi and yeast
Low pH is usually the cause of fungi and yeast. pH can be increased on the influent or in the MLSS to above pH 6 and usually with a little bit of time they disappear.

Identification of Yeast
Yeast are a group of unicellular fungi a few species of which are commonly used to leaven bread and ferment alcoholic beverages. Most yeast belong to the division Ascomycota.

Similar Organisms
Yeast can be similar to Tetrads

The presence of large amounts of yeast in the wastewater can indicate a low pH, the existence of fermentative conditions, or a severe phosphorous deficiency. Raising the pH above 7 will usually make the yeast disappear.


Algae primarily occur in the tower deck area because most species require sunlight for photosynthesis and growth. Algae slimes can plug distribution nozzles and troughs in the cooling tower deck, causing poor water distribution across the tower and hence reduce cooling efficiency. Water intake screens may also become plugged by algae slimes that can slough off from the tower. The growth of algae may provide a food source that encourages the growth of other organisms, such as bacteria and fungi.

Algae are typically photosynthetic organisms. Green and blue-green algae are very common in cooling systems. Blue-green algae are now classified with the bacteria and are called cyanobacteria.

Algae can be single celled and free floating, filamentous and cause mattes or can be slime forming.

Algae require control because the biomass can also break loose and cause exchanger fouling. When this happens, slimy, rubbery masses form, which cause plugging and decrease the tower efficiency. Various types of algae can be responsible for green growths, which block screens and distribution decks. Severe algae fouling can ultimately lead to unbalanced water flow and reduced cooling tower efficiency.