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.

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.

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".

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.

More on Yeast and Fungi

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 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.

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

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 branched or straight

Algae can be curled or in small free floating clusters with a slime coating

Anabaena                                                             Woronichinia naegeliana

Blue Green algae or cyanobacteria and Beggiatoa              Achnantes taeniata is a brown algae Filamentous

Aphanizomenon flos-aquae Scenedesmus and Flagellate

Branched algae                                              Algae slime on cement and metal

Diatoms are algae enclosed by a silicaceous cell wall and may also be present in cooling towers but generally do not play a significant role in cooling system problems.

1/5 of all corrosion is typically caused by microorganisms and biofouling

The most common MICs can be categorized into sulfate reducing bacteria (SRB), iron oxidizing bacteria and acid producing bacteria (APB).

Thiobacillus, Sphaerotilus natans

SRBs are characterized by hydrogen sulfide odor and blackened water or black colored deposits. Iron oxidizing bacteria generally form in filamentous clumps and can be detected under microscope by their distinct appearance due the excreted products that grow. This corrosion by iron bacteria often forms tubercles.

DesulfoVibrio                                                             Spirillum- motile spiral bacteria

Purple sulfur bacteria                                                             Spirillum with sulfur granules

DesulfoVibrio

Sphaerotilus natans or S. natans

More on Filamentous Bacteria

S Natans

Other bacteria that may be present in cooling water include Pseudomonas, Klebsiella, Eneterobacter, Acinetobacter, Bacillus, Aeromonas, and Legionella

Spore forming bacteria

Denitrifying bacteria, or pseudomonas, can cause the loss of nitrite inhibitor in closed-water systems.

Usually plate counts with differential media are used to determine the exact count of these types of bacteria

If you are interested in having a Cooling Tower Microscopic analyses of your system performed

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