Algae are the most common cause of slime problems in open water systems. They are simple plants which contain chlorophyll. As such, they require air, sunlight and water for their growth. Lacking any one of these elements, they will not grow. Algae normally grow more profusely on the top deck of cooling towers. They are also found whenever they can attach themselves to wet walls that are well ventilated and obtain some light. In large open reservoirs, the algae slimes often detach and are found as free floating masses. Often algae form a bed or starting point for bacterial slimes to grow.
Bacteria, the smallest members of the animal world, can adapt themselves to many unusual situations. Most bacteria require air - some do not. No bacteria require light. They are found everywhere where even a trace of organic matter is available. Bacterial slimes are most common in paper making operations and are often found in conjunction with algae in cooling water systems.
The principal threat posed by algae is plugging of tubes, screens and pipe lines and loss of heat transfer efficiency. The bacteria which thrive along with the algae cause corrosion. The bacteria live under the algal masses, particularly around the point of attachment to metal and wood parts. Here the sulfate reducing strains create low pH regions and iron reducing strains produce slimy iron hydroxide floc. Chemical sludge at the bottom of a setting basin may often contain bacterial slimes. These growths cement the sludge particles into large hard-to-handle clumps.
Fungi often are larger plants commonly recognized as molds and mildew. They require moisture, atmospheric oxygen and a point of attachment. Because of this, fungi are usually found above the water line or associated with bacterial surface slime. Several particular types of fungi require cellulose as a source of carbon in their growth cycle. These fungi cause surface rot and internal decay of wooden cooling towers. The plenum chamber or de-mister sections of a cooling tower is the most common place for fungi to grow. Towers treated with high concentration of oxidizing agents are particularly susceptible to this type of attack. This is due to delignification of the wood by the oxidizing salts and the resulting ease with which the water can then leach out the preservatives. Once the unpreserved wood is exposed, decay can spread rapidly unless treatment to inhibit fungi is used.
Algae Description
Chlorococcum macrostigmatum – GREEN ALGAE – may be aquatic or found on moist surfaces, generally in relatively dirty water; relatively resistant to copper sulfate.
Chlorella vulgaris – GREEN ALGAE – unicellular planktonic form causing a green turbidity throughout contaminated water, relatively resistant to copper sulfate – may cause filter clogging.
Scenedesmus basilensis – GREEN ALGAE – generally surface water algae which may impart taste and odor to the water – causes a general green turbidity – very resistant to copper sulfate.
Plectonema boryanum – BLUE GREEN ALGAE – found in aquatic habitats.
Anacystis – BLUE GREEN ALGAE – cells grow in a slimy matrix which may appear yellow or brown with age – may cause taste and odor problems.
Sphoerocstis – GREEN surface ALGAE – whole cells grow in a slimy matrix.
Mesotoenium – GREEN ALGAE – cells embedded in a gelatinous matrix adhering to walls, rocks, etc., or may be free-floating masses.
Gamphosphoeria – BLUE GREEN ALGAE – may cause odor in water – several cells embedded in a gelatinous matrix – usually a surface form.
Oscillatoria – DARK BLUE GREEN ALGAE – commonly referred to as a black algae – may cause taste and odors in water – commonly found attached to surface of cooling towers, etc.
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