food grade product line by Water Services Ltd

Fungi are simple organisms containing no chlorophyll. They can be unicellular or filamentous. They usually require less moisture and can survive at lower pH levels than algae or bacteria. Fungi can reproduce both sexually or asexually (sporulation). Two commonly known classifications of fungi are yeasts and molds. The yeast type of fungi do not cause wood rot, but instead can proliferate to high numbers and foul heat exchangers surfaces. The most serious damage caused by molds is destruction of cooling tower wood. Fungi obtain their food from plant and animal matter by secreting enzymes into their surrounding. Cellulytic fungi use cellulose as a source of carbon, and in dong so, they destroy the wood. The most generally accepted classifications of fungi wood destruction are soft rot (sometimes called surface rot), brown rot and white rot (sometimes called pocked rot or deep rot).

Soft rot occurs primarily on wood surfaces which are heavily wetted, such as the tower fill. The cellulose (the material giving the rigidity to wood) is destroyed, which the lignin (the cell cementing material in wood) is not significantly attached. Wood which has suffered soft rot, upon drying, will reveal cracks perpendicular to the grain, giving a cross-checked appearance to the wood. Also, the wood becomes very brittle; if broken across the grain, the wood will not splinter, but will break evenly in a straight line along the edge.

Brown rot is similar to soft rot, but it occurs inside the wood. Again, the cellulose is metabolized, leaving the lignin little affected. A brown color occurs as a result of the lignin residue remaining. Brown rot occurs in wood that is not fully saturated with water, allowing diffusion of air into the wood. Areas of the towers, such as the plenum, that are only contacted with water mist, are more likely to incur brown rot. Wood may suffer brown rot and lose most of its structural strength, yet it may appear, externally, to be sound.

White rot also occurs inside wood not completely saturated with water. While rot organisms digest both the cellulose and the lignin, leaving hollow pockets in the wood. Wood which has suffered white rot may also appear sound when viewed externally.