The ferrous iron is converted to insoluble ferric hydroxide. This leads to tuberculation attack which results in increased flow resistance and restricted carrying capacity. Fungi are most often found on the wooden structures of cooling towers such as the fill or the support members. Fungal attack of the wood usually means a permanent loss of the strength of the wood structure. Algae require sunlight to grow so they are found in the open, exposed areas of the cooling tower.
Algae grows in dense, fibrous mats that can plug the distribution trays or piping.
Algal growths also provide an ideal growth area for anaerobic bacteria. The objective of a effective microbiocide program is to expose the microbial population to a sufficient dose of biocide for a long enough time to achieve the desired effect. Biocides may be fed continuously through the use of automatic feed equipment. More often they are fed on an intermittent basis because of economic considerations or effluent restrictions. An effective biocide program will include the use of two biocides of differing types which are fed in an alternating manner.