Industrial and Commercial Chemical Engineering Services - Houseman Watermarc

ALGAE, SLIME & BACTERIA

Algae

Algae are a form of microscopic plant life and most species are a shade of green. A typical example is that which is seen floating on ponds. Because sunlight is necessary for the growth of most algae they are often found at the head of a cooling tower, where the higher temperature also favours growth.

Algae can grow quite rapidly forming a thick mat or organic material which can clog water distribution nozzles reducing the cooling capacity of the system. Occasionally, dead algae can break away into the recirculating water and cause narrow waterways to clog or indeed settle in condenser tubes reducing heat transfer.

Slimes (Biofilms)

Slimes are usually grey or yellow in colour and are accumulations of mucoid material produced by bacteria during their growth. They may also appear red or black as a result of entrapped dirt or iron corrosion products. Slimes tend to cling to system surfaces and act as a binder for suspended particulates. This will cause interference with the flow of water through tower nozzles and low flow passages, resulting in high head pressures in refrigerant condensers. They will cause odours and greatly increase localized corrosion wherever they accumulate.

A biofilm such as pseudomonas is the development of bacteria colonies on a surface which is protected by bacteria-produced membrane. When unchecked and provided the organisms obtain sufficient nutrients a biofilm can quickly multiply, particularly in areas of low water flow.
Given the right conditions, certain bacterial slime forming organisms can divide and multiply within 20 minutes.

Biolfilms which are attached to surfaces are referred to as sessile. Bacteria organisms free floating in water are termed planktonic bacteria.
The difference between sessile and planktonic bacteria is significant in that, the relative ease of accurate monitoring and control of planktonic bacteria does not necessarily apply to sessile bacteria.

Biofilms (sessile) once established cannot be accurately monitored and the skin (slime) is resistant to many biocides and can be resistant to normal flushing procedures.Biofilms are implicated in a wide range of water processes, both domestic and industrial. Biofilms grow on the surface of process equipment and impede the performance of the equipment, such as degradation of heat transfer or plugging of filters and membranes.

Biofilms growing on cooling tower fill can add enough weight to cause collapse of the fill. Biofilms cause corrosion of even highly specialized stainless steels. Biofilms in a water process can degrade the value of a final product such as biofilm contamination in a paper process or the attachment of even a single cell on a silicon chip.

Biofilms growing in drinking water distribution systems can harbor potential pathogenic organisms, corrosive organisms or bacteria that degrade the potable water quality as well as aesthetic quality of the water.