Control of Microbiological  Fouling of Water Mains 

Microbiological fouling of drinking water reticulation systems is a major problem throughout the world. Bacterial deposits in pipelines cause many problems for water supply authorities, resulting in unacceptable drinking water quality and also direct and indirect operating costs of the water treatment system.

Bacterial growth in the distribution system causes several problems, which include;

q       Intermittent dirty water to consumers.

q       Corrosion of pipelines and fittings.

q       Intermittent loss of disinfection.

q       Loss of oxidant residual.

Microbiological deposits are often associated with the deposition of inorganic matter in low velocity areas of the distribution system, such as reservoirs. Ingress of mud may occur where reservoirs are not covered, or where filtration systems are not used in the treatment plant. Where mud or inorganic material deposition occurs, bacterial growth is often present. In situations where biological deposits and/or mud deposits are present together with water containing a positive dissolved oxygen content, corrosion of pipework and metal fittings is inevitable. Specific bacterial organisms such as hyphomicrobium and pseudomonas are present in most natural water supplies and are able to grow on pipework surfaces in the presence of very low nutrient levels and high water velocities. Intermittent dirty water is considered to be a result of sudden release or sloughing off of both organic and associated inorganic deposits that have accumulated in the reticulation pipelines. These types of bacterial organisms have been shown to grow in the higher velocity areas of potable water pipelines, and in fact grow faster as the water velocity and temperature increases.

These types of bacteria are able to utilise metal ions such as iron and manganese as either a nutrient or energy source. The presence of these metals therefore significantly enhances the growth of bacterial deposits in pipelines and result in associated dirty water, or contamination problems.

Although most treated water supplies are currently adequately disinfected with chlorine or chloramine, the allowable disinfectant residual are not sufficient to prevent some bacterial growth in pipelines. Bacteria that utilise metal ions as a nutrient or energy source, largely protect themselves with a sheathing of metal oxidation products. Oxidants such as chlorine or chloramines have poor penetrating abilities and therefore do little to prevent these bacterial growths.

GeoSIL has a unique ability to penetrate and break up biological deposits, even at residual concentrations as low as the levels normally maintained in potable water distribution systems. With this biological penetration ability, GeoSIL has been shown to be the disinfectant of choice for water supplies known to have a fouled reticulation system, or where iron and manganese cannot be virtually eliminated at the treatment plant. Biological contamination of drinking water reticulation is inevitable when traditional disinfectants are utilised, however, the severity of the problem depends on several factors, such as the quality of water disinfection, oxidant residual maintenance and water contaminants such as iron and manganese.

GeoSIL has been shown to provide a water quality that is not obtainable with any other residual disinfection system, especially where biological fouling of the distribution system is evident. 

Water Mains Treatment Comparison

There are very few disinfectants that are acceptable for residual maintenance within potable water distribution systems. The most widely used oxidants currently are; free chlorine, chloramines, and Chlorine Dioxide.

Free chlorine is an effective disinfectant, however, at the residual levels tolerated by consumers in drinking water, it is often ineffective for the control of established microbiological fouling in water mains. Chlorine would be more effective if the free chlorine residual could be increased to greater than 1 mg/L, however, this would give rise to unacceptable taste and odours in the finished water.

Chloramine is a very poor disinfectant, however, it has shown to provide adequate quality water and control of biological fouling under ideal conditions in a clean distribution system. Where the distribution pipework has already been contaminated with bacterial growth, chloramination has not proven to be effective for control of microbiological fouling, and is associated problems. Chloramine will in fact, promote the growth of a nitrifying bacteria and compound problems of microbiological fouling.

Chlorine Dioxide and/or chlorine plus Chlorine Dioxide is very effective in both controlling and slowly removing existing microbiological growths in potable water distribution systems. However recent modifications to chlorine dioxide dosage restrictions down to 0.4 mg/l will render it incapable of disinfection let alone cleaning of biofouling.

GeoSIL however is used throughout Europe as a disinfectant and cleaner of choice in reticulation and mains cleaning. This treatment approach is by far, the most cost effective method of controlling this particular problem associated with drinking water particularly when the associated cost of disposal of the cleaning solution is considered and when the side benefits of the provision of taste and odour free, disinfected water are considered.

For the control of biological deposits in potable water distribution systems, GeoSIL should be considered due to its ability to remove biofouling through oxidation of the matrix and its obvious suitability to disinfection of potable water without tastes, odours or toxic by-products.

GeoSIL is approved by Secretary of State for the Environment under Regulation 25(1)(a).  

GeoSIL is unaffected by photo-decomposition, aeration and is temperature stable to 99'C, therefore, uncovered or poorly designed reservoirs where turbulence is caused, will not deplete the reserve residuals of disinfectant.

For the treatment of drinking water, the primary by-products from the reduction of  GeoSIL is oxygen and water making it particularly suitable for potable water disinfection. This makes GeoSIL an excellent alternative to traditional disinfectants. 

Where there are existing UV or ozone disinfectant systems GeoSIL is regarded as being complementary to the total disinfection process as a residual disinfectant and biofouling reduction agent.

The advantages of GeoSIL over traditional approaches include:

Bacterial growths in the pipework and reservoirs are prevented while existing deposits are gradually removed, decreasing the demand on residual disinfectant.