Use of GeoSIL in Municipal Water Authorities    

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 (Biofilm) 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

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, 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 for the treatment of potable water by the Drinking Water Inspectorate in the UK.  

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  are 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 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.

Sewage Treatment with GeoSIL  

Oxidation of Sulphides in Raw Sewage

Nuisance odours associated with sewage reticulation systems and associated treatment plants, have always been an area of concern for municipal authorities. 

Sewage odours are of course, not a new problem and many control techniques have been evaluated or utilised to date.

Several odour control systems have been utilised which treat foul odours once evolved in the gaseous phase, however, this is treating the symptom rather than attacking the problem at the source, being the raw sewage. It is worth noting that in many cases treating the odour producing gases, once removed from raw sewage, is the only economically viable option, however, in most applications the prevention of sulphide formation in the raw sewage is necessary.

Sulphide is produced in sewage systems as a result of decomposition of organic matter but is primarily the result of bacterial reduction of sulphate. Hydrogen sulphide (H2S) escaping into the air from sulphide containing wastewater is the primary cause of nuisance odours. The threshold odour concentration of H2S is between 0.025 and 0.25 ppb. H2S is very toxic and becomes undetectable after exposure to high concentrations. It is therefore claimed the lives of numerous workers in sewage systems. It attacks metals directly, and indirectly, and causes serious corrosions to concrete sewers because it is oxidised biologically to sulphuric acid on the pipe walls. Where sewage is retained in the reticulation system, for sufficient time to deplete all dissolved oxygen, the resultant anaerobic conditions promote the growth of sulphate reducing bacteria, which in turn oxidises sulphate to sulphide.

Several treatments have been utilised for the control of sulphides in sewage systems, however, most are either cost prohibitive or only partially effective. GeoSIL  is selective in many reactions, such as its inability to react with ammonia compounds, which enables it to be utilised for direct injection into sewage.

The common perception that the treatment of nuisance odours in the gaseous phase is the most economical approach is ill founded because with that approach no consideration is given to the expense of system corrosion and removal of sulphides in the raw sewage.

GeoSIL has been extensively used for sulphide control in sewage. It is used in various forms world-wide as the oxidant of choice due to the ease of application and its environmental acceptability, plus:

q       GeoSIL is simple to dose

q       The reduction of GeoSIL adds oxygen to the sewage.

q       GeoSIL is very effective for oxidising sulphides.

q       There are NO detrimental or hazardous by-products.

Disinfection of Secondary and Tertiary Sewage.

The discharge of treated sewage to the environment, has recently become a topical subject both here in the UK as well as the world over, due to pollution of our beaches, rivers and general waterways. Although not all primary, secondary and tertiary treated sewage is disinfected prior to discharge to the environment, this situation will surely change in the near future.

Chlorine has long been favoured as a disinfectant for both water and wastewater treatment, due to its bacterial effectiveness, initial low cost, convenience, and relative long lived residual. However, chlorination, as normally practised in wastewater treatment, results in the formation of trihalomethanes and other chlorinated organics that are undesirable from a water pollution point of view. A further undesirable effect is the corrosion damage chlorine causes on the treatment equipment and plant.

An alternative treatment to chlorine should be cost effective, provide a measurable residual, be easy and safe to handle, and produce little or no undesirable by products.

GeoSIL is the obvious choice for an alternative oxidant to chlorine, as it provides several desirable characteristics, which includes:

q       Is a strong oxidant which is effective over a broad pH range

q       Provides an easily measurable residual.

q       Does not react with ammonia.

q       Does not react with organic matter to form toxic by-products

q       Does not require long contact times

  Considerable interest has therefore developed in the use of GeoSIL as an alternative for disinfection of wastewater. GeoSIL is most applicable where secondary or tertiary treated sewage is to be discharged into receiving waterways, whereby chlorinated organic by-products will have a deleterious affect on the ecosystem. Concern is also raised where chloro-organic by-products may find their way into public water supplies, which could result in adverse health effects to humans.

GeoSIL Advantages

q       GeoSIL can be dosed via a simple dosing tank and pump

q       GeoSIL breaks down to oxygen and water leaving no toxic by-products

q       GeoSIL oxygenates wastewater decreasing BOD and regrowth of anaerobes

q       GeoSIL is UV stable allowing for safe relative long lasting residual, and preventing regrowth

q       GeoSIL is effective against all microbiological growth including, spores, viruses

Potable Water Treatment with GeoSIL

Significant attention has been given over the last few years to the disinfection of drinking water. New analytical techniques and a broader understanding of aqueous chemistry has highlighted a significant problem in the use of  traditional disinfection techniques, namely the formation of trihalomethanes (THM's), which have now been shown to be hazardous to human health. Of the viable disinfectant alternatives GeoSIL , none offer as complete an answer to the many problems encountered in treatment of drinking water.

GeoSIL is an oxidant which behaves as a powerful disinfectant in drinking water and acts without causing tastes and odours or harmful by-products . It is effective in both clear, turbid, or coloured water and has a rapid rate of reaction. Contact times are relatively short, requiring only 25 to 35 minutes for disinfection.

Furthermore, GeoSIL can be employed as a sole disinfectant.

Other disinfectants such as UV or ozone are limited in their application by their high capital outlay. UV can only be effective where the water is of sufficient clarity and depth to achieve light penetration and therefore disinfection. Also, no form of residual is achieved with either Ozone or UV to maintain microbiological control. These mechanical systems generally have high associated running costs. For existing UV or ozone systems it will be used to provide a reliable and safe residual.

The other alternative, Chlorine Dioxide, has also limitations with capital installation costs and fairly expensive running costs, and also presents significant hazards in terms of handling.

Chlorine's effectiveness is limited as a microbiocide since it is pH dependant. It dissociates to form hypochlorite ions as the water pH increases.  

GeoSIL is a ideal oxidant for potable water disinfection particularly as it is effective as a broad spectrum microbiocide and virucide in all types of water conditions without creating taste, odour or harmful by-products.

GeoSIL provides significant technical benefits over alternative treatments such as chlorine. With many applications, GeoSIL is the most economical treatment option given a set of performance criteria. It is also important to note  that GeoSIL will often perform tasks that other treatments will not do at any price.