Silver News

By Jeffrey R. Ellis, Technical Consultant to the Silver Institute

The amount of silver used to purify water for drinking, bathing and recreation is expected to increase throughout the decade.

Although some applications show signs of maturing – such as pool and spa water purification systems, as indicated by industry consolidation and some failed companies – all suppliers contacted expect sales growth as world economies expand.

Along with established and growing markets for water purification such as drinking water and pools, relatively new uses of silver-based biocides for water treatment are expected. One is the growth in the use of silver biocides in commercial ice-making machinery. It is estimated that 150,000 to 200,000 such units are being sold yearly worldwide. Even more use of silver-based biocides is likely to be in refrigerators, freezers and other food storage units.

Another new development is the expectation that silverbased biocides will be used for the purification and recycling of lightly-polluted or “grey” water. Testing is under way in both the United States and in Europe. Additional sales will accrue from the use of biocidal silver coatings on cooling towers of commercial and industrial buildings for the control of legionella and other pathogenic organisms

Following is a summary of current and future uses for silver in water purification.

Drinking Water

For large and small water storage and delivery systems, chlorine and hypochlorite solutions are effective and low cost, and silver must compete with these chemicals and other technologies. The main advantages of silver-based systems are that they have no odor, are long lasting and do not create byproducts.

The important drinking water niche markets for biocidal silver are 1) purifying outdoor untreated water sources and 2) purifying potable water systems for homes and offices. For outdoor water sources, silver deposited on ceramics is used by the military and by people traveling in wilderness areas. The competing technology for this particular niche is iodine tablets. For systems designed for use in recreational vehicles and watercraft, silver must compete against both UV-light and ozone generators. In water purification systems for the home and office, filters made from silver on carbon or silver on ceramic substrates are offered by a number of companies.

Swimming Pools and Spas

For spa and pool treatment, silver peroxide and silver/copper chemical systems have been developed. These compete with chemicals including chlorine, hypochlorites and bromates. Chlorine dioxide generators and ozone generators also compete.

Silver peroxides are supplied as a liquid mixture, and treatments ordinarily last for thirty days. Cartridges or chambers containing silver and copper electrodes are also offered for water treatment in pools and spas, and these products last for a few months.

Silver/Copper systems in which silver and copper are coated on ceramic grade alumina are also on the market. Silver controls bacteria growth and copper is used to control algae. These systems are largely designed for personal pools and spas and are not effective for large installations such as municipal swimming pools. For pools, water is passed through a filter chamber containing silver and copper beads, and one filter cartridge is effective for six months. For spas, the effective time of ion release is four months.

Grey Water Recycling

One market that may hold promise for silver-based biocides is the recycling of lightly polluted or grey water. This would be useful for industrial and commercial water recycling systems that would mostly recycle shower and bath water in hotels, hospitals, nursing homes and other institutional facilities. Irrigation water could also be economically recycled. Municipal water systems, including those in New York City and several in Belgium, are researching this technology.

Ice Making

In the last two years, silver-based biocides have been incorporated into components of ice-making machinery. Among manufacturers that offer such products are Scotsman Ice Systems, Manitowoc Ice, Inc. and Ice-O-Matic. It is estimated that 150,000 to 200,000 units worldwide containing biocidal silver are now being sold. Previous attempts to use silver in ice makers have suffered because of the cost of receiving approvals from organizations that monitor and set standards for performance and health risks. Now that specific additives have been approved, it is likely that other companies offering ice and water purification machinery using biocidal silver will have a much easier time in introducing new products. Most ice-making machinery is designed for commercial and institutional use, such as in restaurants, hotels and hospitals. Traditionally, the main structural component of icemakers has been stainless steel, but molded plastic parts containing biocidal silver are now being used for components such as evaporators, water troughs and splash shields. Silver-based biocides, whether applied onto a coating or incorporated into a molded or extruded plastic, are very effective at preventing the build-up of slime and bacteria. An obvious extension of the use of silver-based biocides would be in ice-making components and other areas of refrigerators, freezers and other food storage appliances.

Food Processing

Makers of silver-based water treatment systems have also targeted food processing applications. An attempt to interest meat and poultry processors has not resulted yet in major sales, but seafood processors are beginning to look at systems with silver/copper electrodes in a chamber. One company, TP Technology (High Wycombe, U.K.), claims success in the use of a silver/copper electrode system to purify water in the processing of fruits and vegetables, and officials say that substantial sales are being made in the United Kingdom and Australia.

Commercial Plumbing Systems

Other major markets target the control of pathogens, especially legionella bacteria, in cooling towers of air conditioning units. Significant sales are already being made to hospitals and nursing homes in addition to industrial and commercial buildings. Preventing biofilm formation and cleaning biofilms at installations of industrial clients is also a niche market for silver based biocides.

Home Plumbing Systems

There has been some concern that harmful bacteria and slime could build up in plumbing systems, especially on shower head filters where crevices, heat, and a moist environment could lead to pathogenic bacterial build-up. However, it is not currently a public health issue even though it has received some attention from the National Sanitation Foundation (Ann Arbor, MI). Silver/copper and silver/carbon systems compete with other chemistries for this particular market niche.

Bottled Water

There are no claims yet of any silver-based biocide use in the production and preparation of bottled water. However, now that silver is approved for use in ice making, bottled water processing machinery may also soon follow.

Silver News - First Quarter 2005