POOLPAK Technical Library

Alternative Pool Treatment:Copper Silver Ionization

CoPPer SIlver HISToryCopper and silver have been used throughout history due to their bactericidal and algaecidal qualities especially for water treatment. In ancient Greece, the silver lining of wine flasks was common to preserve freshness. Prior to antibiotics, silver was also widely used to treat infections. Silver continues to be used as a primary topical application for severe burns where prevention of bacteria buildup is important for healing.

Copper is also known for its natural bactericidal and algaecidal properties. Copper is commonly found in household plumbing. The extra bactericidal properties by using bronze doorknobs over stainless steel doorknobs in hospitals has also shown a decrease in the transmission of pathogens. Lately, copper silver ionization has taken particular prominence in the treatment of hospital water to prevent the buildup of Legionellis bacteria which is responsible for Legionnaire’s disease. This method is preferable to previous methods of thermal or superchlorinating treatments due to the residual effect of copper and silver disinfection.

Copper-Silver Ions: How are they generated?

There are two methods for copper-silver ion generation: active and passive. Active generation requires a weak voltage applied between two electrodes by a process known as electrolysis. As electrons are removed from the anode, copper (Cu+, Cu2+) and silver ions (Ag+) are released in the water. Most of these ions are carried away by the flow in the chamber before interacting with the cathode. The composition of the anode typically determines the ratio at which ions are released. The rate of release depends on the flow rate of the pool treatment system as well as the voltage applied to the electrodes. The gradual wearing away of the electrode means the electrode needs replaced typically on an annual basis.

Passive systems are those where the metal ions are already available. The ions may be time release through erosion of ceramic beads or flow release from ion-impregnated resin beds. These systems generally do not require power input. The flow-through chamber is designed to release the ions at the appropriate concentrations depending on the flow rate of the pool treatment system. These are typically plug-in cartridges that can last six months to a year before requiring replacement. Both systems are designed to produce ion concentrations in the range of 0.4-0.8ppm for copper and 5-50ppb for silver.

Since copper-silver ionization is not a standalone pool treatment, there are also additional considerations. Some systems include chlorine addition to maintain free chlorine at 0.5-1.0ppm. As ionization systems may cause staining of pool surfaces at high concentrations, sequestering agents may also be required. These chemicals are used to keep the metal ions from forming complexes with organics that may stain the pool. This process typically only happens at elevated levels of both copper ion concentrations (>0.8ppm) and chlorine concentrations higher than 1ppm.

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Copper-Silver Ions: How they work?

Copper and silver ions work together to disinfect systems. Some studies claim a synergistic effect where the combination of silver, copper, and chlorine provides greater disinfection than if each were used separately. This mechanism is poorly understood but is typically described as follows. The positively charged ions are naturally attracted to negatively charged site on the cell walls of viruses and bacteria. This attraction results in electrostatic bonds, which distort the cell membrane allowing silver ions easier access to enter the cell. These ions then attack the cell by binding to specific sites of the nucleic acids, respiratory enzymes, and proteins. This action immobilizes these components preventing growth and especially replication. It should be noted that this mechanism is much slower than that for chlorine.

For this reason, copper-silver ions are not a means of primary disinfection for swimming pools. For ion only systems, typical contact times for several pathogens are on the order of hours whereas similar levels of chlorine residual can disinfect rapidly on the order of seconds to minutes. For this reason, a minimum chlorine residual of 0.5-1ppm is required with these systems.

Also, unlike chlorine or ozone, copper and silver are not oxidants and do not react with organics from skin, sweat, or other fluids. This is positive in that the residual level of copper and silver ions remains relatively stable. However, to prevent buildup of organics, the chlorine residual is also required to burn up organics.

Recommendations

Currently, only chlorine and bromine are approved for primary disinfection of commercial swimming pools. Copper and silver ion systems appear to be more suitable for drinking water applications for closed water systems. As swimming pools are open systems where contaminants are continually being added by bathers, copper and silver ions are insufficient to treat contaminants in the time before they may infect other bathers.

As chlorine residual is still required for these systems, the copper silver ionization system also seems to introduce further chemicals and complexity to the already troubling issue of pool chemistry management. The metal ions require periodic testing to ensure the recommended levels are maintained. Elevated levels may cause staining of pool surfaces or “green hair” effects on bathers. Sequestering agents can combat these staining effects but this requires the addition of even more chemicals. Periodic cleaning of fouled electrodes and the regular replacement of cartridges or electrodes adds additional costs to pool management.

The general recommendation is that these units be used only in residential, light load conditions with residual chlorine. They may also be explored as a supplemental treatment option with ozone or UV to provide an additional residual disinfection for pool waters. The subject of whether this is a feasible application is out of the scope of this article.

References:

“Copper in Drinking Water.” Division of Health, Wisconsin Department of Natural Resources. 28 January 2003. 1 April 2011. http://www.dnr.state.wi.us/org/water/dwg/copper.htm

“Water Chemistry for Swimming Pools.” North Carolina Division of Environmental Health, Department of Environment and Natural Resources. 2011. 14 March 2011. http://www.deh.enr.state.nc.us/ehs/quality/wph.htm

Hambidge A. “Reviewing efficacy of alternative water treatment techniques.” Health Estate. 2001 Jun; 55(6): 23-5. http://www.ncbi.nlm.nih.gov/pubmed/11447890

“Pool and Spa Safety: Background Information and Frequently Asked Questions.” Australian Government, Australian Pesticides and Veterinary Medicines Authority (APVMA). 2009. 1 April 2011. http://www.apvma.gov.au/use_safely/pool/background.php#_5