Technical How-to - swimming pool non chlorine treatment purification specialist

- THE AQUABRITE SYSTEM -

Introduction

The Aquabrite system is based upon the principle of "oligodynamics". The term "oligodynamic" is used to differentiate between ordinary poisoning death by metallic salts on living organisms at high concentrations and antibacterial activity of metal ions at much greater dilutions. "Oligodynamics" was first used by a researcher, Von Nageli (1893) when he formed it from two Greek words "oligos" meaning small and "dynamis" meaning power (Lawrence and Block, 1966).

There have been numerous studies of oligodynamics dating from about 1890 to the present time. The general conclusion is that there is a form of silver ion which is antimicrobial, stable and non-toxic to man (Lawrence and Block, 1966). Silver may be added to water as a sparingly soluble salt, colloidal metallic dispersions or generated electrolytically. The water may also be passed through media coated with metals.

The Aquabrite System utilises electrolytic copper and silver.

In practice, copper and silver metals are made into an alloy from which electrodes are cast. When the electrodes are placed in the pool filtration system and a small current of electricity is allowed to flow between the two electrodes, copper and silver ions are released into the water from the positive electrode (anode). The ions are swept into the pool by the rapid flow of water and become part of the pool water chemistry. These metal ions are completely safe to use and provide a residual disinfectant and algicidal activity throughout the pool to prevent bacterial slime on pool surfaces and inhibit the growth of algae.

Copper

The World Health Organisation has imposed a limit for soluble copper in drinking water of 2.0 mg/L. The limit is set at that concentration because a metallic taste may be imparted to some waters. Copper ions serve as an effective algicide and its concentration can be measured with a simple test kit and therefore controlled. The Aquabrite system operates within the range of 0.2-1.0 mg/L. "There is no scientific data available to support the toxicity of copper in drinking water" (Dresher, 1995).

Silver

The world Health Organisation limit for silver in drinking water has been set at 0.05 mg/L. Excessive ingestion of silver can cause a rare condition called argyria* (Romans, 1966), a darkening of the skin. Silver is considered to be the least toxic of the heavy metals. The Aquabrite system normally operates within the range 0.01-0.05 mg/L.

The concentration of silver ions cannot be measured with a simple comparator. Its concentration is dependent on the solubility product of its least soluble salt (Glasstone and Lewis, 1965). Silver sulphide is the least soluble of the silver salts but oxidised pool water cannot contain sulphides. The most likely form of silver in pool water is silver chloride.

Ag+ (soluble) + Cl- ----> AgCl (almost insoluble)
*No reports of argyria caused by silver used in oligodynamic applications has been found in the literature

If the chloride ion concentration increases, the solubility of silver chloride decreases (Glasstone and Lewis, 1965). If the temperature of the water increases, the solubility increases. The solubility of silver chloride also increases if salts other than chloride (except sulphide and bromide) are present.

As silver ions can be easily reduced by organic matter, it is necessary to keep them in an oxidised state by maintaining a permanent chemical oxidiser in the pool water.

- Aquabrite Oxidiser -

Aquabrite oxidiser is a special blend of persulphates. Although it is not bactericidal at concentrations used in swimming pools, when copper and silver ions are present a powerful disinfectant is produced in the water.( The disinfectant properties are broad spectrum and residual throughout the pool for up to fourteen days after treatment.)

Aquabrite has an oxidation potential high enough to maintain silver ions in a high oxidation state even to Ag3+ (Zsoldos and Kowalski, 1970). In a similar way, copper is oxidised to Cu3+. This is important for the removal of ammonia from pool water by the following suggested mechanism:

Oxidation S2O8(2-) + 2Cu(2+) ---> 2Cu(3+) + 2SO4(2-)
Reduction 6Cu(3+) + 2NH3 ---> 6Cu(2+) + N2 + 6H+

Organic matter is oxidised but no unpleasant compounds are formed.

The standard dose of Aquabrite is 20mg/L (1Kg per 50,000 litres of pool water) each week in summer, when the pool is in constant use and once per month when not in use. Aquabrite poses no risk to health on the ingestion of pool water, as its final reaction products consist of simple sulphates and oxygen.(Zsoldos et.al., 1970).

- Maintaining Optimum Conditions -

In practice, both copper and silver are lost from the system so that continuous replacement is necessary. Electrolytic generation of copper and silver ions is both practical and convenient and essentially automatic. Copper can be measured with a simple colourimetric test kit, and regulated accordingly. Aquabrite is added manually or as a strong (10%) solution and its concentration in the pool may be easily tested using Palin's DPD test method. A pool test kit utilising DPD No.1 tablets is required for this procedure.

As with any oxidiser, its duration in the pool depends on several factors:

· The organic loading on the pool such as leaves, number of persons using the pool,     chemicals added such as citrates, oxalates, polyelectrolyte pool clarifiers, quaternary     ammonium algicides, etc.
· Rainfall - when the excess water is run off to maintain the correct level of water in the     pool, the active components of the system are lost.
· Backwashing of sand filters, or diatomaceous earth filters results in the loss of sanitiser     from the pool.
· Use of reducing agents for pool cleaning such as metabisulphites, sulphonic acids etc.

A recent review of the literature (Thurman and Gerba, 1988) does not address the mechanism by which the Aquabrite System is able to rapidly disinfect. Researchers have dealt with copper and silver individually or in combination with chlorine (Yahya et.al., 1989) or iodine (Pyle et.al., 1992). Neither chlorine nor iodine is able to oxidise silver to its higher valency state as the necessary oxidation potential to do so must exceed 1.987 volts.

Ag(+) - e <---> Ag(2+)
Ag(2+) - e <---> Ag(3+) *
* It is not known conclusively that the trivalent ion exists in pool water, only that it is theoretically possible.

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ADVANTAGES OF THE AQUABRITE SYSTEM