Academic journal article Journal of Environmental Health

Swimming Pool Disinfection: Efficacy of Copper/silver Ions with Reduced Chlorine Levels

Academic journal article Journal of Environmental Health

Swimming Pool Disinfection: Efficacy of Copper/silver Ions with Reduced Chlorine Levels

Article excerpt

Introduction

Pathogenic micro-organisms such as bacteria, protozoa, and viruses may occur naturally in recreational waters (1,2). In addition, they may be introduced into swimming pools by bathers or through faulty connections between the filtration system and the sanitary sewer (3,4). Proper treatment of swimming pool water is essential for prevention of diseases spread by micro-organisms.

Traditionally, chlorine and chlorine compounds have been used to disinfect swimming pool waters (5). Free available chlorine (FAC) levels of 1.0 parts per million (ppm) or greater are usually maintained to ensure effective control of micro-organisms and to make acceptable the general sanitary quality of swimming pool waters. Although an effective disinfectant, chlorine has several disadvantages. The lifetime of the FAC residual varies with climatic conditions and bather load (chlorine demand). When chlorine reacts with organic compounds and nitrogen compounds present in the water, it forms objectionable by-products such as trihalomethanes (THMs) and chloramines. FAC levels of 0.6 ppm or greater have been associated with irritation of eyes, nasal passages, and skin, as well as with objectionable odors in the pool environment (6). Also, chlorine has a corrosive effect on pool structures, necessitating expensive maintenance work.

Other studies have documented the use of copper/silver ions in conjunction with low levels of chlorine to inactivate micro-organisms (7,8). In addition to controlling bacteria and viruses, metal ions in part per billion (ppb) concentrations are effective in controlling algae and fungi (6,9). Copper and silver ion disinfection has several advantages over chlorine. The ions are chemically stable and do not undergo the destructive reactions of aqueous chlorine, nor do they escape from the water by volatilization as chlorine does. In addition, the metal ions do not form objectionable byproducts such as chloramines or THMs, and they do not exhibit the corrosive properties of chlorine.

Electrolytic generation of copper/silver ions in swimming pool water allows ppb concentrations to be maintained in a convenient and reproducible manner. Regulating the current to the metal electrodes that generate the [TABULAR DATA FOR TABLE 1 OMITTED] ions, as well as the flow rate of water passing between the electrodes, enables precise control of metal ion concentrations. Studies by Gerba and co-workers indicate that the use of 300 to 400 ppb of copper and 40 ppb of silver combined with 0.1 to 0.4 ppm of chlorine is more effective than higher levels of chlorine in limiting a number of micro-organisms, including coliform. These studies suggest a synergistic effect upon micro-organisms subjected to copper or silver ions in the presence of low levels of chlorine (7,10).

To the authors' knowledge, no field studies have been conducted to show the efficacy of copper/silver ions in combination with low levels of chlorine. The primary objective of this study is to demonstrate that, in a municipal swimming pool with a usual bather load, copper and silver ions produced by electrolytic ionization and used with low levels of chlorine provide a level of disinfection for total-coliform bacteria that is equivalent to or better than that obtained with higher levels of chlorine alone. A secondary objective was to determine whether the use of ionization with lower levels of chlorine would adequately control other bacteria, such as heterotrophs. This article reports the results of the bacteriological testing.

Materials and Methods

The Municipal Swimming Pool in the town of Brookline, Massachusetts, was selected as the site for this study. The pool is well operated and maintained by the staff of the Brookline Recreation Department. Residents of the town and surrounding communities use the pool year round, as do organized high school swimming programs. The pool complex was constructed in 1958 and comprises three separate pools: a diving pool, a wading pool, and a lap pool. …

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