Pool Water Sanitizers

The potential for recreational water illnesses (RWIs) within aquatic facilities has pool operators scrambling. According to the Centers for Disease Control (CDC), between January 2005 and December 2006 (the most recent data available), there were 4,412 incidents of RWIs, including 116 hospitalizations and five deaths. According to the CDC, RWIs are spread by swallowing, breathing, or having contact with contaminated water from swimming pools, spas, hot tubs, decorative water fountains, lakes, rivers or oceans. RWIs can cause a variety of skin, ear, respiratory, eye and wound infections. The most commonly reported RWI is diarrhea, which can be caused by germs, such as Cryptosporidium (Crypto), Giardia, Shigella and E.coli. Properly sanitizing pool water is thus of the utmost importance to pool operators. Given the small size of RWI organisms, filtration alone is probably not the answer. There are alternative methods to improve filtration–such as the use of flocculants and polymers–but they can be expensive and impractical. Good water chemistry is the most cost-effective and user-friendly approach to preventing RWIs.

Sanitizer Systems

Most public swimming pools require the use of a chemical sanitizer, or active “oxidant,” such as chlorine, bromine or fluorine to oxidize, destroy, or burn out bacteria, viruses and other organic contaminants. A majority of public-pool operators utilize chlorine because it’s cost-effective and readily available. Its three basic forms are:

1. Liquid chlorine (sodium hypochlorite)

2. Tablet chlorine (calcium hypochlorite)

3. Chlorine gas.

The following is a look at the pros and cons of traditional sanitizer delivery systems, as well as increasingly popular saltwater chlorine generation systems. Liquid Chlorine Liquid chlorine–which ranges from 10- to 12-percent sodium hypochlorite–is available in one-gallon bottles to 52-gallon drums to bulk delivery (hundreds of gallons) via tanker truck. Liquid chlorine is delivered to the pool recirculation system via a liquid feed pump.

Advantages: Relatively low cost and readily available; the ability to increase the feed rate to meet increased demand due to changes in bather load; and ability to prevent maintenance staff from handling the chemical since vendors’ tanker trucks come equipped with a hose and pump to deliver it directly to a storage tank.

Disadvantages: Shelf life–loses its effectiveness over time, so chemical deliveries are more frequent since the stock needs to be rotated. Liquid chlorine also tends to drive up pool water salinity and total dissolved solids (TDS), requiring pool operators to annually drain two-thirds to the full volume of a pool treated with liquid chlorine to keep proper salinity and TDS levels. Tablet Chlorine Tablet chlorine–with its familiar briquette or “hockey puck” shapes–is available in 50- or 100-pound plastic pails, and can be ordered by the pallet load. Tablet chlorine is delivered to the pool recirculation system via an erosion feed process.

Advantages: Long (if not indefinite) shelf life, readily available and easy to store. Local building codes may limit the quantity to be stored, and the tablets should not be stored in the vicinity of petroleum products. Disadvantages: Cost (it requires approximately 1-1/2 pounds of tablet chlorine to provide the same amount of chlorine as one gallon of 12-percent sodium hypochlorite); inability of tablet-chlorine systems to respond to rapid changes in bather load; tendency to overshoot or undershoot the amount of chemical being delivered because chlorinators typically only have two feed rates–it’s either on or off. Calcium hardness and TDS also can build up, requiring an annual draining of a portion of the pool volume. Gas Chlorine Gas chlorine–pure elemental chlorine–is the most effective sanitizer available. It is delivered to the pool recirculation system via an anti-siphon venturi assembly, which draws the gas under vacuum from 150-pound bottles or one-ton cylinders (similar to a municipal drinking water plant), and injects it into the pool water supply line.

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