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Chemical commentary.

Re: "The Science of Sanitization" (8/22/03):

Bromine (p. 66)

* Bromochlorodimethylhydantoin BCDMH) does not split into hypobromous acid (HOBr) and bromamines. Upon hydrolysis, it readily forms hypobromous acid and slowly releases chlorine as hypochlorous acid.

* The chlorine in BCDMH does not serve as an oxidizer because it reacts rapidly with bromide ions in pool or spa water, forming HOBr.

* BCDMH tablets are not used to a significant extent in outdoor pools because bromine cannot be effectively stabilized against decomposition by sunlight.

Chlorine (pp. 66, 68)

* Calcium hypochlorite does not result from chlorine gas passed over sodium hydroxide. Instead, it is produced in a multistep process employing calcium hydroxide, chlorine and sodium hydroxide.

* Lithium hypochlorite is not chlorine bubbled through lithium, sodium and potassium sulfates. The exact process is described in an article by J.A. Wojtowicz in the Encyclopedia of Chemical Technology, 4th ed., vol. 5, pp. 932-968, 1996.

* There is no problem with sprinkling (i.e., broadcasting) chlorine sanitizers such as calcium and lithium hypochlorites on the surface of the water. This is done when bathers are not in the pool. Furthermore, these products dissolve quickly; therefore, there is no danger of damage to equipment.

* Hydrolysis of hypochlorite ion (C10- + H20 D HOCI + OH-) temporarily increases pH. However, the effect, which is significant (-0.2 pH units) with a shock dose, will disappear when the chlorine dissipates (Wojtowicz, JSPS1, vol. 3, no. 2, p. 34, 1999).

* Trichlor floater feeders are not problematic. The dissolution rate is too slow to create a corrosion problem. For example, three 3-inch tablets require more than one week to completely dissolve.

Ionizer (pp. 68, 70-71)

* The ionization process does not turn calcium carbonate into calcium bicarbonate. This would require acid.

* The dissolved calcium in the water does not attract calcium in the carbonate form, slowly reducing existing scale buildup

* In fact, ionizers are themselves subject to scaling. Consequently, the polarity of the electrodes is reversed periodically to alleviate the problem.

* Copper ions are not attracted to calcium in the water, forming a semisolid that is caught on the filter. Based on solubility product calculations, copper ions precipitate as copper oxide (CuO) at typical pool pH (Aquatic Chemistry, 3rd ed., pp. 396-399).

UV light treatment (p. 70)

* The oxidation that occurs when hydrogen peroxide is exposed to UV light is due to formation of hydroxyl radicals. However, the effect is only local (i.e., in the immediate vicinity of the UV lamp) and the hydroxyl radicals rapidly recombine, forming oxygen and water, limiting oxidation of organic matter. While some oxidation of amino acids takes place, the ammonia byproduct does not undergo oxidation (Wojtowicz, JSPS1, vol. 4, no. 1, p. 9, 2001).

* Oxidation-reduction (redox) potentials are not speed ratings indicative of disinfection rates. Redox potentials measured in volts represent the thermodynamic tendency for a reaction to certain products.

* Because hydrogen peroxide is a poor disinfectant and algicide, the bulk water will lack an effective sanitizer residual.

* Hydrogen peroxide does not dissolve DE.

Ozone (p. 71, 72)

* UV ozonators are not effective for pool or spa sanitation because of the very low concentration of ozone they produce (Wojtowicz, JSPSI, vol. 4, no. 1, p. 41, 2001).

* Despite ozone's high oxidation potential, it reacts very slowly with some bather contaminants, e.g., urea, which is the main bather contaminant.

* European practice (DIN 19643) employing full stream ozonation (1.5 wt. % 03 in feed gas, ~1 ppm dissolved O3, [greater than or equals to] 2 minutes contact time) in conjunction with flocculation, filtration, a water purge, an effective GAC filter (i.e., biologically active) and chlorination increases bather contaminant removal by approximately 20 percent (over-chlorination-flocculation-filtration) using a sixhour turnover rate. Recovery of capital costs typically takes about eight years.

* Because North American practice uses slipstream ozonation (typically 10-50 percent), does not employ flocculation or a water purge and may not have an active GAC filter, bather contaminant removal will be significantly lower, reducing cost effectiveness.

John A. Wojtowicz

Chemical consultant



Editor's note: "The Science of Sanitization" was written by a professional journalist who does not specialize in this industry. She was trying to paint a broad picture of the topic and did not intend it as a scientific piece. Pool & Spa News regrets an3, confusion that may have resulted.
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Title Annotation:Letters
Author:Wojtowicz, John A.
Publication:Pool & Spa News
Date:Nov 7, 2003
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