Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1999-06-21
2001-08-14
Simmons, David A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S764000, C210S167150, C210S416200
Reexamination Certificate
active
06274052
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the ozonation of various pool systems and, more particularly, to such treatment for the inactivation of cryptosporidium and reduction of chlorine concentrations. The treatment processes described herein provide unexpected and surprising results when compared to treatment systems of the prior art.
Swimming pool water differs significantly from drinking water, although almost universally potable water is used to fill pools, initially. Most state health codes for pools mandate a pH between 7.2 and 7.8. In addition, many of those codes also stipulate a minimum, and sometimes a maximum, level for a sanitizer, and recommend values for calcium hardness and bicarbonate alkalinity. The only sanitizers currently permitted are hypochlorous acid, HOCl (customarily referred to as chlorine in the pool industry), and less often hypobromous acid, HOBr (likewise, referred to as bromine). Any future use of “chlorine” or “bromine” herein refers to these acids, and not to the elemental forms of chlorine gas (Cl
2
) or liquid bromine (Br
2
).
With the exception of dichloro-isocyanuric acid, all compounds that produce chlorine or bromine in pool water influence the pH. It is therefore necessary to add either an acidic or caustic substance to maintain the pH. This means that pools have two injection systems: one for the selected sanitizer, and another one for the pH control.
The hypochlorous acid, often referred to as “free chlorine,” can combine with ammonium ions in the water to form monochloramine (NH
2
Cl), and to a much lesser degree dichloramine (NHCl
2
). These chloramines are the main source of irritation for pool patrons, because they have a strong chlorine-like odor, and cause the typical “swimmer's red eye” and itching. While a pool with a concentration of several mg/L chlorine is essentially odor-free, chloramine levels as low as 0.1-0.2 mg/L are noticeable.
Although chloramines are assumed to be the major contaminant fraction, it is known that other chlorinated amines may be present, such other chloramines including the chlorinated byproducts of creatine and creatinine (together, “total chlorine”). Chemical tests are available to measure the concentrations of free chlorine (HOCl), and “total chlorine.” The difference between these two measurements is called “combined chlorine,” and is assumed to consist mostly of monochloramine. Although the various chlorinated nitrogen compounds have quite different properties, they are lumped together by the pool industry under the “combined chlorine” label, mostly because the pool-side test kits cannot distinguish between the various chlorination byproducts. Most of the odor, and the eye and skin irritation at indoor pools is, however, directly related to the presence of mono- and di-chloramines.
Many state codes require operators to initiate procedures such as breakpoint chlorination or the addition of high doses of non-chlorine oxidants, once the combined chlorine level reaches 0.5 mg/L. Breakpoint chlorination is a very slow process, and is usually done after hours or overnight. This means that the operator must start the process after the pool closes, and dechlorinate down to normal levels before the pool re-opens. Pool operators and owners have been looking for ways to reduce or eliminate this costly and labor-intensive procedure.
It should be noted that the chloramine problem is essentially limited to indoor pools. The natural air convection at outdoor pools, coupled with the volatility of the chloramines, ensures that outdoor pools rarely encounter problems with high levels of combined chlorine. Moreover, the tendency towards energy conservation has lead to drastically lowering the amount of fresh air drawn into indoor pool enclosures, and warm air rejected from there to the atmosphere. Elaborate humidity control and heat recovery systems ensure energy savings, but inhibit the venting of the odorous chloramines.
The requirement for maintaining chlorine levels at or above the specified minima is meant to ensure that the pool water remains free of harmful microorganisms. Bacteria, such as
E. coli
or
Pseudomonas aeruginosa
, that may be found in pool or hot whirlpool environments are easily inactivated when the required sanitizer level is continuously maintained. Exceptions are Giardia and Cryptosporidium, which are difficult to inactivate in a pool environment. Since the 1993 Crypto outbreak (drinking water) in Milwaukee, Wis., there have been a number of similar instances relating to swimining pools in Wisconsin, elsewhere, as well as waterparks in Georgia and California. Chlorine has an estimated CT-value of 9600 mg-min/L (where C is average concentration and T is average time) at typical pool water temperatures. With such high concentrations and/or time, it is clear that chlorine is completely ineffective in providing inactivation within a reasonable time span, and at levels tolerable to the bathers.
Ozone has a long history in the treatment of drinking water. However, its use in pool water treatment is much more recent, becoming common in Europe only during the 1960's. The first large US pool ozone system is probably the German DIN-based system at the Peck Aquatic Facility in Milwaukee, Wis. Since then, the number of installed pool ozonation systems has increased rapidly. Most of these systems are, however, fairly small when compared to those required by European codes, such as the German DIN 19623. The typical US installation ozonates a side stream after the filter, with some units treating only 8%-10% of the total filtration flow, and others recommending 25% side stream ozonation for 4 minutes at 0.4 mg/L.
SUMMARY OF THE INVENTION
There are a considerable number of problems and deficiencies associated with pool water treatment systems of the prior art. There is a demonstrated need for an efficient, economical system by which pathologic microorganisms are reliably inactivated and noxious chlorine concentrations safely reduced.
Accordingly, it is an object of the present invention to provide a system and/or method for the ozonation of pool water volumes, thereby overcoming various deficiencies and shortcomings of the prior art, including those outlined above. It will be understood by those skilled in the art that one or more aspects of this invention can meet certain objectives, while one or more other aspects can meet certain other objectives. Each objective may not apply equally, in all instances, to every aspect of the present invention. As such, the following objects can be viewed in the alternative with respect to any one aspect of the present invention.
It is an object of the present invention to provide a pool treatment system whereby reduced levels of ozone can be used effectively to achieve various sanitation and/or oxidation effects.
It can be another object of the present invention to provide a method of ozone treatment of various pool water systems, so as to minimize problems associated with removal of excess ozone.
It can be another object of the present invention to provide an ozonation method and system configuration for use therewith to maximize filtration efficiency.
It can also be an object of the present invention to provide one or more methods for ozone treatment whereby higher average ozone concentrations are maintained over the course of treatment, to enhance effect and increase cost efficiency.
Other objects, features, benefits and advantages of the present invention will be apparent in this summary and descriptions of preferred embodiments, and will be readily apparent to those skilled in the art having knowledge of various water treatment systems. Such objects, features, benefits and advantages will be apparent from the above as taken in conjunction with the accompanying examples, tables, data and all reasonable inferences to be drawn therefrom.
In part, the present invention is a method of using ozone to meet CT values for the inactivation of the cryptosporidium bacteria. The method includes (1) providing a pool filtration system, a total filtr
Hoey Betsey Morrison
Neuman Pools, Inc.
Reinhart, Boerner, Van Deuren, Norris & Rieselbach, s.c.
Simmons David A.
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