Here is what appears in Volume 4 Number 1 of the Journal of the Swimming
Pool and Spa Industry:
General:
An Introduction to the Journal
Articles:
John A. Wojtowicz
Chemcon
Survey of Swimming Pool/Spa Sanitizers and Sanitation Systems
Basic information on the various sanitizers and sanitation systems used
in swimming pools, spas, and hot tubs is discussed from the standpoint of
mode of action, disinfection, algae control, oxidation of contaminants,
compatibility with ancillary chemicals, and cost. The main chemical sanitizers
used in swimming pools and spas are calcium, sodium, and lithium hypochlorite,
chlorine gas, chloroisocyanurates, and bromochlorodimethyl–hydantoin.
Chlorine is the lowest cost and by far the most widely used sanitizer because
it performs all three sanitizer functions effectively, i.e., disinfection,
algae control, and oxidation. Use of bromine is limited primarily to indoor
applications because it cannot be effectively stabilized. Systems employing
ozone, polyhexamethyl biguanide, metallic ions (copper, silver, or zinc),
persulfate–type oxidizers, UV–hydrogen peroxide, and electrolyzers
are used to a small extent. In addition they do not offer an effective alternative,
significant improvement in performance and/or cost effective advantage to
chlorine.
John A. Wojtowicz
Chemcon
Chemistry of Nitrogen Compounds in Swimming Pool Water
Nitrogen–containing impurities (e.g., ammonia, amino acids, creatinine,
uric acid, etc.) introduced into swimming pools by bathers react with free
available chlorine to form combined chlorine compounds. Because these compounds
do not readily hydrolyze to hypochlorous acid, they are poor disinfectants.
In effect, these combined chlorine compounds adversely affect disinfection
by consuming free available chlorine. Ammonia is readily oxidized by free
chlorine by the process of breakpoint chlorination. Amino acids are also
decomposed by excess free chlorine although at a slower rate. Creatinine
is similarly decomposed but the process is very slow. Ammonia derived chloramines
are inherently unstable in the presence of sunlight because they absorb
ultraviolet light. Indeed, monochloramine although stable in the absence
of sunlight and free chlorine, is largely oxidized (~67%) to elemental nitrogen
in the absence of free chlorine and the presence of sunlight. It is worth
noting that it is urea and not ammonia that is the major nitrogen–containing
bather contaminant in swimming pools and spas. Surprisingly, urea does not
itself form combined chlorine and also does not appear to affect disinfection.
However, urea has to be destroyed by oxidation because it is a nutrient
for bacteria and algae and a source of ammonia chloramines. Oxidation of
urea by free chlorine is a slow process that gives rise to transient ammonia
chloramines (e.g., di– and trichloramine). Oxidation of other organic
nitrogen compounds by chlorine also forms transient ammonia chloramines.
John A. Wojtowicz
Chemcon
Use of Ozone in the Treatment of Swimming Pools and Spas
Although ozone is an effective disinfectant, it cannot be used as a
primary sanitizer because of its volatility, toxicity, and short lifetime.
Since ozone is unstable and hazardous, it has to be produced on–site
from air by ozone generators (ozonators). Commercial units employ ultraviolet
light (UV lamps) or electrical discharge (i.e., corona discharge or CD).
UV ozonators produce very low concentrations of ozone compared to CD ozonators,
i.e., <0.1 vs. ~1.5 wt. %.
Ozone reacts very slowly with bather contaminants such as ammonia, monochloramine,
urea (the main contaminant), and creatinine, even at high ozone and contaminant
concentrations. Both chlorine and bromine are more effective than ozone
in oxidation of these contaminants. The very low ozone concentrations produced
by UV ozonators makes them even less effective than CD ozonators in oxidation
of bather contaminants.
A number of UV ozonators have been evaluated and found to be unsuitable
for pool or spa use. Although UV ozonator manufacturers typically claim
lower chlorine consumption (typically 60 to 90%) and the ability to operate
pools and spas at lower chlorine concentrations, no independent data are
provided to support these claims.
In Europe, CD ozone is used in an integrated system such as the German–designed
ozone–granular activated carbon (GAC) process that employs flocculation,
sand filtration, ozonation, GAC filtration, and chlorination and also includes
a water purge. In DIN (German Industry Standard) based installations, the
reduction in chemical oxygen demand (COD) of the water (other than ammonia
and urea) is improved by 20% over the same process without ozone/GAC. The
GAC filter apparently plays a key role by providing chemical and biological
destruction of bather contaminants that are not oxidized by ozone. Indeed,
the GAC filter may account for a greater reduction in bather contaminants
than ozone itself. Although ozone/GAC filtration reduces operating costs
by 20%, this system is cost effective only for large heavily used pools.
In North America variations of the ozone/GAC process are employed that treat
only a portion of the water resulting in lower COD reductions than obtained
using DIN–based systems.
John A. Wojtowicz
Chemcon
The Carbonate System in Swimming Pool Water
The carbonate system in swimming pool water is described, and formulas
are given to calculate the various components of the system.
The three techniques for carbon dioxide determination found in Standard
Methods (APHA 1995) are also discussed, and are compared to the more complex
equations, with examples.
The carbonate system in swimming pool water consists primarily of bicarbonate
ions with small concentrations of carbonate ions that are the alkaline constituents.
The water also contains low concentrations of dissolved carbon dioxide (<10
ppm) and very small concentrations of carbonic acid (<0.2% of the total
carbon dioxide). The combination of the alkaline and acidic components forms
a buffer system that helps stabilize pH. Alkalinity (in the form of bicarbonate
and carbonate ions) and calcium ions at appropriate concentrations are necessary
in order to ensure saturation of swimming pool water with respect to calcium
carbonate – thus avoiding etching of plaster surfaces. Etching in undersaturated
water occurs by reaction of hydrogen ions with calcium carbonate on the
surface of plaster, forming soluble calcium and bicarbonate ions. The hydrogen
ion concentration is a function of the relative concentrations of the various
components of the carbonate system. Etching is not due to any inherent aggressiveness
of the water or the presence of certain aggressive species but rather to
the fact that the water is not saturated with respect to calcium carbonate.
Etching is avoided by maintaining a slightly positive saturation index,
i.e., water that is slightly oversaturated with respect to calcium carbonate.