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INTRODUCTION
Ozone has been instrumental in protecting earth and its life forms for so long that it is
almost incomprehensible. Compared to man, ozone has been around forever. It is not
just a beneficial molecule, but is absolutely essential to this planet we call home. But,
there is much apprehension and misunderstanding regarding ozone use in treating
drinking water. Hopefully the following information can help qualm some of these
concerns
WHAT IS OZONE ?
Ozone (O3) or trioxygen is a molecule composed of three (3) oxygen atoms, temporarily
existing in a very unstable and reactive state. Ozone is so reactive that a suitable
container for storage probably does not exist. Unlike the O2 molecule described in the
next paragraph, this triatomic oxygen defies man’s attempts to store or liquefy it.
Compared to O2, O3 is an extremely active molecule, probably by a factor of 1,000
times and is sometimes referred to as activated oxygen.
Oxygen (O2) is normally thought of as the fraction of air which is utilized in breathing. It
is very necessary and has many common and obvious uses. This regular oxygen or
dioxygen is a relatively stable molecule, composed of two (2) oxygen atoms held
together with a fairly firm double bond. This diatomic oxygen is stable enough to
compress, liquefy and store, yet it is still quite reactive.
Ozone can be visualized as a regular O2 molecule with a very nervous, active, reactive,
excitable, energetic, corrosive and lively O1 atom as a side kick. This monatomic O1
atom does not like to be alone, and near the earth's surface, it refuses to stay with the
fairly stable O2 double bond. It is active and reactive, with energy needing to be
channeled in some useful direction. It will combine with virtually anything on contact, or
at least will try. This active O1 will not stabilize until it can break away from the O2 and
form a stable molecule with something else, virtually any other molecule that is
available. If no other molecule is available, it will eventually unite with another O1 atom
in the same situation, and restabilize as O2.
Ozone is a very strong disinfectant and oxidizer. Any pathogen or contaminant that
can be disinfected, altered or removed via an oxidation process will be affected by
ozone. It is the strongest of all molecules available for disinfection in water treatment,
and is second only to elemental fluorine in oxidizing power. Compared to chlorine, the
most common water disinfection chemical, ozone is a more than 50% stronger oxidizer
and acts over 3,000 times faster. Both chlorine and fluorine are highly toxic chemicals.
On this planet, ozone is a major work horse. From the highest reaches of the
atmosphere to the bottom of the deepest ocean, ozone is a very efficient protector,
provider and recycler. It constantly tries to get rid of one oxygen atom, O3 O2+O1,
which allows it to react with almost anything it encounters.
When this single oxygen atom (O1) forms a tight bond with twin hydrogen atoms, we
have water (H2O), without which this planet would be as barren as the moon. Without
water, life as we know it can not exist.
WHY USE OZONE ?
There is a logarithmic increase in the human population and a zero increase in the
fresh water supply on this planet. Man, by choice, does not necessarily live where the
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best water is and also tends to abuse the water wherever he does live. Besides
contaminating it with various noxins and toxins he produces, man continues to place
more demand, uses and reuses on this existing finite fresh water supply. There is very
little doubt that this tendency will continue world wide. Man's pollution will not cease,
so it will need to be removed to keep our current and future sources of drinking water
safe and palatable.
Ozone treatment is quite efficient and effective in achieving pollution removal, allowing
people more flexibility to use water that exists where they are, or where they want to be.
Our ground water, steams, lakes, rivers and oceans are subject to a wide range of
human caused assaults. Some of these problems are associated with large molecular
structures and unoxidized molecules. Ozone breaks down large and long chain
molecules into smaller building blocks. These smaller molecules are then usually more
biodegradable and less dangerous. In most cases, the smaller molecules are a lesser
pollution problem or impact, as they are more readily recycled or reused in the
environment or removable in a filtration process.
Ozone can be used as a disinfectant, decolorizer, deodorizer, detoxifier, precipitant,
coagulant and for removing tastes. Consequently, the use of ozone should be
considered when there is a need to address any of these problems, and particularly
when there is suspicion of water born pathogens.
Ozone coagulates and precipitates many substances by itself, and is also a reasonably
effective flocculant. Because of this, it can reduce other chemical loading in treatment
facilities.
Ozone production on site, via normal corona discharge, eliminates the problems of
transporting, storing and handling of hazardous and dangerous materials.
For efficiency, ozone is outstanding, as it is the most powerful and effective broad
spectrum microbiological control or disinfecting agent available. As an example, for the
inactivation of Giardia cysts the C t (concentration & time) is about 100 times greater
for free chlorine than for ozone. With viruses the C t is about six times greater for
chlorine than for ozone. For Cryptosporidia, ozone is the recommended disinfectant.
Consequently, with ozone, there is less need to add high concentrations of a long lived
poison to the water you will soon be drinking. When ozone is utilized, the chlorine
need is greatly reduced, as it is then needed only as a way to provide a residual in the
distribution system, at 0.2 mgCl2/L. This minimizes the potential for producing
carcinogenic THMs and helps protect your health.
Ozone is of particular value in water treatment systems because of it's ability to
disinfect without adding other chemicals which may later need to be removed. As with
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other treatment methods, the oxidized by-products of ozonation may need to be
removed by filtration or settling to provide acceptably clean clear water.
Water, being the universal solvent that it is, seldom remains pure water (H2O). Even
the double distilled water used in laboratories contains dissolved traces of other
substances. Ozone will decompose in "pure" water by itself (slower than in air), as well
as reacting with almost anything dissolved or carried in the water.
As clean as rain water is assumed to be, it can usually be improved after ozonation and
filtration. This statement would be especially true in discussing the acid rains.
The following are some common uses of ozone:
algicide - very effective, most if not all
amoebocide - extremely effective, kills all known
aquaculture aid - many uses
bactericide - extremely effective, kills all known
BOD & COD enhancement - quite effective, as this IS real live OXYGEN
coagulant - quite effective
contaminate remover - very selective
decolorizer - usually effective, organic & inorganic, simple & complex,
mineral & carbon
deodorizer - very effective, most are removed
detoxifier - quite specific; some quick, others slowly, some not at all
disinfectant - extremely effective, most if not all biota
dissolved solids - fairly effective, inorganic and organic
flocculant aid - quite effective, fairly specific
fungicide - very effective, all known
hardness - slightly effective with some specific changes
metals - very effectively on some, manganese and iron
oxygenator - extremely effective, particularly wells
particulates - quite effective, inorganic and organic
pesticide - very effective; kills worms, flukes, fish, snails, eggs, larvae, etc.
precipitant - quite effective, extremely useful
precursor reduction - very effective, ie. THMs
softness - somewhat effective, assists and improves specifically
taste - very effective, removes or enhances most
turbidity - quite effective, prepares inorganics & organics for filtration
viricide - extremely effective, kills all known viruses
waste & effluent - quite effective, excellent in a wide range of uses
Ozone treated drinking water can be expected to be:
cleaner clearer colorless nonstaining
odorless palatable safer oxygenated
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In 1995, the World Bank estimated that contaminated water causes ten million people
(10,000,000) to die annually and is the reason for 80% of all illnesses in developing
countries; and that one billion people (1,000,000,000) have no access to clean drinking
water.
Considering all the benefits and lack of drawbacks, ozone is a good choice.
HOW IS OZONE CREATED ?
In nature, the most common and vivid production of Ozone is with lightning discharges.
The fresh clean aroma after a lightning storm or a rain shower is ozone.
In the presence of oxygen, nearly any high energy source can and does produce
ozone. The two sources we relate to best are electrical and radiation energy. Any
energy source powerful enough to break the firm O2 bond to form O1 can produce
ozone. The ozone created may disassociate quickly, but none the less, it is produced.
The energy of a water fall or pounding surf will locally produce trace amounts of ozone,
which generates the fresh aroma associated with these areas. In mild concentrations
the odor is extremely fresh, somewhat garlicky and quite pleasant. The process of
photosynthesis in a leaf, although low energy, produces O1, again allowing for pleasant
refreshing air in a forest or greenhouse. In an office, the clean smell around a Laser
printer is ozone.
Ozone is a naturally occurring molecule. It is Mother Natures’ natural cleanser. She
produces ozone wherever it is needed for protection, recycling and clean up. The
ozone layer of the outer atmosphere shields earth from heavy doses of ultraviolet light
emissions from the sun, protecting all forms of life. Destruction of, or even significant
reduction of, this stratospheric ozone layer will have dire consequences for most life
forms on earth , not just mankind.
In our lower atmosphere the sun continuously produces ozone in small amounts.
Ozone seems to be one of the automatic defense mechanisms of Earth itself, as well as
it’s best and strongest natural cleanser. The more pollution man dumps into the
atmosphere, the more ozone Mother Nature produces to clean it up. In attempting to
clean up this smog, the amount of ozone produced photochemically by nature is so
precise (as needed-where needed), that scientists use this exact concentration of
ozone as the index for the total level of pollution. Unfortunately, the scientists forget to
footnote that ozone is the "index", so the public is left with the impression that the
ozone is actually causing the polluting, rather than being an induced product of the
pollution. In heavily polluted areas, the sunlight passing through the air pollutants can
produce ozone concentrations so high that it can become a pollutant and hazard also.
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HOW DO WE PRODUCE OZONE ?
Since ozone cannot be stored or conveniently purchased by the gram, pound, gallon or
ton, it must be produced on site as needed, where needed and when needed.
We have discovered or devised many ways to produce ozone.
All of the following processes can be used:
Electrical Discharge - Corona Discharge.
This process seems to be the safest, most effective, economical and dependable
means of controlled ozone production. It involves discharging high voltage electricity
across a gap through which filtered dry air or pure oxygen is flowing (a glorified spark
plug). Corona discharge is somewhat like miniature lightning in a completely controlled
and enclosed environment. Many sizes and shapes of these commercial ozone
generators are available, from small portable ½ g/hour units to large 50 kg/hour
models. Where ozone is used in the water treatment industry, the corona discharge
method of production is used almost exclusively.
Electrolytically - Electrolysis of an Acid.
This is a very easy way to produce ozone with very simple equipment. It could have
great appeal in unsophisticated and remote locations, but is a seldom used method of
producing ozone for drinking water treatment. At present, this process is probably 2 to
5 times more expensive than Corona Discharge production. It also involves
transporting acids to sites of ozone production, and potentially problematic disposal of
containers or other materials. The development of new electrodes and membranes
should soon reduce the cost and maintenance problems of these systems. Other
oxidants can also be produced via these methods.
Photochemically - Ultraviolet radiation (UV light).
Sunlight, with its warming and healing effects can and does produce ozone.
Although sunlight produces ozone in the upper atmosphere, which is not where it is
needed for drinking water treatment, the photochemical principle can be applied to
produce ozone where it is needed. Both black lights and UV bulbs generate
wavelengths necessary to produce ozone from oxygen sources. UV can be a very
handy, versatile and unique tool for some applications and situations. In effect, they
produce ozone at short range in clear water or air, as oxygen is present.
Many UV bulbs are available, with wavelengths within the appropriate range of 180 to
254 nm (nano meters). However, with currently available technology, these bulbs are
not an economical or efficient way to generate ozone, producing only up to 0.3-0.4% by
weight. Although X-ray machines or microwave ovens have sufficient energy, their
frequencies are not right for efficient ozone production.
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Radiochemically - High energy irradiation of oxygen will produce ozone. This is not
yet used commercially in potable or waste water treatment, because it is quite technical
and very political. In the future this may conceivably be a good use of excess
fissionable material, but currently there is much more fear of radiation than of bad
water. The excess fissionable material is thus considered to be just a hazardous waste
instead of a potentially valuable resource.
Other & Misc. - Various other methods, such as reacting yellow phosphorous with
oxygen, can produce ozone. As the demand for ozone increases, more sources and
techniques for producing it economically will be explored.
WHAT HAPPENS TO OZONE ?
Ozone is quite short lived in water, enduring only about 20 to 30 minutes in distilled
water at 20 C and not nearly that long if contaminants are present.
When ozone is destroyed or self destructs, it can revert back to oxygen (2O3 3O2).
Since it required energy to create ozone, destruction back to O2 releases energy as an
exothermic reaction of 68,800 calories.
Destruction methods for excess ozone (off gasses) are adsorption, catalytic, chemical,
dilution, thermal and full utilization. Ozone is usually considered fully utilized or
destroyed when the off gas is 0.12ppm for outdoor venting to the atmosphere or
0.10ppm by volume (0.002g/m3
) for indoor venting.
The following are brief descriptions of some ozone destruction mechanisms:
ADSORPTION is normally accomplished with an activated carbon filter. This
is not highly recommended, as theoretically it can produce heat, which with
carbon dust, in the presence of the oxygen is potentially dangerous.
CATALYTIC conversion is usually accomplished with metals and metal oxides at
temperatures from ~85 to ~160 F (~30 to ~71 C)
CHEMICAL destruction of off gas is accomplished by scrubbing.
DILUTION by direct venting into the atmosphere on a large scale is not presently
considered an option, as it once was. Mechanical dilution via forced venting is
sometimes acceptable.
THERMAL destruction takes advantage of ozone's self degradation back to
oxygen at various temperatures. The rate of destruction is approximately as
follows:
In dry air: ~20 to 100 hours at room temperature, 70 F or 21 C
~10 to 115 minutes at 120 F or 49 C,