American Water announced the recipients of the 26th annual James V. LaFrankie Scholarship Awards. The...
Today's Lesson: Back to Basics
What is Ozone?
Ozone is not some magical gas from the planet "O."
Ozone is an extremely active form of oxygen. Lightning is nature's ozone
generator. Every time you see lightning you are witnessing the generation of
ozone on a massive scale. If you have ever noticed a clean/different smell
after a lightning storm, then you have smelled the cleansing effects of ozone.
The chemical sign for ozone is O3, which contains +2 and -1
oxygen. The triatomic, bipolar characteristics are what make ozone an extremely
strong disinfectant, oxidizer and micro-flocculent. Ozone is detectable by most
properly functioning olfactory senses (your nose) at 0.05 ppm. Ozone reverts
back to oxygen quickly, which means that maintaining a residual can be
difficult. This means that the detrimental effects of a long-lasting chemical
such as chlorine are eliminated. Maintaining ozone residual is necessary only
in a limited number of applications, which are uncommon to most domestic water
Ozone is the most powerful natural oxidizer and disinfectant
of practical use that we know. It is safe and easy to use and can be applied by
using existing water treatment equipment and technology.
Ozone Unit (Ozonator)
Ozone is produced by two practical methods.
--Corona discharge (CD), the spark method, is similar to
lightning discharge. The CD method involves three parts.
--Anode. The center electrode where the high voltage
positive charge is applied.
--Cathode. The outer conductor (negative charge) that draws
the arc/electrical discharge from the Anode.
--Dielectric. The insulator between the anode and cathode.
--Ultraviolet light (UV). Ozone is produced by the
interaction of air and UV radiation between the bulb and the inside of the
shield. The UV ozone generation method is not to be confused with an in-line
water flow UV light.
How Does Ozone Work?
To understand how ozone accomplishes disinfection you must
first understand what ?oxidation" means. Oxidation means to
--change the form by combining with or adding oxygen and
--increase the valence of an element by the loss of
Valence is defined as the combining power of an atom as
shown by the number of its electrons that are lost, gained or shared in the
formation of chemical bonds.
Ozone kills bacteria by oxidizing the organic material in
bacterial membranes, which weakens the cell wall and leads to cellular rupture.
This exposes the organism to the external environment, which causes almost
immediate death of the cell. The process is similar to being cut open by a
Soluble divalent ferrous iron is oxidized rapidly to trivalent ferric iron,
which hydrolyzes and precipitates as ferric hydroxide. This insoluble form of
iron then absorbs some polar organics in the coagulation process and can be
easily removed with filtration.
Odorous hydrogen sulfide, which is not filterable, is quickly converted into
elemental sulfur, which is easily filtered. A portion of the sulfur is
devolatized and off gassed. The iron or sulfur bacteria are killed (as
described above) quite rapidly (if enough ozone is injected) then removed via
Manganese is oxidized and filtered in the same manner as
iron and/or sulfur.
In short, ozone acts as a magnet for iron, sulfur, manganese
and similarly charge particles. It brings them together forming a larger particle
that is removed easily by filtration.
How Much Ozone is Necessary?
This probably is the most debated question in the industry.
What is the correlation between commercial/industrial (C/I) and domestic ozone
treatment? There is no correlation.
In other words, the amount of ozone required to oxidize
iron, sulfur and manganese in domestic applications is far lower than the
amount required to oxidize bacteria or VOCs or for C/I applications.
--C/I ozone equipment is large; construction materials are
built for extreme ozone resistance; contact time is longer; the ozone residual
is far greater; safety precautions and equipment are extensive; and the initial
and maintenance costs are high.
--Domestic ozone equipment is small; built of standard
materials found commonly in home water treatment equipment; has short or no
contact time; extremely low or no residual; requires virtually no safety
precautions are required since the ozonators are low production; and produces
either no or low residual.
The rule of thumb for sizing is
--Iron, sulfur, manganese oxidization = 0.5 grams/hr (500
ppm) per 5 gpm and 5 ppm iron, sulfur and manganese.
--Killing bacteria (100 cfu) = 1 gr/L gpm (no other ozone
demand can be present).
Which Parts Typically Are Used in an Ozone System?
The parts needed to complete an ozone system will depend on
the application. The list of applications is quite extensive, so we will choose
the domestic well water application as this example.
Once the ozonator has been selected you must then select the
--type of ozone injector (ozone pump or venturi),
--air dryer (depends on the hours of water usage),
--automatic ozone unit actuation switch and
The above items will be discussed in detail in the next
article, "Well, Ozone Again," featured in the December issue.