Tassal Tasmanian Salmon, an Australian salmon farming company, backed away from plans to dump treated wastewater from salmon pens into...
Ozone does not need to be complicated in order to treat
small water systems. A small water system consists of one or multiple
households on well, spring or rooftop water. Treatment means removal of iron,
manganese and hydrogen sulfide to below the U.S. Environmental Protection
Agency (EPA) acceptable levels including bacterial control.
Ozone consists of three atoms of oxygen (O3) and is a
powerful oxidizer and disinfectant. It must be generated on site since it
reverts to oxygen (O2) within minutes. Ozone, which works faster and is more
powerful than chlorine, adds nothing to the water except pure oxygen. Chlorine,
on the other hand, can produce a carcinogenic byproduct called trihalomethanes
(THMs) when combined with organic matter found mostly in surface waters. Its
objectionable odor is another disadvantage to those who expect their well or
spring water to taste and smell sweet and natural.
In traditional applications, ozone is produced by the corona
or high voltage spark method. In order to be effective, the corona-type ozone
requires a dry filtered air. Its longevity depends on this because moisture
creates nitric acid, thus decreasing ozone output and corroding the equipment.
If the air dryer fails, so will the entire system. A corona ozone injection system
uses lots of electricity, is complex and, therefore, not very reliable for the
average homeowner or small system operator. In addition, applications of corona
ozone must be done carefully as high concentrations of ozone literally can
destroy common holding tanks and distribution systems. When using corona ozone,
stainless steel tanks are recommended as well as an activated carbon filter to
remove the excess ozone before the water enters the distribution system. This
complicated corona method produces large amounts of ozone and uses a relatively
short contact time with the water. For these reasons, corona ozone use is
recommended for large commercial applications where it can be monitored on a
An alternative technology has been developed using small,
safe levels of ozone produced by the ultraviolet (UV) light method. With this
technology, low levels of ozone are continuously introduced into an atmospheric
holding tank. If the approach to water treatment would be by injection or single
pass, this method would be insufficient to perform its oxidation and
disinfection tasks. Since this system bubbles ozone into the tank water 24
hours per day, it not only is extremely efficient but also cost effective due
to its low energy consumption of 55 watts, lack of an air dryer and
compatibility with tank materials.
Unique to this system is a filter module that is suspended
on a stainless steel chain and actually filters the entire contents of the
holding tank. The water moves through the 100-square-foot filter at 10 gallons
per minute or 14,000 gallons per day, thus removing all of the oxidized
particulates and preventing debris from accumulating on the bottom of the tank.
When the filter becomes loaded, it is washed off and returned to the tank, eliminating
the need for costly filter replacements. This unique in-tank filtration also
eliminates filter backwashing and its associated water loss.
An optional piece of equipment used with this system is a
mixer/injector that diverts the ozone from the tank and injects it into the
incoming water. This injection takes place only when the pump is in operation
and the tank is being refilled with the raw water, thereby pretreating the
water before its introduction into the tank.
This type of system is capable of removing all objectionable
levels of iron, manganese and hydrogen sulfide. In severe cases, it may be
necessary to use two tanks in series and to treat each tank individually. For
instance, in a water supply containing 60 ppm of iron, the iron was successfully
removed using this dual tank set-up. Generally speaking, tanks need to be sized
at four times the daily water usage. An average family of four uses
approximately 350 gallons of water per day, so the minimum tank size should be
about 1,500 gallons or larger. If possible, take irrigation water off the
wellhead before the tank and use the tank water for household use only. Use one
system per each 10,000 gallons to be treated. Multiple systems can be used in
When considering this technology for contaminant removal, it
is important to know the volume of water used per day as well as the
contaminant levels. Contaminant levels are best shown by a water analysis
performed by an independent laboratory. Ozone readily oxidizes both iron and manganese
but will oxidize all the iron before attacking the manganese. This is a
phenomenon that will affect the prescribed dosage and contact times and is
another reason to have a thorough knowledge of the water that will be treated.
Also, water with a high organic content such a tannin will adversely affect the
ozone's ability to act on inorganic material, further affecting dosages and
An additional benefit of this technology is the aeration
process. A system such as this is able to remove undesirable gasses and their
effects from the water because it uses ozone in combination with aeration. For
instance, when low pH is attributed to carbon dioxide gasses, which are removed
in the aeration process, the pH levels then are elevated. Due to the aeration
process, this system acts on all dissolved gasses contained in the water
including radon and methane. Another benefit applies when a customer has an
existing holding tank with no particular water problem. This system can be used
to prevent stagnation, algae growth and bacterial contamination.
This technology also is appropriate for use in surface water
and/or rooftop catchment systems. Under surface water conditions, a sand filter
is suggested to remove turbidity (dirt) and debris before the water enters the
tank. The ozone then is able to expend all of its energy on killing bacteria.
When treating surface water, it is advised that a secondary method of
disinfection should be added as back-up protection, since you are dealing with
water subject to fecal coliform and other primary health contaminants. If
Giardia or Cryptosporidium (protozoa) are of concern, do not rely on ozone
technology. Instead, use a 1 micron absolute filter for removal after the tank
treatment. When treating other contaminants in well water such as total
dissolved solids, use the in-tank ozone system before both water softeners and
reverse osmosis units to keep resins and membranes clean.
Maintenance is a major consideration in any type of water
treatment equipment. Maintenance required for this system is minimal. It
consists of cleaning the filter approximately every three to six months by
pulling it from the tank and hosing off the accumulated debris. The ozone
diffuser also is cleaned at the time by dipping it into muriatic acid. The
ozone-producing UV light needs to be changed every 18 to 24 months if treating
secondary contaminants or every 12 months if used for bacterial control.
Installation is another important consideration when dealing
with water treatment equipment. This ozone system normally will take less than
two hours to install, and its installation is relatively simple. The ozone
generator is mounted beside or up to 200 feet from the holding tank. Tubing
that carries the ozone gas runs from the generator, up the side of the tank and
down inside the tank where it connects to the filter module. The filter module
is suspended from the tank top on a stainless steel chain and contains the
diffuser that bubbles ozone up through the tank water. The mixer/injector is
mounted into the inlet pipe to the tank.
Using atmospheric vented holding tanks/cisterns to apply
ozone is a simple, viable, cost-effective and reliable method of water
treatment for problem well water. Water treatment professionals worldwide have
used this technology successfully since its development in 1990.
Your customers not only are expecting to have enough water
supplied from their water source, but they also demand that it is of superior
quality. Ozone's technology coupled with such treatment as filters or
softeners can fulfill this expectation.