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CASCADIAN®
Professional Water
Treatment Products |
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O3
Water Systems, Inc.
17700 147th St SE
Suite F
Monroe, WA 98272
USA
Phone:
360-794-9511
Fax: 360-794-0856
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Ozone Pilot Plant Design:
Why Use
Ozone?
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If you have a reason to apply ozone as part of your water treatment project you may be
required to conduct a pilot study prior to installation of the equipment. In this article
we will discuss many of the reasons to use ozone as part of your treatment project and the
proper
design of an ozone pilot plant. This same information is applicable to ozone
treatment systems. Before consideration of building an ozone pilot plant
you must have a reason to use ozone for the treatment facility under consideration.
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Reasons to
choose ozone over other oxidants such as chlorine in water treatment.
- Reduce Trihalomethane Precursors:
Trihalomethanes (THM's) are a group of disinfection by-products that can
result from treatment of water with chlorine. THM's have been proven to be cancerous.
Ozone will reduce the THM precursors. Oxidizing and filtering organic matter with ozone
prior to chlorination reduces the THM precursors. This in turn reduces chlorine demand as
just enough chlorine is added after ozonation and filtration to provide residual
disinfection through the distribution system. On smaller treatment systems with shorter
distribution lines it is possible to eliminate the need for chlorine all together.
- Ozone is a Powerful Fast Acting Disinfectant and Oxidizer
Ozone is the most powerful disinfectant available for drinking water;
it readily disinfects bacteria and virus and is powerful enough to deactivate the
protozoan cysts giardia and cryptosporidium where chlorine is not.
- Ozone readily oxidizes the troublesome trio - iron, manganese, and hydrogen sulfide.
Ozone also oxidizes many other substances including ammonia, cyanide, nitrite, tannins,
and aromatic hydrocarbons, benzene, toluene, and xylene. Because ozone reacts over 1000
times faster than chlorine contact time for oxidation and disinfection is much less. A
lower contact time requirement significantly reduces contact space requirements and costs.
- Ozone is Safer and Healthier
Ozone is a gas that is created by electricity and cannot be stored or
transported it must be generated on site as it is being used. Because ozone is generated
on site as needed there are no chemicals to purchase, transport or store. Ozone does not
produce the cancer causing THM's and leaves no long term residual oxidant in the water.
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Why use an Ozone Pilot Plant?
- An ozone pilot plant is an excellent decision making tool
When considering full scale implementation of an ozone based
water treatment system you need answers to basic decision making questions
to determine if ozone treatment is the right treatment for your
system.
Questions such as;
- Will ozone treat the problems with your water?
- What other components or additional treatment is needed to
make a complete treatment system?
- What is the correct size ozone system for your system?
- Would using ozone require any facility or infrastructure
changes?
- How much will it cost to purchase and install the equipment
and to train operators?
- What is the long term operating costs?
A well designed ozone pilot plant will give you individual control over
each treatment process variable so you can "zero" in on the exact requirements
to treat the water therefore develop a cost of full scale treatment.
With a proper pilot plant you will be able to determine ozone and chemical dosages
required to treat the water. You will also be able to determine optimal contact time and
optimize filtration variables such as the most effective media, throughput, backwash flow
rate and frequency of backwash.
Piloting will also allow you to account for other treatment variables whether they are
source specific variables such as water temperature, pH, and turbidity or site specific
variables such as humidity.
- Provide Operator Education and training
Although market demand for ozone is growing, it is a rare occasion when
plant operators have pre-existing training or experience with ozone treatment. A pilot
ozone treatment plant gives operators that experience. They will be able to observe the effects
of changing variables in the treatment system and learn how to interpret and
react to them.
- Meet Regulatory Requirements
Regulatory officials will typically require an ozone pilot study when
any treatment is proposed for drinking water and as we have said previously
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Proper
design of an ozone pilot plant - what to consider
When considering the design of a pilot plant thought must be
given to whether the pilot will be of a temporary nature, on site for the duration of the
pilot study only or permanent, left on site for future use. Pilot plants may also be
portable mounted in a self-contained trailer or installed directly in the existing
treatment facility.
Expected Treatment Requirements
After careful analysis of the water and determination of
expected treatment requirements build the pilot to operate within a range that would cover
any expected variables in water quality or flows. Your pilot treatment plant may require
more than ozonation and filtration. You may also need pH adjustment or a softener. If you
need additional treatment steps they must be designed into the pilot, remember that the
goal is to determine exactly what is needed to treat the water.
Pressurized or Atmospheric System
Consideration must also be given to whether the pilot will
be a pressurized or atmospheric system. In a pressurized design the ozonation system is
always under greater than atmospheric pressure. In an atmospheric design the system comes
to atmospheric pressure usually during the contact phase of the treatment process. Each
design will require a different design approach and has different advantages and
disadvantages. For a summary of the differences See Table 1.
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Table 1 |
Pressure
Systems |
Atmospheric
Systems |
Concept |
- The treatment system remains under pressure
during the entire treatment process.
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- The treatment system comes to atmospheric pressure
at some point during the treatment process.
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Cost |
- May be less expensive (especially where the water
to be treated is relatively clean and the volume of water to be
treated is low).
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- May be less expensive where water is very dirty
(especially where the volume of water to be treated is over 10 gpm).
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Suitability |
- Most suitable in residential treatment systems
treating less than 10 gpm and where there is at least an 80 gallon
pressure tank.
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- Suitable for any size treatment system.
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Advantages |
- Simple design.
- Requires only one pump
- Lower system space requirements.
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- Flexible treatment design.
- Can incorporate multiple injection points.
- Easier to control ozone residual levels.
- Can use smaller ozone generator with recirculation
through the contact tank.
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Disadvantages |
- Single injection point
- May require a larger ozonation system for single
point injection.
- The treatment system pump may need to be larger to
insure the pressure differential across the venturi injector is
maintained during the entire pump cycle.
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- More complex design.
- Generally requires larger space for treatment
system.
- Requires more than one pump.
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Flexibility
The pilot plant must be flexible. The
ozone generator in you pilot treatment plant must provide for variable ozone production
and you must have a chart or some other means of determining what the output of ozone is
at various settings, get this chart from your ozone generator manufacturer. The design of
the pilot must also include a means for variation of the contact time. Typical contact
times range from less than one minute to 4 minutes with times as high as 20 minutes.
Filtration - A Vital Part of the
Ozonation Process
The typical ozonation system employs
media filtration after oxidation. A multi-media layered filter with garnet and sand on a
support bed of gravel is very common. Other media filters include BIRM and activated
carbon. Your pilot may employ simultaneous use of different media filters to allow
examination of the effectiveness of different media.
It is of significant advantage to use a clear filter tank. A clear tank provides
dramatic visual evidence of what is going on inside the filter. You will visually observe
what your instruments and gauges are indicating is happening inside the filter such as
performance and things that are not so easily measured such as the results of different
backwash flow rates and media re-stratification.
If treating surface water or ground water under the influence of surface water it may
be necessary to employ a filter that is approved for the reduction of cysts. Cyst
filtration, if required, is a second line of defense if something should go wrong with the
ozone system and may be required as part of the final treatment system design but not as
part of the pilot.
It is important to provide water sample taps for proper measurement and
analysis. Sample tap locations should provide for sampling the raw water, results of
chemical injection, ozone injection, ozone contact time, post each filter and additional
treatment step and the final product.
Functional Tidbits
It is important to provide a proper "work station" for sample testing
and analysis. The work station must provide adequate lighting, space and a power source
for testing, analyzing and computing equipment.
Safety
Safety of personnel must be kept in mind at all times during the ozone pilot
plant design. The pilot plant must be built to meet local electrical and plumbing codes. A
well designed pilot will have clearly labeled all components direction of flow.
How Long Should a Pilot Study Last?
The length of time required for a pilot depends. You must satisfy regulatory
requirements in the district where the pilot will be located. Often the requirement is one
year to cover seasonal changes in the source water supply. If the purpose of the pilot is
to "demonstrate" the speed and effectiveness of ozone a pilot of a few hours or
days may be all that is needed.
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