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February,
2001
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Volume
1, No. 1
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Inside
this Newsletter 1.
Membrane Technology 2.
New regulations favor... 3.
Disinfection Comparison 4.
On line 5.
Thought of the month 6.
Anyone know the answers? 7.
Chemical feeders 8.
News from over there 9.
All phosphates are the same! 10.
The Bidding Process
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Membrane
Technology
Membrane technology
is a thin layer of semipermeable materials capable of separating
substances when a driving force is applied across the membrane.
Its technology, once only considered viable for desalination, is
being increasingly employed for microorganisms and particulate material,
and organic matter removal. As such, membranes make claim to color
(from organic matter), taste and odor problems in one non-chemical
treatment without formation of detrimental by-products (DBPs). As
new advancements continue to be made, operating costs continue to
decline. For small systems, this technology becomes very attractive
because capital costs (based on dollars per unit volume of installed
treatment capacity) do not escalate rapidly as plant size increases.
Additionally, for ground water sources who do not need pretreatment,
membrane technologies are relatively simple to install requiring
little more than a feed pump, membrane modules, and some holding
tanks.
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Existing membrane
technologies already show great promise for meeting many of the
current and anticipated regulations. The Surface Water Treatment
Rule (SWTR), the Groundwater Disinfection Rule, and Disinfectants/Disinfection
Byproduct rules have all combined to increase interest in membrane
filtration. More and more professionals are being encouraged to
consider these unconventional treatment processes as replacement
or in conjunction with conventional treatments.
Membrane classification
standards vary industry wide so what one supplier sells as an ultrafiltration
membrane, another supplier calls a nanofiltration membrane. It is
far better to look at pore size, molecular weight cutoff, and applied
pressure needed when comparing systems.
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Microfiltration
Microfiltration
(MF) is defined as a membrane separation process with a pore size
of 0.03 to 10 microns, molecular weight cutoff of > 100,000 daltons,
and a relatively low feedwater operating pressure of approximately
15-60 psi. Materials removed by this type of system include sand,
silt, Giardia lamblia and Cryptosporidium cysts, algae, and some
bacterial species.
MICROFILTRATION
IS NOT AN ABSOLUTE BARRIER TO VIRUSES AND REQUIRES DISINFECTION.
MICROFILTRATION REMOVES LITTLE TO NO ORGANIC MATTER AND REQUIRES
PRETREATMENT TO DO SO TO PREVENT MEMBRANE FOULING. PREFILTERS ARE
NECESSARY TO REMOVE LARGE PARTICLES THAT PLUG THE INLET. ADDITIONALLY,
COAGULANTS AND POWDERED ACTIVATE CARBON HAVE BEEN USED TO ENHANCE
REMOVAL OF VIRUSES AND DISSOLVED ORGANIC MATTER. IT MAY BE NECESSARY
TO ADJUST FEEDWATER BY CHEMICAL FEED PRIOR TO MEMBRANE FILTRATION
IN ORDER TO MAINTAIN pH WITHIN THE RECOMMENDED OPERATING RANGE FOR
THE MATERIAL USED.
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Ultrafiltration
Ultrafiltration
uses a membrane pore size of approximately 0.002 to 0.1 microns,
and molecular weight cutoff of approximately 10,000 to 100,000 daltons,
and an operating pressure of 30 to 100 psi. Ultrafiltration removes
all microbiological species removed by microfiltration as well as
some viruses (not all), humic materials, and many water soluble
organics. Does not require coagulant or flocculating chemicals nor
pH adjustment, but disinfection back up is recommended. Required
pretreatment is normally very low, but it may be necessary to adjust
pH of influent to allow its filtration.
FOULING IS THE MAIN PROBLEM WITH ULTRAFILTRATION THUS MAINTENANCE
BECOMES A CRITICAL FACTOR WITH THIS TECHNOLOGY. AS WITH ALL MEMBRANES,
WATER CONTAINING DISSOLVED OR CHELATED IRON OR MANGANESE IONS MUST
BE TREATED BY AN ADEQUATE OXIDATION PROCESS (SUCH AS AERATION, pH
ADJUSTMENT TO > THAN 8.0, OR ADDITION OF STRONG OXIDANTS SUCH AS
CHLORINE, CHLORINE DIOXIDE, OZONE, OR POTASSIUM PERMANGANATE),IN
ORDER TO PRECIPITATE THESE IONS PRIOR TO ULTRAFILTRATION.
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Nanofiltration
Nanofiltration
(NF) has a nominal pore size approximately 0.001 microns and a molecular
weight cutoff of 1,000 to 100,000 daltons. Operating pressures are
necessarily higher than MF and UF from 90 psi to as high as 150
psi. These systems remove all cysts, bacteria, viruses, and humic
materials.
NANOFILTRATION REMOVES ALKALINITY THEREBY PROVIDING FINISHED WATER
WHICH MAY BE CORROSIVE. NANOFILTRATION ALSO REMOVES HARDNESS AND
THEREBY REQUIRES PRETREATMENT OF WATER SUPPLY TO AVOID PRECIPITATION
OF HARDNESS IONS ON MEMBRANES.
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Reverse
osmosis
Reverse osmosis
systems are compact, simple to operate, and require minimal labor
making them suitable for small systems and systems with a high degree
of seasonal fluctuations in water demand. Reverse osmosis removes
almost all inorganic species as well as radium, larger organic molecules,
pesticides, cysts, bacteria, and viruses. Post disinfection is recommended
to ensure safety.
REQUIRES HIGH CAPITAL COSTS. MANAGING THE WASTEWATER BRINE SOLUTION
CAN BE DIFFICULT. HIGH LEVELS OF PRETREATMENT IS REQUIRED IN SOME
CASES. MEMBRANES ARE PRONE TO FOULING. PRODUCES THE MOST WASTEWATER
AT 25-50% OF FEED. SPECIAL NOTE TO HOME CONSUMERS ON REVERSE OSMOSIS
SYSTEMSı COST: MANY SUPPLIERS OF SUCH SYSTEMS FOR HOME USE SELL
THESE SYSTEMS WITH A NEVER ENDING CONTRACTUAL AGREEMENT WHEREBY
THE SYSTEMS ARE CONTINUOUSLY SERVICED BY THE SELLERS. AS SUCH, CONTRACTS
OF $15 TO $20 PER MONTH ARE NOT UNUSUAL FOR A SYSTEM WHICH MAY COST
$600-$1000. IN 2 TO 4 YEARS THE SYSTEMS ARE PAID FOR AND ALL SUBSEQUENT
PAYMENTS WHICH MUST BE CONTRACTUALLY MADE ARE FOR SERVICE ONLY.
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Inside
this Newsletter 1.
Membrane Technology 2.
New regulations favor... 3.
Disinfection Comparison 4.
On line 5.
Thought of the month 6.
Anyone know the answers? 7.
Chemical feeders 8.
News from over there 9.
All phosphates are the same! 10.
The Bidding Process |
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Drinking
Water Disinfectants Comparison
a)
Sodium hypochlorite--available
as liquid from 5-15% and from on site generators. Less expensive
than chlorine gas. Safer than chlorine gas but is very corrosive
and can decompose rapidly due to heat and sunlight.
b)
Calcium hypochlorite--white dry solid usually containing
65% chorine. Chlorine portion readily soluble but can leave
heavy calcium residues in mixing tanks. Dry material very
susceptible to moisture pick up and cake hardening. Very
corrosive with strong odors requiring careful handling.
Can react with organic matter causing fires.
c)
Chlorine dioxide--Very strong oxidant with relatively
persistent residual. Does not form THMıs nor alter system
pH. Requires on-site generation. ClO3 and ClO2 potential
by-products with possible hydrocarbon odors.
d)
Chlorine gas--Very effective for removing almost all
microbial pathogens and is appropriate as both a primary
and secondary disinfectant. The gas is very dangerous with
lethal concentrations as low as 0.1 per cent air by volume.
Can only be injected in the water supply pipe under highly
pressurized water. Adequate mixing and contact time must
be provided after injection to ensure complete disinfection
of pathogens. May be necessary to adjust pH of the finished
water. All Federal required safety equipment must be observed
in handling. Chlorine gas is supplied in high pressure cylinders.
e)
Chloramine--reaction of chlorine and water with ammonia
whose reaction is 99% complete within a few minutes. Produces
fewer disinfection by-products. Appropriate as secondary
disinfectant preventing distribution bacterial regrowth.
Nitrogen trichloride by-product can result from improper
chlorine to ammonia ratio imparting disagreeable taste and
odor. Chlorine to ammonia ratios of 5:1 should not be exceeded
nor should pH go below 5.0 (or nitrogen trichloride can
form). Can cause occurrence of nitrification. NOTE: Chloramines
in distribution can form methemoglobinemia and can adversely
effect health of kidney patients if chloramines are not
removed prior to dialysis. Same concerns cover pet stores,
fish hobbyists, and aquarium stores. Recommended removal
is by catalytic carbon using a two bed system with a sample
cock in between test for chloramines breakthrough.
f)
Ozonation--Powerful oxidizing agent and disinfecting
agent formed by passing dry air through a system of high
voltage electrodes. Requires shorter contact time and dosage
than chlorine. Widely used as a primary disinfectant. Can
produce halogenated organics if bromide ion is present in
water.
g)
UV Light--generated by a special lamp penetrating organism
cell wall disrupting genetic material making cell unable
to reproduce. Destroys bacteria and viruses. Used as a primary
disinfectant requiring a secondary disinfectant. Does not
inactivate Giardia or Cryptosporidium cysts and should be
used only by groundwater systems not directly influenced
by surface water--where there is virtually no risk of protozoan
cyst contamination.
EPA
recommended control of disinfection byproducts include;
1. Removal
of by-products after formation, which can be difficult and
expensive.
2. Use
alternative disinfectants which do not produce undesirable
by-products.
3. Reduce
the concentration of organics in water before oxidation
or chlorination to minimize formation of by-products.
Aqua
Smart recommends lowering or removing pH control and using
SeaQuest for corrosion and lead/copper control. By lowering
or removing pH control, the more active hypochlorous acid
takes precedence in lieu of the less active hypochlorite
ion increasing distribution residuals allowing for a lower
chlorine input and lower THM and HAA production. Also, by
sequestering metals and coating the metal piping with SeaQuest,
there is less demand on the chlorine making more chlorine
available for disinfection resulting also in higher distribution
levels.
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There are
only three major methods of corrosion control used within the
drinking water industry. These are pH control, phosphate technology,
and sodium silicates. Within phosphate technology, there are many
different types of products available including inorganic (not
organic which are not certified for use in drinking water applications)
orthophosphates and blends, polyphosphates and blends, and ortho/polyphosphate
blends. The corrosion control part of the technology behind all
these phosphates and blends, with one exception, is the formation
of calcium phosphate as a corrosion protective coating. This means
that calcium must be present in the water supply for all these
products to work to whatever degree they do. When calcium is not
present, then it is impossible for the coating to form and no
corrosion control can be provided.
Only one product does not rely on the presence of calcium...that
is SeaQuest. This is because SeaQuest forms a metal phosphate
coating with whatever base metals are present in distribution
piping. This was recently proven in desalination applications
where the produced water is very close to distilled water in quality,
i.e. no calcium present. Lead and copper levels dropped from exceeding
to below the action levels and all discolored water complaints
due to corrosion stopped.
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Inside
this Newsletter 1.
Membrane Technology 2.
New regulations favor... 3.
Disinfection Comparison 4.
On line 5.
Thought of the month 6.
Anyone know the answers? 7.
Chemical feeders 8.
News from over there 9.
All phosphates are the same! 10.
The Bidding Process |
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Thought
of the month
When
Alan Shepard was asked what his first thoughts were on being
the first man in space, he retorted that he could not help
thinking that everything that went into building the spacecraft
he was flying went to the lowest bidder.
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Anyone
know the answers?
1)
What is the energy source which keeps iron bacteria alive?
2) What is the purpose for aeration (i.e. air strippers)?
3) What is the most universal source of taste and odor
problems? |
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There are
many different types of chemical feeders in the marketplace.
Some operate on constant speed with variable stroke, some with
variable stroke and constant speed, and some with variable speed
and variable stroke. Some pumps are flow meter controlled, some
are pace controlled, and others are manually controlled based
on constant flow output. The secret to successfully choosing
the right feed pump besides sizing the pump properly, is to
make sure that the pump will be set up to feed at a very high
speed (input) rate. As such, the best chemical feed pump choices
(regardless of which chemical is being fed) are a constant high
speed pump with variable stroke, a dual control variable speed
and stroke, or a variable speed with a very high speed rate
(300 strokes per minute) at maximum output. In this manner,
the most continuous input is obtainable so that most of the
water going by the injection point gets appropriate treatment.
On smaller systems which require lower feed volumes, it is best
to maximize the chemical feed volume nevertheless to insure
that maximum mixing within distribution takes place. Sometimes
this may require diluting the chemical and even going to a larger
feed pump. By doing this, product performance will be maximized
and the customer gets the best "bang for his buck."
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Off shore in
Europe, a niche market has been established for SeaQuest. This is
treatment of water supplies on cruise ships and military vessels.
All such ships and vessels carry on board storage water supplies
(which they pick up at port) for drinking and general personnel
use. The distribution plumbing on these ships and vessels are the
same as which exists in a municipality with the exception that the
piping is not underground and most corrosion problems are internal.
SeaQuest has been found to be the product of choice here because
of its corrosion control capabilities, stability to time, temperatures,
changes in pH, and wide ranges of water quality in varying port
supplies.
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Inside
this Newsletter 1.
Membrane Technology 2.
New regulations favor... 3.
Disinfection Comparison 4.
On line 5.
Thought of the month 6.
Anyone know the answers? 7.
Chemical feeders 8.
News from over there 9.
All phosphates are the same! 10.
The Bidding Process |
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"All
phosphates are the same!"
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There
is a very strong misconception being maintained by "cheap"
phosphate corrosion control inhibitor manufacturers that the
"cheap" inhibitors are just as good as the more
expensive phosphate corrosion control inhibitors. This is
done by making the statement to potential users that "all
phosphates are the same." The reason this is done is
because a potential customer thinking all phosphates are the
same will inherently believe they can go to bid and then get
the same product from any supplier really believing it is
the same product, but at a lower price.
In reality, just like all cars are different and are manufactured
better and worse or all computers are different and manufactured
better and worse, so to are all phosphate products. Take a
look at the different commercial productsrecently analyzed
for each phosphate component:
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Dry
Products
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Product
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1
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2
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3
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4
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A
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21%
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26%
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1.0%
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52%
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B
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28%
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1.8%
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1.7%
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68.5%
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C
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24.5%
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16%
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1.5%
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58%
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D
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31%
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6%
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44%
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19%
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E
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0.0%
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0.0%
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25%
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75%
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It easily
can be seen from the above that all five dry products are
different with products A and D being extremely different
from products B and C, and from each other while E is altogether
different.
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Liquid
Products
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Product
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1
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2
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3
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A
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30%
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68%
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2%
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B
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40%
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57%
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3%
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C
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50%
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47%
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3%
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D
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10%
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88%
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2%
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Again,
with the liquid products, all formulations are different.
Obviously all the above products will respond in a distribution
system in a different manner and provide different results.
Too, you easily can see that all products will have to be
used at different treatment rates given a constant water quality.
So the big question is who has the best formulation. Aqua
Smart maintains because such formulation variations exists
no products are the same and therefore can never be bid
on an equal performance basis, Product performance backed
by confirming documentation complimented with price per MG
is the only way to validate performance efficacy.
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Anyone
know the answers:
1) Iron bacteria derive energy from oxidation
of ferrous iron to ferric iron. Sequestering the ferrous iron
with SeaQuest (the strongest drinking water iron sequesterant
available) breaks the energy cycle and makes iron bacteria
and biofilms far more susceptible to chorine disinfection
2) Aeration is used to improve taste by removing carbon dioxide,
gases such as hydrogen sulfide, volatile organic contaminants
while also providing enough molecular oxygen to oxidize iron(II)
and manganese(II). Manganese removal by aeration is only feasible
when the pH is raised to 8.5 or higher and provision for contact
with manganese dioxide is made. Raising pH to such high levels
decreases chlorine stability and increases chlorine demand.
3) Geosmin and methylisoborneol (MIB) are two of the most
common taste and odor compounds found in municipal drinking
water supplies. The are thought generally to be metabolites
of blue-green algae and actinomycetes. Other less commonly
found sources of taste and odor in drinking water include
sulfides and saturated and unsaturated aldehydes. Taste and
odor compounds are often detectable by humans at levels of
nanograms per liter.
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Editor's
Note:
We have attempted to provide our readers with topics we believe
to be of interest based on numerous questions and responses
which have been posted on the AWWA Discussion Forum, Water
Technology Forum, and other drinking water forums. We welcome
all responses, recommendations, and suggestions on related
topics you wish to see discussed.
E-Mail
Us with your comments & suggestions |
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Above in 9),
we have established why bidding for corrosion control phosphate
products is risky at best and results in the "cheap" product
winning at worst which often requires higher treatment rates than
specified by the bid and lackluster product performance. Okay, you
say, but what about the fact that the customer is a municipal system
and must go to bid by Council mandate (or if private water by corporate
mandate). That's fine and can be adhered to. But, there are a number
of points which should be introduced into a bid to bring about a
better leveling of the playing field amongst those manufacturers
bidding to avoid being bound necessarily to the "cheap"
product. These include:
1) Ask for a written guarantee that any product usage above that
recommended by the manufacturer based on water quality (assuming
no change in water quality) will be provided free of charge.
2) Test submitted product samples to make sure sulfate and chloride
levels are below 10 ppm. (This should be an internal test and not
made part of the bid specification other than asking for product
samples.)
3) Specify and confirm documentation (customer letters, field data,
test studies, etc.) in support of all product claims.
4) Require and confirm at least 3 references who have used the product
successfully for more than 2 years.
5) Request product comparison studies where available
6) Specify product cost per unit volume of water treated (i.e. $
per MG) in lieu of cost per pound or cost per gallon. This is the
only way to compare true costs assuming the recommended treatment
rates do not require changes related to changes in water quality.
7) Specify and confirm that the product being bid can perform at
a pH level down to 6.0 should the system entertain thoughts of reducing
or getting of pH control.
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Aqua
Smart Inc. 4445
Commerce Drive SW, Suite A4, Atlanta, Georgia 30336 USA
1-800-AQUASMART
Copyright
2001 Aqua Smart Inc.. All Rights Reserved.
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