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The Water
Treatment Process
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Titles to skip to:
Chemical
Process,
Coagulation
Chemistry,
Clarification,
Following Clarification
Filtration
Disinfection
Notice to
Fish Owners and Dialysis Patients
Overview
 The
majority of water
supplied to Project 7
for treatment comes from the Blue
Mesa Reservoir via the Crystal
Reservoir. A small amount
(<5%) comes from Silverjack
Reservoir via Cerro Reservoir.
The water travels down the South
Canal a short distance and a
regulated amount is diverted into
Fairview Reservoir.
Flow through the valve house is
regulated by valves controlled from
the plant. Chlorine is added
to the water to lower the pH, which
allows the aluminum sulfate to work
more effectively. A non-ionic
organic polymer is added to combine
and add weight to the floc
particles.
As
the water passes through the
clarifier, floc particles settle and
the clarified water goes onto the
filters. After the water
passes through the filters, chlorine
is added as a disinfectant and
fluoride is added as a dental health
benefit. During this process,
we reduce the raw water turbidity of
10 to 30 NTUs to around .5 NTU
through the clarifier, and further
reduce it to 0.05 NTU following
filtration. Depending on the flow, a
gallon of water could spend 2 to 6
hours in this process.
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Chemical Process
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The
materials we are attempting to
remove in this process are particles
of varying size and differing
properties. Collectively this
material is referred to as
"turbidity".
Fortunately, algae are not a
significant issue for Project 7 as
it can be in some operations. We do,
however, have the task of removing
finely divided particles. Some
of these particles, if allowed,
would take years to "settle out".
They are referred to as "colloidal".
Therefore, we assist the settling
process by the addition of aluminum
sulfate to destabilize the
electrical charge of the particles.
This process allows for the
formation of a settleable material
called "floc". Additionally,
we add an organic polymer to further
enhance the settling process.
The initial destabilization of
particles and the formation of a
micro floc take only a few seconds.
Within a few minutes the floc
particles begin to grow, resembling
brown snowflakes. Eventually, the
floc particles become denser than
the water supporting them and begin
to settle, entrapping the materials
we are attempting to remove and
become sludge.
Coagulation Chemistry
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RAW
WATER PARTICLES ARE MOSTLY
NEGATIVELY CHARGED. THEY TEND TO
REPEL ONE ANOTHER, AND STAY IN
SUSPENSION.
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15-30 PPM DOSE OF ALUMINUM
SULFATE CONVERTS ABOUT HALF OF
THE NEG (-) PARTICLES TO
POSITIVE (+).
-
THE
OPPOSITELY CHARGED PARTICLES (+
& -) NOW ATTRACT ONE ANOTHER AND
FORM LARGER, HEAVIER CLUMPS OF
PARTICLES CALLED FLOC. A
NON-IONIC POLYMER IS ADDED TO
CHAIN THE FLOC PARTICLES
TOGETHER.
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FLOC SETTLES TO THE BOTTOM WHEN
SUFFICIENTLY HEAVY, LEAVING
CLEARER OR "CLARIFIED" WATER ON
TOP.
The settled particles, now called
sludge, are released out to the
drying beds for removal.
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What Happens
After Chemicals are Added?
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The
chemically treated water enters the
clarifier in the center where it
comes in contact with gentle floc
mixers and a floc blanket.
During its travels through the
clarifier, the water deposits its
particles through contact with other
floc particles. The floc
particles continue to cling to one
another until they become large
enough to settle and become sludge.
Tube settlers are positioned just
below the effluent collection weir
and are angled to provide a
hydraulic loading against the
particles. The clarified water
spills into the effluent weirs,
around the outer ring, and is then
piped to the filters.
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Following Clarification
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The
water from the clarifier flows onto
the top of the filters where it
passes through the various media.
The anthracite, (or crushed coal)
does most of the work capturing the
majority of particles. When a filter
is first started, a mat is formed by
the particles. This mat is
called a schmutzdecke (pronounced
shmoots-deck). The
schmutzdecke helps capture more and
more of the particles until the
anthracite becomes so thick with
particles that the filter will
eventually require "backwashing" or
cleaning. During the backwash,
water is pumped at a high rate up
through the filter to expand the
filter media and allow the built up
particles to escape and drain into
our reclaim pond. The sludge from
the backwash settles and the
decanted water is returned to the
raw water line for recycling.
Following the
clarification process, fluoride is
added to the water. The
concentration of fluoride is
monitored and adjusted to maintain
approximately 1.0 milligram per
liter. This is the concentration
suggested by the Colorado Department
of Public Health and the American
Dental Association.
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Disinfection
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The last step in our treatment
process is disinfection. Chorine is
added as our primary disinfectant.
This is the last barrier against any
pathogens that may have survived the
treatment process. To improve the
taste, odor of our water, and to
ensure a residual disinfectant in
the outer limits of the distribution
system we use chloramines as a
secondary disinfectant. The “free”
chlorine in the water is converted
to chloramines by adding a trace
amount of ammonia, forming
chloramines.
Fish owners and kidney dialysis
patients should be aware:
It should be noted that chloramines
are toxic to fish. Unlike chlorine,
chloramines cannot be removed by
allowing the water sit out
overnight. The chloramines can be
removed by additives, which can be
found in local pet stores.
People who use home dialysis
machines must also remove the
chloramines. Contact your health
care provider for more information.
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