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Water Treatment Water Quality



Water Quality Parameters

 

Hardness can be converted from mg/L to grains per gallon by dividing mg/L by 17.1.

So 150 mg/L hardness shown above is equal to 8.8 grains per gallon hardness.


In addition to the general water quality parameters listed in the table above, the City publishes an annual Water Quality Report (Consumer Confidence Report), listing the maximum observed value for several regulated contaminants as well as information on the sources of our water, the treatment process, water conservation tips, etc. You can also request a copy of this report by calling the Water Treatment Plant at (405) 321-2182.


In operating the plant, we conduct numerous tests on the water we produce, both for control of the plant and for reporting to the Oklahoma Department of Environmental Quality. We run a series of tests every two hours, including alkalinity, pH, hardness, fluoride residual, chlorine residual, and turbidity on the incoming water, the finished water, and at several steps throughout the treatment process. We perform other tests twice per day, such as chlorides, water temperature, and stability. Every day we test water from the distribution system for fluoride and chlorine residuals. We test 90 samples per month for bacterial contamination. In addition to the tests we perform the Oklahoma Department of Environmental Quality tests samples on a regular basis for other parameters we cannot test here. These include heavy metals (such as lead, copper, arsenic, etc.), volatile or synthetic organic chemicals, and disinfection by-products. We go to every effort to ensure that the water we produce is safe and available 24 hours per day, 7 days a week.










     Alum vs Ferric       

HISTORY:

The
Norman Water Treatment Plant is a lime softening plant and has been using
Aluminum Sulfate (Alum) for their coagulation process since 1966.  Norman softens the water from approximately
180 mg/l to 120 mg/l total hardness.  The
treatment system utilizes Solids Contact Clarifiers and feeds straight to
filters without a sedimentation basin. 
Ferric sulfate (Ferric) was trialed in the 1990’s and showed great
results but at the time was twice the cost of Alum.  Also several polymers have been trialed at
the water treatment plant and have had adequate results but heavily depended on
seasonal changes which caused large temperature swings.  Additionally, since the treatment train does
not have intermediate settling basins, the polymers were too slow to react and
would sometimes coagulate in the water on top of the filters causing blockage
of flows.  This study reinvestigated the
comparison of Alum versus Ferric as a treatment coagulant for the Norman water
treatment plant and yielded promising results.


COSTS:

Ferric
Sulfate requires a much higher pH to perform properly than alum.  The higher pH requires a higher lime feed
rate, and also requires more CO2 following the softening reaction to reduce the
pH to proper levels for the tap.  This
increases both lime and CO2 costs. 
However, ferric sulfate requires a much lower dosage to work, and is
somewhat cheaper per pound than alum. 
The result is a net savings in chemical costs.  The bottom line is that our average cost for
coagulant, lime and carbon dioxide is about $136.92 per million gallons when
using alum, and about $127.84 per million gallons when using ferric
sulfate.  Costs for the other chemicals
(chlorine, ammonia, activated carbon and fluoride) will be the same for either
coagulant.


The
savings of $9.08 per million gallons should translate to an annual total
savings of approximately $28,000 based on our total allocation from Lake
Thunderbird.


PERFORMANCE:

Average
tap turbidity for ferric sulfate was 0.086 NTU versus 0.097 NTU for alum.  The difference is probably not significant.


We
have tested for iron in the tap and seen no significant increase due to the
ferric sulfate.  We believe we had a
problem several years ago when we first tried ferric sulfate.  Since then we learned that ferrous sulfate
tends to carry through the treatment process and show up as tap iron.  We specified a ferric sulfate with a low
ferrous content and believe this has solved the carry-through problem.


When
using alum, the two small clarifiers were fairly easy to upset and required
fairly close observation.  The large
clarifiers were much more stable in treatment and could survive larger
excursions of operation without major changes in water quality.  Using ferric sulfate, the operators report
that the behavior has switched.  The large
clarifiers are more prone to upset, and the small clarifiers are more stable.  Staff will continue to investigate this
phenomenon. 


Another
performance difference is that carbon dioxide has become much more critical
with ferric versus alum.  When operating
with alum, we frequently only increased the pH slightly with lime, and had to
feed very little carbon dioxide to lower the pH back to desired levels.  This meant that a failure of the carbon
dioxide feed had only slight effects. 
Using ferric sulfate, we are always making significant changes in pH
with the carbon dioxide.  Failure of the
carbon dioxide feed results in a significant increase in filter turbidity and
reduction in filter run times fairly rapidly. 
We can only operate without carbon dioxide feed for a very short time
(several hours) without significant impact. 
We have some redundancy built into the system, but will continue to monitor for summer peak flows.


SLUDGE PRODUCTION:

We
do not have an estimate of the difference in sludge production.  The increased softening will probably
outweigh the lower coagulant dosage, and we believe we are producing more
sludge with ferric sulfate than with alum. 
We have not hauled a lagoon with ferric sulfate / lime sludge yet, but
from the literature we expect it to dry more easily and be easier to
handle.  We cannot evaluate sludge
handling costs at this time.


Ferric
sulfate sludge should be more amenable to land application than alum sludge.  Farmers are not as accepting of sludge with
aluminum content but are fine with iron content.  So it might offer more options when we have
to find an alternate sludge disposal method.


CORROSION:

It
is reported that ferric sulfate (and ferric chloride even more) is corrosive
and can shorten the life of clarifier mechanisms.  We took pictures before we started using
ferric sulfate to attempt to evaluate this claim but don’t have any “after”
photos for comparison.  We need to
monitor our clarifier mechanisms and if we see any problems arise, we may need
to look at repainting more often, or installing other corrosion control
alternatives.


CONCLUSION:

We
see no serious problems associated with using ferric sulfate, and see several
advantages.  We expected the staining
from the iron to cause house-keeping problems, but have not seen any serious
problems so far.  We will continue to monitor corrosion on the steel clarifier equipment, and may need to increase our
frequency of repainting, but we believe ferric sulfate is a very good option to
alum as our primary coagulant.








While on alum (July, 2013 through October, 2013) we saw the following


average performance:






Alum

362

Pounds
per million gallons



Lime

1026

Pounds
per million gallons



CO2

323

Pounds
per day




Flow

11.1

MGD





CO2

29.0

#/MG





Tap
Turbidity

0.097

NTU














The complete switch to ferric sulfate began in November, 2013.  From November,

2013 to July, 2014 we saw the
following average performance:



Ferric
Sulfate

214

Pounds
per million gallons



Lime

1213

Pounds
per million gallons



CO2

300

Pounds
per day




Flow

8.4

MGD





CO2

35.7

#/MG





Tap
Turbidity

0.086

NTU













Alum

Ferric

Lime

CO2


Costs per lb

0.145

0.130835

0.0805

0.062








Cost per MG







Alum

Ferric




Coagulant

 $   52.51

 $   27.98




Lime

 $   82.61

 $   97.65




CO2

 $    1.80

 $    2.21




Total

 $  136.92

 $ 127.84










Savings:

 $    9.08

per
million gallons









Production

3082                                                

MG/year
(if we just use our allocation)







Annual savings

 $27,995.18