CASE
STUDY:
Coon Rapids, Minnesota
City Expands Existing Electromedia® System for Iron and
Manganese Removal
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City Expands
Water Treatment Facilities to Meet Growth.
Background
The City of Coon Rapids,
Minnesota recently completed the expansion and upgrade of its East and
West Water Treatment facilities. Production at the plants was increased
by 66% at the East Plant and 40% at the West Plant to bring the total
design capacity to 22.3 million gallons per day. New filters, additional
backwash water reclaim capacity, chemical feed systems,  and
new control systems for plant operations and telemetry were included
in the projects.
Like many municipalities, the City of Coon Rapids faced a variety of
decisions in planning for the treatment of iron and manganese found
in the majority of their wells. A comprehensive water system study favored
the use of common, centrally located plants versus multiple satellite
plants. Choosing the treatment method involved an extensive review including
site visits for different filtration technologies. City personnel and
their consulting engineers traveled to California to visit several Filtronics
installations and their manufacturing facilities.
Plant Expansion
Ultimately, the City of
Coon Rapids chose Filtronics Electromedia®
I filtration technology for their East and West Treatment plants.
The facilities with capacities of 4000 and 7000 gpm, respectively, were
installed in 1991. After 15 years of service, each plant was expanded
to 6000 and 10,500 gpm, respectively. The original design left space
on each of the sites to allow for the physical expansion.
Two new Filtronics’
Electromedia® I filters for iron and manganese were installed
at each facility to add to the existing Electromedia filters put into
service in 1991. Each of the filters is designed to run at 10 gallons
per minute per square foot.
The reclaim systems were
expanded in capacity to allow for the additional backwash volume created
by the new filters. Water from the four minute backwash and one minute
purge (filter to waste) cycles of each filter is sent to the reclaim
tanks. After a settling period, where the iron and manganese treatment
residuals settle out, the supernatant is blended with the well water
at the headworks of the treatment plant.
More than ninety nine percent
of the water used for backwash and purge is recycled. At design capacity
this means that more than 200,000 gallons per day of water can be recovered.
Automated Controls
The chemical feed systems
are completely automatic. New automatic rate valves for chlorine and
sulfur dioxide gas were installed. Upgrades to the chemical systems
were performed by Larsco, Incorporated of Anoka, MN.
The original plant control systems used painted graphic panels with
small lights for plant process indications. Each of the systems was
upgraded with large graphic display panels, new programmable logic controllers
(PLC’s), and new telemetry control. The system now runs on an
ethernet network with a virtual private network (VPN) set up. The VPN
allows the operators to remotely access the telemetry and plant operating
systems with a laptop and an internet connection.
The combination of these
upgrades allows each facility to be run by one operator. Each operator
has plenty of time for regular maintenance at the plants which also
house distribution system booster pumps.
Conclusion
Iron and manganese in the
raw water is as high as 1.0 mg/L. The treated water from both facilities
is usually less than 0.020 mg/L with many non-detectable results.
The upgrade of these treatment
facilities provides the 65,000 residents of the City of Coon Rapids
with treated water from fifteen different wells with expandability to
meet future needs of the water system. The two projects with a total
value of $5.7 million dollars were designed by TKDA of Saint Paul, Minnesota
and constructed by Municipal Builders Incorporated of Andover, Minnesota.
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