Energy- and
Labor-Saving Solutions
By Joe Zwers
he Stevens Point Wastewater Treatment Plant (WWTP) in
Stevens Point, Wis., is located in a university town of 25,000
residents. It keeps the local environment clean by treating an average of 3
Award-winning Wisconsin WWTP
adopts green filters
million gal of sewage a day before releasing the water into the Wisconsin
River. In 2007, the plant received a “Laboratory of the Year” award from
the Wisconsin Department of Natural Resources (DNR). As DNR Audit
Chemist Camille Johnson stated, not only were no deficiencies found in
an evaluation of the lab, but the operators “are very dedicated and make
changes when they learn that there is a better way of doing something.”
The Stevens Point WWTP treats an average of 3 million gal of sewage a day.
That willingness to adopt new
procedures extends to the rest of the
facility. The last decade has seen
the adoption of a series of actions to
improve efficiency and reduce energy
usage. This includes the utilization of Tekleen MTF-1 (1-in. NPT,
100-gal-per-minute [gpm]) filters with
200-micron wedge-wire screens on the
wastewater they use to provide heat
and cooling for the plant buildings.
“These self-cleaning filters are an
energy-efficient, green type of filter,”
said Eric Niffenegger, plant superintendent. “Instead of using a lot of electricity, they harness the energy from
the flow of water going through them
to power the cleaning cycle.”
The past decade has seen the adoption of a series of new technologies to improve efficiency and
reduce energy usage at Stevens Point.
70 Years of Improvements
The Stevens Point WWTP dates
back to the Great Depression. The
city had been dumping its raw sewage into the Wisconsin River, but the
state ordered it to begin primary treatment. Rather than complying with the
minimum requirements, the city built
a secondary treatment facility in 1940.
Later upgrades in the 1960s and 1970s
included a switch from mechanical aerators to a compressed air system, and
the addition of three sludge lagoons,
two primary settling tanks and two
aeration tanks.
The WWTP was rebuilt in the 1990s
to take advantage of newer technologies, including mechanically cleaned bar
screens, ultraviolet (UV) disinfection
instead of chlorine, and biological phosphorus removal. A grit removal system
was added to reduce pump wear, and
the sludge storage lagoons were replaced
with sludge storage tanks.
Starting in 2003, more emphasis
was placed on improving plant efficiency. This led to the installation of
grit removal and fine screening equipment, a single 15-hp air compressor
replacing two 50-hp compressors, and a
108-bulb self-cleaning system replacing
a 672-bulb UV disinfection system.
The efficiency gains extended
beyond the water treatment process
itself. Heat pumps have been installed
in two main buildings that use the
treated effluent water for heating and
cooling. Although both buildings also
have forced air gas heaters, they are
only used as a backup.
In February, temperatures drop
below 0°F at night and highs are about
20°F. “The wastewater is warmer than
the groundwater, so it is a good place to
extract heat in the winter,” Niffenegger
said. “On the buildings where we have
the heat pumps, we are not using any
natural gas currently.”
Lightening the Labor Load
An integral part of the plant’s strategy for using effluent water is to incorporate more efficient filters as part of
the water treatment program. Tekleen
filters incorporate self-cleaning systems
that use less water for the rinsing of the
screen than traditional backflushing
systems. Tekleen’s MTF (Minitwist)
Series are low/medium-flow-rate filters,
fully automatic, self-cleaning water filtration systems. These filters can handle flow rates from 1 to 2,400 gpm
with screens as small as 10 microns.
The MTF filters use very little water
for the cleaning of the screen. They are
january 2011 • Water & Wastes Digest
After seeing how well the first application of new filters went, the plant began considering other
applications for the technology.
rated to 150 psi and 210°F. The filters
are all made from stainless steel material and designed to satisfy a wide variety of industrial and irrigation application requirements.
During filtration, solids build up on
the inside of the fine screen, creating a
pressure drop at the filter outlet. When
a 7-psi differential between the inlet
and outlet to the filter is established,
the filter controller is triggered to open
the flushing valve that will initiate the
4-seconds-long suction of the screen
with the use of only 4 gal of water
without interrupting the main flow.
Opening the flush valve creates an
atmospheric pressure path inside the
cleaning mechanism, and the nozzles
vacuum the dirt from the inside surface
of the screen. A hydraulic motor causes
the scanner to rotate in order to cover
the entire screen surface in 4 seconds.
At that point, the flush valve closes
and the cleaning mechanism returns
to its starting position. Other than a
low control voltage for the differential
pressure sensor and actuation of the
flushing valve, all motions involved in
cleaning the filter are performed using
water pressure.
The WWTP selected it first Tekleen
product to replace the main filter for
all the nonpotable water supplying the
seal filters, the fire hydrants and the
lawn sprinkling system. The old filter
clogged easily and frequently would
break down. It became a daily duty to
take out the strainers, clean them off
and put them back in.
“Even if the cleaning went
smoothly each time, just by virtue of
having to take the filters out and
manually clean them off, you are
wearing parts out and they are prone
to break,” Niffenegger said. “With
some of the manual strainers, the
housing would actually crack from
opening and closing them so much.”
The replacements did not experience
those problems due to their self-cleaning
mechanism. Installing one on the main
nonpotable water line eliminated regular
manual cleaning and breakages.
“After seeing how well it worked
compared to that original strainer,
we started thinking about other
applications for Tekleen filters,”
Niffenegger said.
The Stevens Point WWTP deployed
another filter on the fine-screen rag
auger cleaning operation, where nonpotable water is used to wash the rags off
before they go into a dumpster. A third
filter went on the heat pump in the
office/laboratory building. When the
plant added a building to house equipment and offices for the collection system, a self-cleaning filter went on the
facility’s heat pump.
“In addition to energy savings, we
have regained at least a man per day
per week by switching to the new filters,” Niffenegger said. “[The] filters
freed up our staff for other important
tasks instead of spending their time
cleaning out the filters.” WWD
Repair &
This water treatment plant at the City of
Carrollton in Georgia was in need of repair. After
a careful evaluation of possible repair strategies,
Xypex Megamix II was chosen for its excellent
structural resurfacing and waterproofing properties
to restore the interior of the basins, influent channels
and flocculators. The exterior wall elevations,
horizontal walkways and beams were coated with
Xypex Crystalline Waterproofing prior to application
of finishes.
Joe Zwers is a writer specializing in
business and technology. For more
information, contact Daniel Flanick at
dsf03@aol.com or 800.336.1942.
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