Plant History |
The original plant became operational in 1953
and many of the treatment units remain in use today.
The first treatment equipment consisted of a pump station,
flow meters, four clarifiers to physically remove solid materials from the
waste stream, and two sludge pumps. Two
Anaerobic digesters (Primary and Secondary) were used to biologically
reduce the organics in the solids that are removed as part of the
treatment process. Sludge
drying beds were used to dewater and dry treatment residuals.
The final treatment process involved the addition of chlorine gas
to kill pathogenic organisms before the treated wastewater was discharged
to the Thunder Bay River. The
plant removed about 15 to 20% of the pollutants that entered the facility.
In 1972, the plant was upgraded to improve pollutant removal capability. Using grant funds from the USEPA, secondary treatment was added to
the facility. A biological
treatment process called Activated Sludge was used to enhance removal of
dissolved pollutants from the wastewater. This addition improved pollutant removal rates and the plant
regularly achieves 90 to 95% pollutant removal efficiency.
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Preliminary
Treatment |
This part of the plant
accomplishes the removal of screenings and grit from the raw wastewater. A
screen positioned perpendicular to the flow captures rags, plastics,
sticks, and debris that could plug up pumps and sludge collectors. A
cutting bar moves across the screen and chops up the collected material
into small pieces that will not clog downstream treatment equipment. This
debris cutter is called the comminutor.
A grit channel is the next treatment process. The sewer system is
designed to provide a minimum internal flow velocity of 2 ft/sec. The grit
channel is designed to reduce that velocity to 1 ft/sec allowing heavy
debris like sand, gravel, and other abrasive material to settle to the
bottom of the channel. If left in the wastewater flow, this material would
abrade pump impellers, collectors, and other mechanical equipment. The
removed grit is collected, stored, and disposed of by land filling.
Comminutor
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Primary
Clarifiers |
The raw pump
station lifts the wastewater into four rectangular tanks that have a
capacity of 100,000 gallons each. The
velocity of the wastewater is slowed to 0.5 ft/sec, which allows solids
that are heavier than water to settle to the bottom of the tank,
clarifying the wastewater. This
part of the treatment process became operational in 1953, and
accomplishes about 15 to 20% pollutant removal. 
Primary Clarifiers
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Aeration
Reactors |
The settled
sewage pump station lifts the primary effluent up into two 600,000-gallon
aeration reactors where it is mixed with activated sludge bacteria. A centrifugal blower compresses and moves air to the bottom of the
reactor supplying the bacteria with dissolved oxygen necessary for
respiration, and mixing the tanks contents. At normal flows, it takes a gallon of wastewater from 7 to 10 hours
to pass through the reactor. The
bacteria remove the pollutants from the wastewater and use them as an
energy source. These tanks
went into service in 1972, and where covered with aluminum hatches to
control inherent odors that are generated by the process. 
Aeration Tanks
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Final
Clarifiers |
The
discharge from the aeration reactors is directed to the center of two
500,000–gallon final clarifiers. In
the absence of agitation, the bacteria settle to the bottom of these
circular tanks. The center of
the clarifier supports and drives two rake arms that move the settled
solids into a sludge box in the center of the tank. Pumps collect and move the settled bacteria mixture back to the
head of the aeration reactors. The
purified water moves to the outside of the tank, and flows over the
discharge weirs.
Final Clarifiers
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Biosolids
Application Program |
Biosolids are semisolid and liquid residues
generated during the biological treatment of the wastewater at the water
recycling plant. This
nutrient-rich material is recycled to beneficially enrich soils. Area Farmers are the main benefactors of this program, which
helps them reduce their costs for commercial fertilizers. Biosolids are also used to regenerate forest growth and to reclaim
areas destroyed during industrial mining operations.
Approximately 3
million gallons of biosolids are applied annually to improved soil
structure and fertility. During
the spring and summer growing season the liquid biosolids are transported
to the application site with a 6,000-gallon tanker truck. During winter months when application is suspended, the material is
stored in a 1-million gallon above ground storage tank.
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Mercury
Minimization |
Mercury is a naturally occurring element
that is recognized as a bioaccumulative chemical of concern. When mercury enters the environment it tends to
concentrate in organisms that are at the top of the food chain. Over the last 15 to 20 years, game fish consumption
advisories have been issued in Michigan because of elevated mercury levels
in the fish. The Alpena Water
Recycling Plant first implemented a mercury minimization in 1986. The focus of the plan was to identify and eliminate mercury
discharges from commercial and industrial sources. Utility personnel have assisted in the identification of
numerous over-the-counter products that utilize mercury as a preservative. Once identified, mercury free products can be substituted.
For
example, Alpena General Hospital sponsored a mercury thermometer exchange
program that provided participants with a digital thermometer as a
substitute.
Further progress in reducing mercury in wastewater discharges must be accomplished by educating the general public about the mercury pollution
prevention. Many products that are purchased
over-the-counter can contribute mercury to the environment, without the
user even knowing. Information about mercury minimization can be
found at the Michigan Department of Environmental Quality Web Page http://www.michigan.gov/deq/0,1607,7-135-3585-11756--,00.html
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Industrial
Pretreatment Program |
The water
recycling plant management staff regulates Commercial and Industrial
wastewater discharges. Chemicals
that could upset the biological processes at the plant must be strictly
controlled. The indiscriminate discharge of metals and other toxins can
also pass through the plant and enter the environment. Customers that have the potential to negatively impact plant
processes are issued discharge permits and are inspected annually to
insure compliance with limitations.
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Pathogen
Reduction |
Chlorine bleach is added to the treated wastewater after
secondary treatment is complete. Chlorine
is a strong oxidizer that kills organisms that could cause diseases. The toxic qualities that make chlorine a good disinfectant would have
a detrimental impact on the environmental if it were discharged directly to
the river. Therefore, the
chlorine must be neutralized with Sodium Bisulfate before the treated water
is released to the environment.
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Odor
Control |
The equipment and infrastructure necessary to transport and
recycle wastewater creates conditions that are inherently prone to the
creation of odors. The
offensive odors are typically caused by the bacterial decomposition of
organic compounds. The classic
rotten egg sewer gas odor is one byproduct of this process. Because of the plants close proximity to the boat harbor area. The Alpena Municipal Council voted to add 1.5 million dollars
worth of odor control equipment to the facility. All treatment vessels have been covered to contain inherent
odors. The foul air is moved by
a series of fans, blowers and ductwork to two odor scrubbers. These scrubbers use bleach and caustic soda to chemically remove the
odor causing agents found in the collected air.
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Anaerobic
Digesters |
Any wastewater treatment process generates
solids that must to stabilized and recycled. Two 300,000-gallon anaerobic digesters are used to treat the solid
material generated by the Alpena Water Recycling Plant. The digesters are similar to a septic tank, except modifications are
made to the process to speed up the bacterial activity. The primary digester is heated to between 90 and 100 degrees F and the
contents of the tank are mixed using compressed digester gas.
A valuable byproduct of
the anaerobic digestion process is methane gas. This energy source is used to fire the plant boiler and fuel a
4-cyclider engine that drives a raw wastewater pump. Utilization of methane gas from the digester saves the
Utility about $15,000 in energy costs.
Anaerobic Digesters
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