WASTEWATER TREATMENT FACILITY
The
current facility was constructed in 1986, and upgraded in 1998
to provide biological phosphorous removal, and in 1999 to construct
auto-thermal aerobic digesters, and revise the preliminary treatment
building. The upgrade was completed in January 2000. The facility
is designed to clean 1.8 million gallons of wastewater per day,
and remove 5,300 lb. of BOD(Biochemical Oxygen Demand) per day,
6,997 lb. of suspended solids per day, and 99 lb. of phosphorus.
per day.
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The
wastewater entering the treatment facility is a grayish
brown mixture of the original clean water, and all the pollutants
picked up from various sources. The wastewater has a slightly
musty, stale odor, which is not strong or overpowering.
This picture shows a sample of the wastewater entering the
facility.
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Wastewater flows through
the 36-inch interceptor sewer to the Facility. Septage haulers
discharge septage into a manhole located about 500 ft. upstream
of the preliminary treatment building. Septage is mixed with
the incoming wastewater and carried into the facility. Leachate
from the Portage County Landfill is accepted at the Facility in
a 15,000 gallons receiving tank. The tank has a mixer and two
grinder pumps to pump the leachate into the 36-inch sewer about
50 feet upstream of the preliminary treatment building.
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The
first step of the cleaning process takes place when the wastewater
enters the preliminary treatment building and flows through
a fine screen. The fine screen removes all the large debris
from the wastewater stream. The screenings are cleaned, compacted,
and placed in a dumpster, and disposed at the landfill. |
The wastewater flows through a grit removal system. Sand and
other heavy inorganic materials are removed, cleaned, drained,
and deposited in a dumpster. The wastewater then flows through
a 12 inch parshall flume with an ultrasonic measuring device
for flow measurement. The wastewater falls into a wet well
and is pumped to the oxidation ditch by a combination of five
submersible influent pumps. A composite sampler collects samples
of the influent. |
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The
heart of the treatment facility is the oxidation ditch. The
organic and suspended materials are removed from the water
by a process as simple as nature itself. Bacteria common
to and river, lake, or pond, are the tools that clean up the
water. The treatment facility is essentially a large reactor
designed to maintain the proper conditions for the bacteria
to live and work. |
| The bacteria
use organic material as a food source. The oxidation ditch
provides oxygen to keep then alive, and continually mixes
the bacterial and the wastewater so the bacteria can find
and absorb the food they need. Nutrients, such as phosphorus
and nitrogen, are also removed when proper conditions are
present in the process. |
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This whole process is completed
in a matter of hours. At the end of the process, the organic and
suspended matter has become part of the bacteria cells. The next
step is to separate the bacteria and the water. Separation occurs
in the clarifiers.
The oxidation ditch consists
of three nearly circular concentric channels. The wastewater
enters the outside channel, or channel no. 1 of the oxidation
ditch. Channel no. 1 has four disc aerator shafts at 90-degree
intervals around the nearly circular ditch. A 40 hp motor drives
each aerator. Return activated sludge is pumped from the clarifiers
to channel no. 1 and enters 180 degrees from the wastewater. Wastewater
and return activated sludge (RAS) are mixed and aerated. The
mixture moves to channel no. 2 and channel no. 3 through submerged
ports. Two disc aeration shafts provide aeration in channels
no. 2 & 3. Each shaft extends across both channels. Each
shaft is driven by a 75 hp. Motor with a variable frequency drive.
The mixture exits the oxidation ditch through a submerged port,
over weirs, and through underground piping to either of two clarifiers.
The volume of the oxidation ditch is 2.954 million gallons.
Conditions in oxidation
ditch are controlled by a sophisticated computerized monitoring
and control system to provide the proper environment for biological
phosphorus removal to take place. A chemical feed system was
constructed during the upgrade, to provide chemical phosphorus
removal capability as a backup to the biological system.
Clarifiers are large tanks
that provide quiescent conditions. The bacteria are slightly
heavier than water, and will settle to the bottom, given enough
time and quiet conditions. A concentrated bacteria/water mixture
is pump from the bottom of the clarifiers, and returned to the
oxidation ditch, and the cycle starts all over again.
Cleaned water
from both clarifiers is mixed in the effluent
collection well. Samples of the effluent are taken from this
well by 24 hour composite sampler. Water flows from the collection
well to the disinfection system.
The disinfection system
is operated from May 1 to September 30. During this period the
water enters a mix chamber where a chlorine solution from the
gas chlorination system is discharged through a submerged injector.
A propeller mixer in the chamber mixes the effluent and the chlorine
solution. The chlorinated effluent flows through the chlorine
contact tank. Sulfur dioxide solution from the gas sulfur dioxide
system is discharged through a submerged tank header about six
feet from the end of the contact tank. De-chlorinated effluent
flows over a weir at the end of the contact tank about 1200 feet
through underground piping to the river outfall. Treated effluent
is discharged to the Wisconsin river.
The process provides optimum
growth conditions for the bacteria, and there is an ample food
source in the wastewater. The bacteria grow and reproduce in
the system. The most efficient removal is obtained at a certain
balance between the bacteria in the system and the amount of food
entering the process. As the bacteria grow and reproduce, a
portion of the bacteria must be removed on a regular basis.
Excess bacterial solids or “biosolids” generated by the process
are diverted from the RAS piping into an aerated storage tank.
The biosolids from the storage tank is fed to a gravity belt thickener
where 94 to 96% of the water is removed. Thickened biosolids
is discharged into the auto-thermal aerobic digesters.
The biosolids entering the
digesters is quite active, viable, and have a high proportion
of organic material incorporated into its cell mass. The biosolids
in this state are unstable and could create strong odors, attract
flies, and be generally undesirable. The biosolids are treated
further to reduce their organic content in digesters. The digesters
stabilize the biosolids by blowing air through the mixture, and
raising the temperature to about 110 degrees F. The biosolids
are held under these conditions for 40 to 80 days. At eh end
of this process, the biosolids have a relatively low organic content
and will not cause odors, attract flies, and etc.
These digesters consist
of three tanks; each having floor mounted fine bubble aeration
diffusers and a propeller mixer. The blowers, pictured here pump
air through the mixture. Biosolids flow through the digesters
in a plug flow mode. Biosolids exit the auto-thermal digesters
and flows to a pre-existing aerobic digester.
Digested biosolids are pumped
to the belt press. This machine drains and squeezes additional
water from the biosolids. Polymer and ferric chloride is injected
into the biosolids to help release additional water. The biosolids
is discharged in cake form at about 16% solids content. The cake
solids is moved to a covered storage pad and stored until the
biosolids are applied to agricultural land in spring and fall.
While the biosolids are
organically stable, they do generous amounts of nitrogen and phosphorus.
These, of course, are two of the main constituents of commercial
fertilizer. The treated biosolids are applied to agricultural
land, and serve as a fertilizer and soil conditioner. The high
amounts of organic matter in the biosolids are especially attractive
in areas with sandy soils, to help build the soil organic levels.
Samples of the wastewater
coming into and leaving the treatment facility are taken and tested
daily. The data is used to monitor the amount of pollutants coming
into the treatment facility, the conditions and performance of
the processes, and the quality of the water leaving the facility.
Some of this data is reported monthly to DNR to verify compliance
with requirements. The rest is used in the day to day operation
of the facility.
The Wastewater Utility operates
24 hours per day, 365 days per year. Wastewater never takes a
holiday.
The
staff of 4 is responsible for operation, maintenance, lab work,
record keeping, and administration, as well as, operation and
maintenance of the collection system, industrial monitoring, working
with new industrial dischargers, meeting regulatory requirements,
answering alarms, marking locate requests, monitoring construction,
and other associated duties.
Cleaning the water the Village
uses is a major undertaking, not only in the effort, but also
the cost. As higher and higher levels of clean water are demanded,
the efforts and cost will increase. The Plover Wastewater Utility
is well situated to meet those demands.
If you want more information
on the Plover Wastewater Utility, please call the Manager at 715
345-5259. Tours are available, but arrangements must be made
in advance.
