The City of Watertown wastewater treatment plant was designed by
Brookﬁeld, Wisconsin ● (262) 784-7690 ● www.ati-ae.com
• The treatment plant construction
was bid in 2002 for a cost of $23.6
• Major interceptor work associated
separately for a cost of $3.6 million,
including a new 5-foot diameter
interceptor on Hoffmann Drive
and a 4-foot diameter interceptor
crossing the Rock River.
• The construction was ﬁnanced
by a low interest loan from the
Wisconsin Clean Water Fund.
• The treatment plant can treat 5.2
million gallons on an average day,
up to 24 million gallons on a peak
• Annually, the plant can treat and
return enough highly treated water
to the Rock River to ﬁll a 500-acre
lake to a depth of almost 12 feet.
• The combined holding capacity of
all of the tanks totals 5.6 million
gallons, which is equivalent to a
football ﬁeld ﬁlled to a depth of 13
• The City is underlain by 105 miles
of sewers collecting wastewater
from an area of 12 square miles; the
collection system includes 19 lift
• The treatment plant is equipped
with its own emergency power
generator to keep the plant running
in the event of a power failure; the 2
MW generator can provide enough
energy to power up to 100 homes.
(1) Wastewater entering the plant is
collected in the Raw Sewage Pump
for screening to remove coarse debris.
(3) The screened wastewater ﬂows to grit
chambers to remove heavy particulate
matter like sand and gravel.
(4) Primary clariﬁcation is next, where
the wastewater undergoes gravity
settling to remove solid pollutants;
is completed after this stage.
(5) The wastewater then ﬂows to the
aeration basins, where a mixture of
(6) Final clariﬁers remove the microbes,
leaving highly treated water cleansed
of more than 99% of the pollutants.
(7) The water is disinfected with
ultraviolet light to kill bacteria and
just prior to release into the Rock
(9) Residual materials from the treatment
stabilization through fermentation in
(10) The digested residuals are further
reduced through dewatering
prior to being used as an agricultural
(12) Plant administrative, operations and
laboratory facilities are housed in the
(13) Plant maintenance functions are
housed in the Maintenance Building.
Wastewater Treatment Process
Do you have questions about the City of Watertown
wastewater treatment plant? Would you like a plant
tour? Please contact us at (920) 262-4085.
Wastewater Treatment Plant
What is wastewater and why is it treated?
Every time you use water to take a shower, wash the dishes,
do the laundry, or ﬂush the toilet, the used water becomes
dirty wastewater that drains away via the sewer system.
Wastewater from homes, businesses, and industries
contains pollutants that can harm the environment and
threaten public health. Therefore, it must be cleansed
of contaminants before being returned to our rivers and
lakes. The jars displayed along the side of the page show
wastewater at various stages of treatment, indicating
what the treatment process accomplishes: returning
safe, highly treated water back to the environment.
Protecting our Environment
The Wisconsin Department of Natural Resources (WDNR) and the
United States Environmental Protection Agency (EPA) have rules
governing the treatment of wastewater that establish standards for the
quality of water returned to the environment. The laboratory routinely
tests samples of wastewater to ensure that the plant is meeting these
standards. On a daily basis, the laboratory performs approximately 100
plant. The results are reported to the WDNR each month in accordance
with State laws. Ultimately, all of the testing is done to preserve and
protect our environment.
Treatment Plant History
The City of Watertown, located along the banks of the Rock River on the border between
Dodge and Jefferson Counties, obtained its charter in 1852. The ﬁrst sewer construction in
the City dates back to 1895.
The ﬁrst wastewater treatment plant, designed to treat 1.8 mgd, was placed into service
in 1933 on an island in the Rock River to address public health concerns and nuisance
conditions in the river. The plant was expanded up to a 2.5 mgd capacity in 1955, and
further expanded up to 5.2 mgd in 1980. Twenty years later, due to the plant’s age and
more stringent requirements for discharging to the Rock River, the City undertook a
comprehensive Facilities Plan. Completed in 2000, the Facilities Plan recommended that a
new treatment plant be constructed on a new 40-acre tract adjacent to the old plant site.
Design of the new facilities took place in 2001, with construction commencing in 2002.
Completed in 2004, the new 5.2 mgd plant is designed to meet the City’s needs through
the year 2024. The treatment plant site will accommodate future growth well beyond the
next twenty years.
Recycling – Processing and
Disposal of Biosolids
In the wastewater treatment process, a mixture
of naturally occurring microbes consumes
the pollutants and puriﬁes the water. As the
treatment progresses, an excess of microbial
solids is produced, called biosolids. The biosolids
undergo a fermentation process to stabilize
the material, killing potential pathogens and
reducing odor potential. The fermentation
process produces methane gas as a byproduct,
which is burned in boilers to produce the heat
needed for fermentation. The treated biosolids
are next dewatered to form a “cake” for storage.
The ﬁnished product is rich in nutrients and
organic material similar to peat, making it an
excellent soil additive for agricultural use. It
is tested extensively to make certain that all
WDNR and EPA regulations governing biosolids
use as a fertilizer are met. The material is then
spread on farm ﬁelds in the fall and spring,
depending on land availability. The recycling
of biosolids to agricultural lands represents an
use of resources.
optimal plant performance. The operators need accurate data to
monitor the status of plant components, making certain that
all of the various processes are running efﬁciently. Electronic
sensors are strategically placed throughout the plant to monitor
and control its state. A computer in each building collects data
from the sensors, communicating through a ﬁber-optic system
with the main Control Room in the Administration Building.
From the Control Room, the operators can observe the status of
system allows the operators to make decisions about adjusting
plant controls and scheduling equipment maintenance.
Trained operators ensure that the plant
runs at peak efﬁciency.
This building stores treated
biosolids, which form a “cake.”
Highly treated water is returned to the Rock River.
The City’s ﬁrst sewer line being
laid in 1895.
Photo courtesy of the Watertown Historical Society.