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Raw wastewater
(called influent) from the sewer system enters the
treatment plant at the headworks. Here, the wastewater
passes through two mechanical bar screens that remove
large debris, rags, sticks or other objects that may
damage equipment used in the treatment process. Wastewater
is then pumped to the Aerated Grit Chambers which removes
sand, gravel and metallic objects. The removal of these
solids improve treatment efficiency and help protect
the equipment against excessive wear. The Influent
then flows through a Parshall flume which measures
the flow rate and the total amount of wastewater treated
by the plant. |
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The clarifiers remove floatable
and settleable materials from the wastewater. The water
is detained in the clarifier for 3 hours which allows
the majority of solids (sludge) to separate from the
liquid portion and collect at the bottom of the tank.
The solids or sludge is then mechanically collected
and pumped to the digesters. Meanwhile, the floatable
waste (or scum) is skimmed off the top of the water
and is also pumped to the digesters. The remaining
liquid portion is pumped to the trickling filter. |
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Wastewater
is distributed over the honeycomb-like plastic filter
media which is covered with a thin bacterial growth.
Microorganisms grow on the media and absorb much of
the organic content found in the wastewater. When the
growth becomes too large, it breaks off and is passed
to the next phase of treatment. |
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This is the final treatment
step. The secondary clarifiers provide a quiescent
condition which promotes settling of the bacterial
growth from the trickling filters and also any solids
or scum not removed during primary sedimentation. The
collected sludge and scum are pumped back to the headworks
to repeat the treatment process. |
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Sludge collected from the
primary clarifiers is pumped to the digesters for treatment.
Sludge from the secondary clarifiers is routed backed
to the headworks and will repeat the treatment process.
No sludge is collected in the trickling filters |
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Collected sludge is pumped into heated
tanks called Digesters. Anaerobic (absence of oxygen)
bacteria thrive in the digesters, and convert raw sewage
sludge to an inert material (digested sludge), methane
gas and carbon dioxide. This process takes about two
to three weeks. |
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Digested sludge from the digesters is
distributed to the sludge drying beds. The liquid portion
of the sludge is evaporated or decanted and returned
back to the headworks to repeat the treatment process.
When the sludge has dried, it is tested for pollutants.
When approved, the sludge will be spread on the City’s
farm land where only restricted crops are grown (non-human
consumption). The dried sludge is categorized as Grade
B quality and is safe and relatively odor free. |
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Digester gas (approximately 60% methane,
40% carbon dioxide) is produced by anaerobic bacteria
in the digesters. The gas is collected and fuels two
engine generators each of which produces 400 kilowatts
of continuous electrical power for use in the treatment
plant. Waste heat recovered from the engine is used
to heat the digesters. |
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The operations building provides a central location
for plant personnel. It contains the main control room
which is used to operate and monitor the treatment
process. In addition, it contains offices, a laboratory,
and the lunch/training room. |
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The City’s treatment Plant 2 laboratory maintains
a Department of Health Services, Environmental laboratory
Accreditation Program (ELAP) Certificate No. 2001 in
the field of testing # 16 for conventional pollutants.
Influent, Pri-Effluent, and Final Effluent are analyzed
frequently to confirm the treatment plant is operating
as designed. |
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Final effluent is used to irrigate restricted agricultural
crops (non-human consumption). Crops consist mostly
of alfalfa hay, and cotton. The reservoirs store the
water until it is needed for irrigation and provides
a habitat for water loving fowl. |
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The City owns 5,000 acres located just south of
the Plant 2 treatment plant. The farm land is leased
to Progressive Associate Group which uses Plant 2 effluent
to irrigate restricted crops (non-human consumption)
such as cotton and alfalfa. Biosolids generated from
both Plant 2 and Plant 3 are spread on this farmland. |
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The City’s Wastewater Treatment Plant 2 also
provides service to indirect discharges by accepting
septage waste from residential septic tanks, seepage
pits, interceptor, cesspools, restaurant grease traps,
and chemical toilets. Only pre-authorized industrial
waste is accepted at the City’s treatment Plant
2. |
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