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| Ten Mile Creek Regional Wastewater
System The Ten Mile Creek
Regional Wastewater System went into service for the first time in November 1970. This
advanced wastewater collection and treatment facility provides service for an
85-square-mile service area in southern Dallas and northern Ellis Counties.
Contracting parties served by TRA’s Ten Mile Creek System include Cedar Hill, De
Soto, Duncanville, Lancaster and Ferris. In excess of 110,000 citizens of these cities are
served by the Authority.
The treatment plant for this system was developed on a 100-acre tract of land a short
distance northeast of Ferris and had an initial treatment capacity of 6.78 million gallons
per day. In the early 1980’s substantial growth within the customer cities
resulted in TRA planning and constructing treatment plant expansions. |
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The first, or Phase I expansion was completed in August 1986 and increased the
plant’s rated capacity
to 11.5 MGD. The Phase II expansion was completed in
May 1988
and increased treatment plant
capacity to 20 MGD.
Phase III construction was completed in September 1989. This construction basically
involved the rehabilitation and refurbishment of the major components from the original
6.78 MGD treatment plant.
In its current configuration, the Ten Mile Creek Treatment Plant operates as two separate treatment trains. Components of the first train include those that were constructed as
part of the Phase I construction program and of the original 6.78 MGD plant, ultimately
refurbished under the Phase III construction. The second treatment train includes the new
treatment components added under the Phase II construction programs which increased the
plant’s treatment capacity to 20 MGD. Phase IV &
Phase V construction projects
have renovated and refurbished components of the
entire plant to provide for more
efficient operation.
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The Ten Mile Creek Plant is capable of
treating wastewater to a 97 percent level of purity as compared to raw wastewater entering
the plant. The system’s discharge permit specifically requires that the final
discharge from the plant contain no more than 10 milligrams per liter of biochemical
oxygen demand, 15 mg/l of total suspended solids and a seasonal limitation of 5 mg/l of
ammonia in the winter months and 3 mg/l of ammonia in the summer months.
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Each customer city owns
and operates its own internal collection system which discharges into TRA’s Ten Mile
Creek interceptor system. The Authority’s interceptor pipelines extend for
approximately 33 miles not including parallel lines that have been added and will continue
to be added to accommodate additional wastewater flows generated by growth within the
service area. Flows entering TRA’s pipelines are metered so that customer cities are
only charged for their pro rata share of system use and costs. |
The Ten Mile Creek Regional Wastewater
System has long been recognized by both state and federal regulatory agencies as one of
the best treatment systems in the state. The system’s ability to consistently meet or
exceed the stringent parameters of its wastewater discharge permit was further documented
when it received the Gold Award from the Association of Metropolitan Sewerage Agencies
every year since 1987 except 1994 and 1995 when it received the Silver Award. |
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Treatment Process OverviewLiquids Process
Primary Treatment—As wastewater flows enter the treatment plant, large debris and
other materials are screened out to prevent damage to pump stations downstream. Following
this, the raw wastewater is lifted by pumping stations to the plants’ four circular
primary clarifiers. When wastewater enters the primary clarifiers the flow is slowed to
permit gravity separation of solids. Solids that either float or settle are separated and
removed from the wastewater stream during primary treatment. Solids remaining in the
wastewater flow at this point are either suspended or dissolved and will be removed in
later phases of the treatment process.
Secondary Treatment—The treatment plant’s eight aeration basins represent
the heart of the activated sludge method of secondary treatment. Through the use of
mechanical aerators and compressed air diffusers, dissolved oxygen is mixed with the
partially treated flows to provide oxygen for the support of microorganisms at optimal
levels. The microorganisms consume the majority of the organic contaminants remaining in
the wastewater.
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The next stop for
the wastewater in the treatment process is final clarification
where the effluent from the aeration basins is returned to a
relatively calm state. The final clarifiers allow the
microorganisms to separate and settle to form a sludge blanket
on the floor of the basin. The resulting effluent water becomes
very clear. The sludge blanket is removed from the clarifier and
sent to the thickener or returned to the front of the aeration
basin in order to sustain the biological treatment |
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process. The
microorganism population is controlled by how much of the
sludge blanket is returned.
Advanced
Treatment -- Effluent water from the final clarifiers next
flows into the plant's eight automatic backwash sand filters
where it is polished even further. These filters use silica
sand to filter out most of the remaining
impurities.
Effluent from the sand filters
is next introduced into the plant's chlorine contact chambers
for disinfection. Finally, the effluent is dechlorinated
before it is discharged into Ten Mile
Creek.
Solids
Handling
Degritting --
When sludge is
removed from the wastewater stream in the plant's primary
clarifier, it is necessary to remove the accumulated grit from
the primary sludge. The degritting process is accomplished by
the dorrclone system and sedimentation. This procedure plays a
vital role in increasing the service life of pumps downstream
of this process due to the abrasive qualities of
grit.
Thickening -- After mixing the
primary and waste activated sludge, the thickening process is
completed by bringing the sludge to a still state in the
sludge thickeners so sedimentation may occur. Thickening is
crucial because it reduces the water content of the sludge and
thereby reduces the total volume requiring further
processing.
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Digestion -- Thickened sludge from the gravity thickener is next
processed in four anaerobic digesters. The digestion process breaks
down the organic content of the sludge into stable compounds.
Methane gas produced during the digestion process is recovered and
used as fuel for the boilers which maintain the digesters at an
optimal operating temperature. |
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Sludge Lagoons -- Approximately 35 acres adjacent
to the treatment plant store the inert digested sludge in
three separate cells created by levees. Liquid from the
digested sludge is decanted from the lagoons and gravity flows
back to the head of the plant for treatment, leaving the
residual fully treated sludge to dry. Dried sludge is disposed
of in a landfill.
Surface Disposal Cells --
Approximately 25 acres adjacent to the treatment plant store
the inert digested sludge in three separate cells created by
levees. Liquid from the digested sludge is decanted from the
surface disposal cells and gravity flows back to the head of
the plant for treatment, leaving the residual fully treated
sludge to dry. Dried slug is disposal of in a landfill.
Trinity River Authority of Texas
Ten Mile Creek Regional Wastewater System
(972) 225-3462 |
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