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 The
Trinity River basin lies in the eastern half of Texas and has an overall length of 327 air
miles. The total area drained by the Trinity River and its tributaries is 17,969 square
miles, or approximately 6 percent of the states land area. Approximately three and one-half million people are served by eight major regional
wastewater treatment plants operated by the Trinity River Authority, Dallas, Fort Worth,
Garland and the North Texas Municipal Water District. Wastewater facilities operated by
these entities release more than 500 million gallons per day of treated wastewater that
has 98 percent of all conventional contaminants removed. As a result of our combined
efforts, the Trinity River is once again, beginning to resemble a river. The
Authority has proven that the concept of regionalized treatment of
wastewater works and works well to the benefit of all parties. That concept first began
with the construction of TRAs Central Regional Wastewater System. Other similar
Authority wastewater projects, now on line, are providing these same valuable services.
Read about them..................
Central Regional Wastewater System Winner of the following awards:
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Water Environment Federation
Outstanding Achievement in Water Quality Improvement Award
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Environmental Protection Agency
Region 6 Award for Operations and Maintenance Excellence-Large Advanced Category
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Texas Natural Resource Conservation
Commission Pinnacle Award for Operations and Maintenance Excellence-Large Advanced
Category
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Multiple Gold and Silver Association
of Metropolitan Sewerage Agency Award
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Water Environment Association of
Texas Burke Facility Safety Award
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System Overview The Trinity River Authority is a political
subdivision of the state of Texas and encompasses all of five and parts of 12 counties
located within the Trinity River Basin. Public services currently provided and/or being
developed by the Authority include multiple regional wastewater treatment, water
treatment, recreation, water supply and reservoir systems. In 1957, the Trinity River Authority established
the Central Regional Wastewater System. In December 1959, the Central Regional Treatment
Plant was placed into operation to serve four member cities: Irving, Grand Prairie,
Farmers Branch and a portion of western Dallas. During the late 1960s and early 1970s, the Central
Regional Wastewater System expanded its original 28-mile pipeline to approximately 140
miles that extended services to several other cities. More recently, expansion has
extended the pipeline system (collection system) to over 200 miles serving all or part of
21 contracting parties with almost one million people being served. In 1972, the
federal government passed the Federal
Water Pollution Control Act that established much higher standards for wastewater
treatment. To meet the new standards and to accommodate an ever expanding service area,
the Central Regional Treatment Plant capacity was expanded to 100 million gallons per day
(MGD). Secondary and tertiary treatment capabilities (activated sludge and filtration)
were added to provide the more stringent level of treatment required. In 1993, the CRWS Plant
was expanded to 162 MGD capacity with total secondary and tertiary treatment and the ability to treat a 2-hour
peak of 335 MGD. Also, dechlorination facilities were added to meet new state and federal
guidelines for the removal of chlorine to less than 0.1 mg/l.
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Making it Work with Technology, People and Programs Technology
State-of-the-art technology makes the
Trinity River Authority Central Regional Wastewater System efficient and
economical. The Central System has a service area of over 450 square miles
with a collection system extending more than 200 miles. The system uses
current state-of-the-art technology in collection system telemetering,
computer systems, operational control and maintenance management.
A process computer system receives all collection system meter stations
and lift stations flows, and also controls and monitors various
functions of the plant process. |
Additionally, the process computer
retrieves vital
process information within seconds after it occurs. This is accomplished by strategically
placed input and output points that the computer controls and monitors throughout the
plant. The inventory control, purchasing, pretreatment, laboratory and maintenance
management functions operate on computer systems with customized software programs
providing information used in the decision-making process. |
Odor Control Odor control processes include chemical addition of
iron salts for treatment of sulfides in solution and modifications to the primary sections
of the process to reduce the hydraulic free fall of wastewater that releases hydrogen
sulfide gas to the atmosphere. Foul air is collected throughout the plant and
processed though specially-constructed biofilters for
biological treatment to reduce odors to acceptable levels. Secondary activated sludge can
also be returned to the front of the primary process to reduce high loadings of sulfide in
the influent wastewater during odorous periods. The on-site monofill and biosolids staging
facilities have extensive neutralization dispersing equipment, which is utilized to
control odors at these areas. A sludge management pump station collects all residual
sludge from the biosolids staging area and returns the side stream to the front of the
plant.
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Toxicity Reduction Both state and federal permitting agencies
require
whole effluent toxicity testing of the wastewater discharged to the Trinity River. The
reduction of toxicity to extremely low levels is required to protect the aquatic organisms
in the receiving stream and test species. Controlling toxicity begins at its source and an
aggressive Pretreatment Program implemented by the Central Project for industrial
discharges has
been instrumental in minimizing toxic
compounds in the influent wastewater. Also,
optimizing process operations throughout the treatment train produces a
secondary treated wastewater that consistently falls below acute and
chronic toxicity levels for the specified test |

Page 3-1: Biomonitoringto
pass regulatory requirements, the EPA designated organisms, Ceriodaphnia dubia and Daphnia
pulex, must survive and reproduce in Central effluent. |
species. To insure wastewater toxicity is at an acceptable low level,
the secondary wastewater is pumped through nine upflow carbon absorption basins. The carbon beds have been in operation since 1989
and are among the largest successful operating units in the United States. The carbon
adsorption basins have clearly demonstrated throughout their operational history the
ability to reduce toxicity to an acceptable level and meet the stringent permit
requirements. |
Technology is only as good as the
people who are responsible for operating and maintaining the equipment. Central is staffed
with professional, dedicated personnel that take pride in their work. The plant staff has
an average length of service over six years, and includes a wide range of diversity in the
varied skills required at the Central Facility.
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The Central Regional
Wastewater System is organized into three departments and their functions are as follows:- System Operation and Maintenance
The
Operation and Maintenance Department is responsible for the complete operation and
maintenance of liquids and solids treatment process and equipment, lift stations,
electrical and electronics, grounds and vehicles.- Administrative Services
The
Administrative Services Department is responsible for accounting, administrative support,
vendor coordination, human resources, information systems, inventory control, purchasing
and training.- Technical Services
The Technical Services
Department is responsible for all process laboratory analysis and the interceptor pipeline
system, engineering, metering, monitoring and industrial pretreatment coordination. In
addition, the laboratory and pretreatment areas perform outside contract services for
other TRA projects and contracting parties.
In summary, it requires the coordinated individual
effort of dedicated employees having a wide range of skills to operate the system. These
employees take great pride in providing a vital service to the communities that are
members of the system. Programs To achieve and maintain cost-effective operations,
the Central System uses a program approach to achieving both long and short-term goals.
Project wide employee participation in these programs insures success and an opportunity
for personnel to develop and use skills. Typically, these programs transcend departmental
boundaries and benefit the system as a whole in areas such as safety, cost reduction,
emergency planning, plant appearance, etc. The preventative maintenance program consists of
planned maintenance activities that are scheduled by a computerized maintenance management
system. This system directly interfaces with the maintenance work order system and tracks
activities and associated cost. Predictive maintenance utilizes vibration-based machinery
monitoring, infrared thermography and oil and lubrication analysis. Proactive maintenance
is a management tool applied toward advanced investigative and corrective technology in
solving the root cause of equipment failure. The goal of this program is to reduce
equipment failures, extend its life and lower overall maintenance cost. Various programs at Central to improve overall
efficiency are: recycling of Freon, antifreeze, oil, paper, cans, glass and beneficial
reuse of biosolids. Dewatered sludges are processed at the biosolids
staging area to produce a beneficial product that is applied at predetermined agronomic
rates for the agriculture site. Dewatered sludge from the filter and belt press operations
meet class "A" biosolids requirements and are 90% below the maximum ceiling
limit established by both federal and state regulatory agencies for metals. Additional
quicklime is utilized, if required, in the stabilization/pasteurization process to produce
a class "A" biosolid. Centrals has the option of disposing of
biosolids in an 80-acre on-site monofill.
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| Contracting Parties TRA management directs the planning, design, construction
and operational strategies with the advice and input of the Central System Advisory
Committee. This committee is composed of one voting member from each of the Systems
21 contracting parties. All decisions which affect service, operations, capital costs and
the annual operating budgets are presented and discussed with this committee before final
action is taken by the TRA Board of Directors. |

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This teamwork approach to
problem solving produces a synergism in the decision-making process of this project.
All contracting parties pay the same cost for wholesale wastewater treatment, which is
currently in the range of $1.04 per 1,000 gallons. Payments to TRA are based upon
estimated costs and predicted allocations among the 21 parties. At the end of each fiscal
year, an audited settle-up procedure returns all unspent funds to the 21 parties.Emergency Response The Central Plant has a comprehensive Emergency
Response Plan to protect employees and the general public. There are four response teams
made up of eight members who are trained to contain chemical leaks at the Central
Facility. These response teams use state-of-the-art emergency equipment when called into
action. A safety trailer for responding to on-site emergencies is available to the
emergency responders. The response team is also fully trained in all rescue techniques and
confined space procedures. Process Overview TRAs Central System is not only a very large
collection and water reclamation unit capable of producing a very high quality effluent,
but is also a full service facility that possesses in-house capability to accommodate
virtually all of its operations, maintenance, administration and technical service needs. Complete treatment can be provided to monthly
average flows of 162 MGD and daily maximum flows of 335 MGD. During the treatment process,
biological oxygen demand, suspended solids and ammonia nitrogen are reduced by 99 percent.
The Central plant has the mechanical dewatering capability of processing 200 dry tons of
sludge daily. Unique features you will find within the Central
System include: - A fully integrated environmental laboratory provides
complete analytical capabilities for plant process monitoring and control for liquids and
solids operation around the clock.
- A full service industrial pretreatment division
whose services include industrial permitting, inspecting and sampling, which when coupled
with the analytical capabilities of the laboratory provide the Central system and its
customer cities with the ability to comply with all state and federal pretreatment laws.
- It is one of the few treatment facilities with
on-site biomonitoring facilities which provide a broad range of toxicity testing
capabilities.
- It features one of the largest successful carbon
adsorption processes in active use that consistently produces a nontoxic high quality
effluent water.
- The capability for in-house collection system
monitoring and repair.
- The largest urban effluent reclamation and reuse
program in Texas.
- Sludge dewatering using filter and belt presses
produces a dry product which allows for the full array of disposal options.
- An innovative odor control program involving the
collection, transportation and introduction of odorous gases into either the activated
sludge process or biofilters for biological treatment as a primary method of odor
reduction.
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| How Central Works Primary TreatmentThe primary process consists of
three steps. First, foreign objects are screened out of the wastewater to prevent damage
to downstream equipment. Second, the screened wastewater is pumped to the aerated grit
basins or pista grit systems where small particles, such as sand, gravel and other
abrasive materials, are removed and disposed. |

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| Third, wastewater flows
to the primary clarifiers, where the flow is slowed to allow gravity separation of
solids. Solids that settle or float are separated and removed from the wastewater stream.
Solids remaining in the wastewater are either suspended or dissolved solids. Secondary TreatmentPrimary treated wastewater
is evenly distributed into the aeration basins which utilize the activated sludge process.
At the bottom of the basins, a network of air distribution pipes and fine bubble diffusers
release minute air bubbles to provide mixing and oxygen for billions of microorganisms
within this process. The microorganisms consume most of the organic contaminants in the
wastewater. Final clarifiers allow the microorganisms to separate from the water and
settle on the basin floor to form a sludge blanket, ultimately producing clean effluent
water. The sludge blanket is removed from the basin floor by floating bridges that return
the sludge to the front of the aeration basin, which sustains the activated sludge
process. The microorganism population is controlled by removing a small percentage to
solids thickening. |
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Advanced Treatment FILTRATIONEffluent water from the final
clarifiers flows into continuous backwash gravity sand filters where solids are further
removed. CHLORINATIONEffluent from the carbon
basins flows to the chlorine contact basins, where the water is chlorinated for
disinfection. CARBONA majority of the effluent water
is filtered through the carbon adsorption basin for reduction in toxicity. This provides a
final polishing of the effluent. DECHLORINATIONEffluent from the
chlorine contact basins flows to the dechlorination channel where sulfur dioxide is added
to remove chlorine residual to less than 0.1 mg/l. Solids Handling THICKENINGPrimary sludge consists of the
solids that were separated by gravity settling in primary treatment. The activated sludge
process produces excess microorganisms (i.e. waste activated sludge), commonly called
secondary sludge. Primary and secondary sludges are thickened in gravity thickeners,
dissolved air flotation thickeners or gravity belt thickeners. DEWATERINGSludge from both the gravity
and dissolved air flotation thickeners are blended and conditioned with lime and ferric
chloride before being pumped under pressure into one of the three filter presses in the
sludge dewatering process. The sludge is dewatered to a cake with approximate dryness of
34 percent. Additionally, anaerobically digested sludge is mixed with primary and
secondary sludges. A portion of the sludge is dewatered using a single two-meter belt
press to a 20 percent dryness. DISPOSALSludge product from the
dewatering process, now referred to as biosolids is beneficially reused in a land
application program.
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Trinity River Authority of Texas Central Regional Wastewater System (972) 263-2251 Fax: (972) 331-4412 | 
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