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 state’s 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 TRA’s 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:

• Water Environment Federation Outstanding Achievement in Water Quality Improvement Award

• Environmental Protection Agency Region 6 Award for Operations and Maintenance Excellence-Large Advanced Category

• Texas Natural Resource Conservation Commission Pinnacle Award for Operations and Maintenance Excellence-Large Advanced Category

• Multiple Gold and Silver Association of Metropolitan Sewerage Agency Award

• Water Environment Association of Texas Burke Facility Safety Award

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.

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.

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

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.

1. 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.
2. Administrative Services – The Administrative Services Department is responsible for accounting, administrative support, vendor coordination, human resources, information systems, inventory control, purchasing and training.
3. 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.

Central’s has the option of disposing of biosolids in an 80-acre on-site monofill.
 

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 System’s 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.

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

TRA’s 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.

Primary Treatment—The 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.

Secondary Treatment—Primary 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.

FILTRATION—Effluent water from the final clarifiers flows into continuous backwash gravity sand filters where solids are further removed.

CHLORINATION—Effluent from the carbon basins flows to the chlorine contact basins, where the water is chlorinated for disinfection.

CARBON—A majority of the effluent water is filtered through the carbon adsorption basin for reduction in toxicity. This provides a final polishing of the effluent.

DECHLORINATION—Effluent 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.

THICKENING—Primary 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.

DEWATERING—Sludge 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.

DISPOSAL—Sludge product from the dewatering process, now referred to as biosolids is beneficially reused in a land application program.