City of Grand Prairie facilities are now open for public access with safety precautionsGet the latest COVID-19 information...

What is wastewater?

You may not realize what happens after you wash something down the drain or flush the toilet. That sewage or wastewater is conveyed in an extensive underground collection system comprised of piping from your house, your place of business and any other place plumbed to the sanitary sewer.

The wastewater collection system (totally separate from the storm water collection system that collects storm run-off from streets and parking lots) collects the wastewater and carries it to the wastewater treatment plant.

Sewage is the wastewater released by residences, businesses and industries in the community. It is 99.94% water and only 0.06% solid material. Sewage contains nutrients (such as ammonia and phosphorus), minerals and metals. Sewage treatment is a multi-stage process to treat wastewater before it reenters a body of water, is applied to the land or is reused. The goal is to reduce or remove organic matter, solids, nutrients, disease-causing organisms and other pollutants from wastewater.

Wastewater Process Infographic: Water is filtered back into river after arriving at water treatment center through the pipes and undergoing screening stage and primary, secondary and final treatment stages

Preliminary Treatment

Preliminary treatment to screen out, grind up, or separate debris is the first step in wastewater treatment. Sticks, rags, large food particles, sand, gravel, toys, etc., are removed at this stage to protect the pumping and other equipment in the treatment plant. The collected debris is usually disposed of in a landfill.

Primary Treatment

Primary treatment is the second step in treatment and separates suspended solids and greases from wastewater. Wastewater is held in a quiet tank for several hours allowing the particles to settle to the bottom and the greases to float to the top. The solids drawn off the bottom and skimmed off the top receive further treatment as sludge. The clarified wastewater flows on to the next stage of wastewater treatment.

Secondary Treatment

Secondary treatment is a biological treatment process to remove organic matter from wastewater. Microorganisms are cultivated and added to the wastewater. The microorganisms absorb organic matter from sewage as their food supply.

Final Treatment

Final treatment focuses on removal of disease-causing organisms from wastewater. Treated wastewater can be disinfected by adding chlorine or by using ultraviolet light. High levels of chlorine may be harmful to aquatic life in receiving streams. Treatment systems often add a chlorine-neutralizing chemical to the treated wastewater before stream discharge.

Advanced Treatment

Advanced treatment is necessary in some treatment systems to remove nutrients from wastewater. Chemicals are sometimes added during the treatment process to help settle out or strip out phosphorus or nitrogen.


Sludges are generated through the sewage treatment process. The goals of sludge treatment are to stabilize the sludge and reduce odors, to remove water to reduce volume, to decompose some of the organic matter to reduce volume, and to disinfect the sludge to kill disease causing organisms. Depending on the contaminant level in the treated sludge, it is either disposed of in a landfill or used as fertilizer for non-food grade crops.


Wastewater treatment processes require careful management to ensure the protection of the water body that receives the discharge. Trained and certified treatment plant operators measure and monitor the incoming sewage, the treatment process and the final effluent.

The City of Grand Prairie is part of the Central Regional Wastewater System run by the Trinity River Authority (TRA). All of the wastewater generated in the City runs into the TRA’s collection system to the TRA Central Treatment Plant located at 6500 W. Singleton Blvd. on the edge of Grand Prairie at I-30 and Loop 12. The treatment plant takes in wastewater, treats it, and discharges it to the Trinity River.