Wastewater Treatment Plant

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Wastewater treatment plant serving the community of Longview, Texas.

The City of Longview's Wastewater Treatment Plant is designed and permitted to treat an annual average flow of 21 million gallons per day (MGD) and has the ability to treat a 2-hour peak flow of 63 MGD of raw sewage.

The Sanitary Sewer Collection System transports raw sewage from the homes, commercial businesses, and industries to the Wastewater Treatment Plant. Twenty-one lift-stations support the gravity system of more than 800 miles of pipe by pumping the sewage through miles of force main to the Treatment Plant.

Treatment Process
The Texas Commission on Environmental Quality and the United States Environmental Protection Agency issue wastewater discharge permits, which establish the operating parameters for the treatment of wastewater. Wastewater Treatment can be broken down into several principal steps: Preliminary Treatment, Primary Treatment, Secondary Treatment, Advanced Treatment, and Sludge Treatment.

The purpose of the first step of the treatment process is to remove those materials from the wastewater that are untreatable or detrimental to treatment plant equipment or processes, such as large debris, and grit.

The purpose of primary treatment is to further remove materials from the wastewater through sedimentation. Sedimentation is the process by which solids and liquids are separated by gravitational forces. Denser solids called sludge settle to the bottom and lighter materials float to the top.

In the secondary treatment, the organic matter dissolved or suspended in the wastewater is stabilized by physical, chemical, or biological means. Two common types of secondary treatment are trickling filters and activated sludge. Both are biological processes which create the conditions favorable to the growth and reproduction of special microorganisms. The organisms consume the dissolved or suspended organic matter present. The microorganisms then settle out of the treated water. The dissolved oxygen content of the aeration basin is closely monitored. A certain level of dissolved oxygen is needed to maintain the proper levels of microorganisms.

Advanced treatment further reduces specific contaminants, organic matter, and suspended solids to very low concentrations to meet strict effluent standards and prepare the water for release into the Sabine River. Advanced treatment may be physical, chemical, biological, or a combination of the three.

Tertiary filters remove suspended particles not settled out in the clarifiers. The filters further enhance the final effluent prior to disinfection and discharge. The final treatment process is the ultra-violet (UV) disinfection system. The purpose of the UV disinfection is to prevent harmful bacteria and pathogenic organisms from leaving the plant along with the treated wastewater. The wastewater is exposed to light at a wave length of 254 nm.

After the UV process, the wastewater flows through a channel that aerates the water. From the channel the wastewater flows into Jackson's Cove, thence to Grace Creek and finally into the Sabine River.

Sludge is a by-product of the wastewater processes and is treated by stabilizing the organic material. This is accomplished by anaerobic digestion, which involves direct oxidation using a biologically active mass of organisms and oxidation of microbial cellular material by anaerobic bacteria. Other sludge processes are thickening, conditioning, dewatering and final disposal by land application at two permitted sites.