Wastewater treatment uses physical, biological, and chemical processes to remove pollutants from water so it can safely be returned to the environment.

Preliminary Treatment:
1. Water passes through screens to remove large plastics, wood, and other objects that are not biodegradable.

2. A grit removal system eliminates sand and grit.

3. A flow meter device provides flow data for operation of the plant process.

Secondary Treatment:
The wastewater is then divided between two Biological Treatment Units (BTU).

1. The wastewater enters a fermentation stage and mixes with return activated sludge from the secondary clarifier. The anaerobic conditions in this stage are stressful for certain microorganisms. These microorganisms under stress release phosphorus from their cells.

2. The next stage is the first anoxic stage, devoid of dissolved oxygen. When dissolved oxygen is unavailable, denitrifying microorganisms will use oxygen available in nitrates and release nitrogen gas.

3. The wastewater then enters the biological oxygen demand/nitrification stage. Dissolved oxygen is supplied in this stage for aerobic bacteria to accomplish three objectives. The microorganisms stabilize oxygen demanding organic material. The oxygen also nitrifies ammonia to nitrates and nitrites to allow for denitrification in the following anoxic stages. The microorganisms that released phosphorus in the initial stages, when placed in this non-stressed environment with oxygen, respond by storing more phosphorus.

4. Wastewater from this stage goes to the second anoxic stage where more denitrification takes place.

5. The wastewater is aerated to further strip nitrogen gas, oxidize remaining ammonia, and prevent the release of phosphorus.

6. The discharge from the BTU enters two secondary clarifiers. These units provide a quiescent environment, which allow solids to settle. The settled material contains the nutrient laden microorganisms. Most of these are circulated to the beginning of the BTU to provide microorganisms to repeat the processes. Some of the settled solids are removed from the system (wasted) and goes to the Solids Handling System. The clear water passes on to the Tertiary Treatment.

Tertiary Treatment:
1. The wastewater then passes through a deep bed filter system to further remove solid materials.

2. The clear effluent is disinfected using liquid chlorine.

3. The chlorine is removed from the effluent using sodium bisulfite.

4. In the final step, the wastewater is aerated.

The plant effluent is discharged through diffusers located in the Neuse River.

For additional information on the wastewater treatment system please go to the Wastewater Annual Consumer Confidence Report .

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