Wastewater treatment uses physical, biological, and chemical processes
to remove pollutants from water so it can safely be returned to the environment.
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.
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
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
For additional information on the wastewater treatment system please go to the
Wastewater Annual Consumer Confidence Report .
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