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PROCESS OF WASTEWATER TREATMENT PLANT
Wastewater enters the treatment plant
First it goes through a fine screen, next to aerated
grit chamber, and then enters the primary clarifier. Sludge
settled in the primary clarifier is sent to the fermenters
and then to digesters.
After the primary treatment, wastewater flows into (BNR)
bioreactors.
The activated sludge is separated in the following secondary
clarifier. The clear effluent flows into Ultraviolet (UV),
then to River. Settled activated sludge in the secondary
clarifier is pumped back to BNR.
Excess sludge is pumped into the dissolved air floatation (DAF)
unit for thickening.
Wastewater is collected in sanitary sewers (a complex
network of underground pipes). Upon reaching the treatment
plant, the wastewater flows through a series of treatment
processes which remove the wastes from the water. Each step
the water becomes cleaner.
Grit Removal
In the grit chamber, heavy particles, such as a small
stones, eggs shells, and coffee grounds settle to the bottom
and are removed. These abrasive materials can damage pumps
and cause equipment to fail prematurely the grit is removed
and washed in the grit classifier before it is properly
disposed.
Preliminary Treatment
Bar screens catch rags, sticks, plastic containers, and
other objects floating in these large items are removed so
that they do not clog pumps or interfere with other
equipment process.
Primary sedimentation tank
In the primary sedimentation or "settling" tank, heavier
solids are given time to sink to the bottom. These solids
called "primary sludge" are sucked out of the bottom of the
tank. They are sent to a digester for further treatment.
Oil, grease, and other scum that float of the wastewater are
skimmed off and may be sent to the digester.
Fermenters
The fermenters are large and closed tanks with a rotating
stirring mechanism. Sludge is fermented to produce the
volatile fatty acids (VFAs) .The residual sludge along with
scum is pumped to the sludge digesters . The foul air also
functions as a supplementary air supply for the bioreactors.
Dissolved air floating (DAF) tank
Waste activated sludge is thickened in dissolved air
floatation (DAF) tank to reduce the volume of sludge.
Under the effect of air bubbles flowing upwards, the sludge
solids are carried to surface and skimmed out.
Anaerobic Sludge Digester
Anaerobic digestion is biological process which break down a
significant amount of organic solids in the sludge and at
the same time produces methane gas
BNR bioreactors
The bioreactor is divided into several cells. In some cells,
air/ oxygen is introduced through diffusers in removing
pollutants such as BOD; while in other cells, no air is
required to remove nitrogen and phosphorus .
The pollutants serve as the food source to maintain the
metabolism of the microorganisms.
Ammonia is released into the atmosphere. Phosphorus becomes
part of the plant biosolids (Sludge).
Secondary sedimentation tank
The sludge from the bioreactors flows to large circular
clarifier. Settled activated sludge is then pumped back to
the bioreactor and excess activated sludge is pumped to the
dissolved air flotation.
Disinfection
Clarified supernatant from the secondary clarifiers flows
through the Ultraviolet (UV) light disinfection unit, and
then discharged to the River. |