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Property: Density By Megan Water Treatment Stages Flush/Wash down: When
wastes are deposited into a toilet, the solids settle or sink first. This
is because the solid waste has a higher density because its particles
are so tightly packed together. The density of the water is lower because
they are spread apart more than the solid. Pipes: When the wastes
are traveling through the pipes the solid waste is behind the liquid waste
because the liquid’s particles are farther apart and bouncing of
the walls of the pipe pushing it forward so it flows faster. The solids’
particles are closer together therefore the stay put, so there has to
be another force pushing it through the pipes like the less dense liquid. Physical Rake screen and Aerated
Grit Chambers: In the screening stage the large inorganic solids are
taken out by screens called rakes, they are taken out of the water easily
because their particles are so close to one another, making them have
a higher density in the water so they easily get caught in the rakes and
are taken away. In the aerated grit chambers more inorganic solids are
removed, but they are of the smaller variety: they remove things such
as grit, sand, gravel and dirt. These stages remove the inorganic objects
with high densities. Primary Clarifiers:
The scum and oil have a lower density than the rest of the wastewater
so they float to the top. The organic sludge, or human waste, has a higher
density than the water so it sinks to the bottom. The floating scum and
grease are skimmed off the top, and the sunken sludge is scraped off the
bottom and pumped into gravity thickeners. The remaining wastewater, called
primary effluent, goes to aeration tanks and bioreactors for the first
and second stages of the secondary treatment. Biological Secondary Clarifier: The primary effluent is mixed with air, bacteria and other microorganisms in the aeration tanks and bioreactors. The micro organism float around in the water, but don’t sink or float on top of the water because their density is very close to the same as the wastewater. The bacteria and microorganisms feed off the organic materials left in the primary effluent, therefore purifying the water. Compressed air is injected into the activated sludge near the bottom of the aeration tanks and bioreactors. The microorganisms are mixed
by the injected air and are brought into contact with the organic materials.
This mixture is called mixed liquor. In the secondary clarifiers, the
activated sludge falls because its particles are packed more closely together
than the rest of the water sinks to the bottom, and more scum and grease
are skimmed off the top because they have a lower density than the water,
their particles are not as big and not packed close together. Chemical Tertiary: Liquid aluminum
sulfate (liquid alum) is added to the mixed liquor. This is called the
chemical precipitation process. The aluminum phosphate formed settles
to the bottom because of its higher density than the wastewater. The particles
are a larger size and packed closer together than the water particles.
The aluminum phosphate is then pumped with the waste activated sludge
to the dissolved-air flotation tanks. This process does not remove any
ammonia or nitrogen from the wastewater. Stages Density does not
apply to: Biological-Phosphate and Nitrogen
Removal |