Transcript Slide 1

Waste Water Treatment Plant
HOW DO TREATMENT PLANTS
PROTECT OUR WATER?
• Wastewater treatment plants:
• Remove solids, everything from rags and plastics to
sand and smaller particles found in wastewater;
• Reduce organic matter and pollutants--naturally
occurring helpful bacteria and other microorganisms
consume organic matter in wastewater and are then
separated from the water; and,
• Restore oxygen--the treatment process ensures that
the water put back into our rivers or lakes has enough
oxygen to support life.
WHERE DOES WASTEWATER
COME FROM?
• Homes--human and household wastes from toilets,
sinks, baths, dishwashers, garbage grinders, clothes
washers and drains.
• Industry, Schools, and Business--chemical and other
wastes from factories, food-service operations, school
activities, hospitals, shopping centers, etc.
• Storm Water Infiltration and Inflow from Runoff and
Groundwater--water that enters the sanitary sewer
system during a storm, as well as groundwater that
enters through cracks in sewers. The City of Columbia
has one set of sewers for wastewater from homes
and businesses (sanitary sewers) and a separate
system for storm water runoff.
Sanitary Sewers
• They carry wastewater
from homes and
businesses to the raw
wastewater pumping
station at the treatment
plant. The wastewater
flows by gravity, rather
than pressurized pipe
flow, in the sanitary sewer
pipes. Routine cleaning
and closed circuit
television inspection of
sanitary sewer lines helps
keep the sewer collection
system in good shape.
Bar Screens
• They let water pass, but
not trash (such as rags,
diapers, etc.). There are
two bar screens located
inside the Raw
Wastewater Pump
Building. The trash is
collected and properly
disposed of. The
screened wastewater is
pumped to the Primary
Settling Basins.
Primary Settling Basins
• They allow smaller
particles to settle from
wastewater by
gravity. This primary
wastewater flows out to
the next stage of
treatment. Scrapers
collect the solid matter
that remains (called
"primary sludge"). A
surface skimmer collects
scum or grease floating
on top of the basins.
Aeration Basins
•
They supply large amounts of air
to the mixture of primary
wastewater and helpful bacteria
and the other microorganisms that
consume the harmful organic
matter. The growth of the helpful
microorganisms is speeded up by
vigorous mixing of air (aeration)
with the concentrated
microorganisms (activated sludge)
and the wastewater. Adequate
oxygen is supplied to support the
biological process at a very active
level. The ratio of food (organic
matter) to organisms to oxygen is
continually monitored and
adjusted to meet daily variations in
the wastewater.
Final Settling Basins
• They allow the clumps of
biological mass (the
microorganisms) to settle
from the water by
gravity. 90-95 % of this
mixture, called "activated
sludge," is returned to the
aeration basins to help
maintain the needed
amount of
microorganisms. The
remaining 5-10 % is
pumped to the anaerobic
digester (described
later).
primary sludge
• The "primary sludge"
from the Primary Settling
Basins is pumped to the
Hydrocyclone Grit
Separator where it is
spun, thereby separating
the inorganic solids (grit)
from the lighter weight
organic solids. The grit is
disposed of in the City
landfill.
primary sludge
• The primary sludge continues
on to the gravity Sludge
Thickener where the solids
are concentrated and pumped
to the anaerobic
digesters. The liquid overflow
is returned to the pump
station. Waste Activated
Sludge from the Final Settling
Basins is pumped to a
Centrifuge (image at right)
for further solids processing,
then pumped to the anaerobic
digesters.
Digesters
• Primary and activated
sludges are
anaerobically digested
(decomposed by bacteria
without the presence of
air) in the two-stage
digesters. Stabilized
sludge has little odor and
conforms to the EPA
requirements to further
reduce harmful
microorganisms
• Digestion at 35ºC
Digesters
• Methane gas is produced by
this anaerobic digestion and is
used as fuel for an enginegenerator providing 240 kW of
electrical power used in the
treatment process. Waste
heat from the engine is
recovered for heating the
treatment plant buildings and
to provide heating to improve
the sludge digestion process
and produce more gas.
subsurface injection
• application of the stabilized sludge (biosolids)
onto both City-owned and private farmland by
subsurface injection (plowing). The biosolids
are utilized in an environmentally acceptable
manner as a beneficial and valuable fertilizer
and soil conditioner. The biosolids applied to all
sites are monitored for nutrients, metals, other
compounds and fecal coliform bacteria. Soil
testing is performed at all sites prior to biosolids
application.
The End
• Thanks for your attention