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Last Updated: June 16, 2009 |
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The domestic wastewater first goes to the primary plant and undergoes
primary treatment and chlorination. The industrial wastewater
which is 85% of the total flow, feeds directly into the regional
facility. Wastewater first flows through three bar screens.
These screens filter out larger particles, and the water then flows
through the parallel grit chambers. Grit chambers use the forces
of gravity to remove smaller, heavier particles like gravel and sand by
decreasing the velocity of the flow. From there the flow enters
the Parshall flumes which measure the rate of flow. The flow then
enters primary treatment which consists of eight clarifiers.
Primary treatment removes the settleable and floatable solids from the
wastewater.
The flow then enters secondary treatment which is biological rather
than physical as in the previous stages of treatment. In this
stage, bacteria consume most of the remaining waste materials. To
sustain the growth of this bacteria, oxygen is added to the wastewater
in one of four sealed pure oxygen reactors. This oxygen is
produced in an on-site cryogenic plant. After a few hours, the
water flows into sedimentation tanks where solids settle to the
bottom. This completes the secondary phase of treatment. At
this point 90-95% of the pollutants have been removed from the
wastewater.
Throughout the wastewater treatment process, solids have been
removed from the wastewater. These solids are called sludge or
biosolids and require further processing. The goal in processing
sludge is to take as much water out of it as possible and to return the
water to the river in an environmentally safe state. To remove
the water from sludge, it is pumped into gravity thickeners.
These thickeners also use the force of gravity to separate water from
these solids. The sludge is placed in a holding tank at this
point. The waste activated or biological sludge is sent through
air flotation thickeners which thicken waste-activated sludge. It
then goes to a holding tank where it is blended with the primary
sludge. The solids handling system at the plant consists of gravity
thickening of primary sludge and dissolved air flotation thickening of
Waste Activated Sludge (WAS), followed by treatment using a dry solid
centrifuge, polymer feed system and multiple hearth incineration.
Ash from the incinerator is then disposed of in an approved landfill,
safely returning the materials to the environment.
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