The Green Bay Facility was built in 1975. It was the first
wastewater treatment facility in the country to treat both
municipal and paper mill waste.
The Green Bay Facility is located on the mouth of the Fox River.
On average the facility receives about 30 million gallons per day
of wastewater from 17 surrounding communities and the Procter and
Gamble Paper Products Company.
Domestic wastewater arrives at the facility near the bottom the
Pump Station through a large (108") pipe called an interceptor. The
domestic wastewater enters the treatment where we remove objects
that are bigger than two and one-eighth inch in size, through one
of two course bar screens. The Pump Station also contains four
large pumps, which lifts the domestic wastewater to above ground
level to the next step in the treatment process.
There are three Mill pumps within the Pump Station that handle
wastewater from two nearby paper mills. The wastewater arrives
through a separate interceptor (42 " pipe). The "Mill Waste" is
pumped to the next step in the process and is then combined with
the domestic wastewater.
Headworks is often considered the beginning of the treatment
process at the Green Bay Facility. Within, step screens provide
preliminary treatment, and degritting equipment separates and
removes inorganic material (sand-like substances) from the waste
streams. Incoming wastewater passes through two fine screen step
screens, which trap debris. Once trapped, the solid objects are
removed, then washed and compacted before being emptied into a
bucket on the ground floor for removal to a landfill.
Once the wastewater has been screened in headworks the
wastewater flows into the primary clarifiers. The wastewater is
slowed and allows the solids that have been suspended in the water
to settle out. The floating material (scum and grease) will float
to the top and an arm skimmer circles the clarifier, collecting the
material for further processing. Nearly 60% of the solids are
removed before it moves on to the Aeration Basins.
In this step of the process, sometimes referred to as
"Secondary" or "Biological" treatment, bacteria and micro-organisms
growing in the aeration basins remove organic matter by consuming
it as food.
The aeration systems utilize a process commonly known as the
activated sludge process. The effluent from the primary clarifiers
flow into any one of the six aeration basins. We provide both food
(organic material) and air for the microorganisms to clean the
The air is supplied from a compressor through diffusers that lay
near the bottom of the basin. Each basin contains 5500
The activated sludge process currently utilized by GBMSD is
commonly known in the wastewater field as "single stage
nitrification/denitrification with biological phosphorus removal".
To properly operate the aeration systems, the operators at GBMSD
must insure sufficient numbers of microorganisms are present to
completely breakdown the influent waste, ammonia, and
After the wastewater leaves the aeration basins, it enters the
final clarifiers where any solid material is settled out to the
bottom of the basins.
The solids that settle out are either sent back to the aeration
basins (return activated sludge) or are "wasted" to the Gravity
Belt Thickeners (waste activated sludge).
The water that flows over the weirs is sent onto the
disinfection process for the final step in the treatment
This is the final step of the liquids treatment process. As the
wastewater prepares to leave the facility, a chemical is injected
into the water called sodium hypochlorite (similar to household
bleach) through a mixer at the very beginning of the disinfection
chamber. The mixer is used to help distribute the chemical evenly
in the water.
Next the water must flow through a series of four "passes" or
channels to make sure that there has been sufficient time and
contact to kill disease-causing bacteria. At the end of the last
pass, another chemical is added. This chemical is sodium bisulfite.
Sodium bisulfite is used to remove (neutralize) any residual
The effluent chlorine residual is monitored and controlled
through our computer control system. This system measures the
residual chlorine just prior to the injection of sodium bisulfite.
The equipment used to monitor the residual controls the amount of
sodium bisulfite used.
The treatment plant operators conduct tests to verify that the
residual chlorine has been removed from the effluent.
There are four gravity thickener basins. The basins receive
sludge and scum (stuff floating on top of the water in each basin)
flow from the four primary clarifiers along with the scum from the
ten final clarifiers.
The gravity thickeners provide a quiescent condition where the
primary sludge can settle to the bottom of the basin further
thickening the sludge prior to pumping to the sludge holding tanks
(SHT) in the solids processing building. The quiescent condition in
the gravity thickeners also allows the scum and grease to float to
the surface of the basin.
A rotating collector mechanism scrapes the bottom sludge toward
a center sump for removal and skims the floating material into a
scum manhole. Scum pumps transfer the scum from the manholes to the
scum concentrator in the solids building. This scum is then further
thickened and then pumped to the Incinerator as a fuel source.
The Gravity Belt Thickeners (GBT) are designed to thicken the
waste activated sludge which comes from the final clarifiers. To
aid in de-watering the sludge, a chemical called "polymer" is added
to the sludge at the front of the GBT. The sludge and the polymer
become bonded to each other thus causing "flocculation," where the
solids start to separate from the liquid. The sludge and polymer
flow onto a moving belt where the water and sludge start to
separate. The water falls through the porous weave of the belt
leaving the sludge behind. The water drains to a pan below the belt
and is pumped back to the beginning of the treatment process. The
sludge moves with the belt and is turned continuously by plow-like
devices called chicanes. The chicanes move the sludge back and
forth allowing the water to fall through the belt to the drain.
Near the end of the belt a ramp contacts the belt at its leading
edge, forcing the sludge to go up and over the ramp. This action
causes the sludge to roll back on itself. This rolling motion cases
further dewatering of the sludge. The ramp is adjustable to further
enhance the thickening of the sludge. The thickened sludge is sent
next to the Belt Filter Presses.
The solid materials (thickened Primary and Waste Activated
Sludges, and Septage) that are removed from the wastewater and
collected throughout the treatment process need to be dewatered, or
thickened, prior to their disposal.
The sludges are combined in Sludge Holding Tanks and mixed to
keep them well blended. The blended sludges are conditioned with
polymer before being fed onto the Belt Filter Presses (BFP). Only
two of the four BFPs are in operation at a time, with the remaining
two in stand-by.
The sludge is moved along the BFPs on a porous cloth belt, which
allows the water to drain through. The solids remain on top of the
belt, quickly concentrating as the water drains away. The BFPs have
a second belt at the end of the first where the solids are squeezed
between the two. The belts move through a series of rollers
applying more than 500 pounds of pressure, to squeeze out as much
water as possible. The solids coming off of the BFPs are referred
to as dewatered "cake" and are conveyed to the incinerators.
Prior to disposal in local sanitary landfills, the dewatered
belt filter press sludge is burned to an ash within multiple hearth
incinerators. Burning the sludge cake reduces the weight and
volume, resulting in less expensive landfill hauling fees.
Incineration at the Green Bay Facility takes place on a nearly
continuous basis. Typically, one incinerator operates for a
three-month period, while the other unit receives any required
maintenance. Then it sits idle until the rotation occurs once
again. Control and monitoring of the incineration systems takes
place from within the solids building control room.
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