Pump Station

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

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.

Primary Clarifiers

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.

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 wastewater.

The air is supplied from a compressor through diffusers that lay near the bottom of the basin. Each basin contains 5500 diffusers.

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 phosphorus.

Final Clarifiers

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 process.

Disinfection

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 chlorine.

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.