City of Waukesha's Clean Water Plant

The Waukesha Clean Water Plant can be matched by just a handful of communities in Wisconsin. It treats an average of 10 to 12 million gallons a day, although it’s capable of handling an average of 18.5 million gallons a day and a peak flow of 23 million gallons a day.

It’s a big and important undertaking. Waukesha has over 260 miles of sanitary sewer pipes that carry wastewater to the plant. The pipes range from 8 to 72 inches in diameter. They’re cleaned at least yearly—more often if necessary.

preliminary treatment

Preliminary treatment begins when the wastewater arrives at the facility.

preliminary treatment

The goal is to immediately remove as much inorganic matter as possible. So the water first passes through a bar screen to remove roots, rocks and other large objects. Next, a finer screen removes rags, plastic and some forms of paper. Then smaller particles like sand, pebbles and seeds are eliminated using a grit chamber, which slows the flow, allowing grit to drop to the bottom and be removed.

primary treatment

After grit removal, primary treatment begins.

primary treatment

The water cascades like a waterfall into two wet wells to increase the water’s oxygen content, control odors and prepare it for subsequent treatment. Next the waste is processed in tanks where more solids settle to the bottom and are removed. Oil, grease and other floating materials are skimmed off. From here, the water is moved to a splitter box where it’s mixed with return activated sludge (RAS), which is wastewater that contains the microorganisms used to biodegrade organic matter. The splitter box distributes the RAS-enriched water to six aeration basins for secondary treatment.

secondary treatment

During this step of the process, the microorganisms feed on the organic waste.

secondary treatment

Oxygen is necessary for this process, so the tanks are lined with pipes that force air through diffusers, introducing small bubbles that oxygenate the water and provide agitation as they rise to the top. The microorganisms thrive in this perfect environment. They grow, multiply, and convert the waste into a brown mass called floc, which settles rapidly. At this point, carbon-based wastes and nitrogen-based compounds are removed. Next, the treated wastewater moves to final clarifiers to separate the activated sludge floc from the water. The sludge is divided in two parts. One part, the return activated sludge, is sent back to the splitter box to provide the microorganisms to treat more wastewater. The second portion is sent to a thickener as waste activated sludge.

tertiary treatment

That’s where most wastewater treatment processes end. But before Waukesha water is discharged into the river, it undergoes a third, or tertiary, treatment.

tertiary treatment

This includes phosphorus removal to prevent the growth of algae and vegetation. Sand filters remove all but the finest solids and bacteria. Any remaining bacteria or pathogens are then rendered harmless through exposure to ultraviolet light. Before discharging to the river, the water is aerated to achieve proper oxygen levels.

preliminary treatment

The goal is to immediately remove as much inorganic matter as possible. So the water first passes through a bar screen to remove roots, rocks and other large objects. Next, a finer screen removes rags, plastic and some forms of paper. Then smaller particles like sand, pebbles and seeds are eliminated using a grit chamber, which slows the flow, allowing grit to drop to the bottom and be removed.

primary treatment

The water cascades like a waterfall into two wet wells to increase the water’s oxygen content, control odors and prepare it for subsequent treatment. Next the waste is processed in tanks where more solids settle to the bottom and are removed. Oil, grease and other floating materials are skimmed off. From here, the water is moved to a splitter box where it’s mixed with return activated sludge (RAS), which is wastewater that contains the microorganisms used to biodegrade organic matter. The splitter box distributes the RAS-enriched water to six aeration basins for secondary treatment.

secondary treatment

Oxygen is necessary for this process, so the tanks are lined with pipes that force air through diffusers, introducing small bubbles that oxygenate the water and provide agitation as they rise to the top. The microorganisms thrive in this perfect environment. They grow, multiply, and convert the waste into a brown fluffy mass called floc, which settles rapidly. At this point, carbon-based wastes and nitrogen-based compounds are removed. Next, the treated wastewater moves to final clarifiers to separate the activated sludge floc from the water. The sludge is divided in two parts. One part, the return-activated sludge, is sent back to the splitter box to provide the bacteria to treat more wastewater. The second portion is sent to a thickener as waste-activated sludge. Then air is pumped into it, causing solids to float to the top, where they’re skimmed off.

tertiary treatment

This includes phosphorus removal to prevent the growth of algae and vegetation. Sand filters remove all but the finest solids and bacteria. Any remaining bacteria or pathogens are then rendered harmless through exposure to ultraviolet light. The water is now ready to flow into the river.

Wastewater treatment produces several types of solids. Biosolids (also referred to as sludge) are separated out for further processing. Other solids are sent to a licensed landfill site for disposal.

Waste-activated sludge is biodegraded, dewatered and then stored until spring or fall, when it is scattered in a thin layer over approved agricultural fields and tilled underground within six hours of application to enrich the soil.

Although the process is complex, Waukesha’s Clean Water Plant is highly efficient and successful at protecting the quality of our water resources.

Myth vs. Fact

The subject of water resource management is often emotionally charged, and the passions it raises can lead to a blurring of the line between myth and fact. We’d like to address some of the common misperceptions that have arisen since Lake Michigan was identified as the only reasonable long term water supply for Waukesha.

GET THE FACTS »

Frequently Answered Questions

Here’s the place to start…
in case you’re wondering.

FAQ »