Wastewater Treatment

“Using nature’s own ways to purify and recycle water”

In a sense, the natural water reclamation process is billions of years old. Nature provides the “collection system” for us by precipitation, evaporation, and ground runoff. Nature’s “treatment system” includes living organisms that purify waste material in the water of a river. These organisms settle to the bottom, and the particles are filtered from groundwater by trapping them in the rocks and sand as the water passes through.

In the last one hundred years, scientists and engineers have begun to understand some of the complex, delicate details of nature’s process. During this time, populations have grown larger and more clustered. Production methods have become more effective, but have also placed greater demands on the water cycle. In response, scientists and engineers have found ways to refine and speed up nature’s water reclamation process.

Today’s technology allows us to reclaim large volumes of wastewater (water discharged into the District’s collection system) in short time spans. The basic idea which our systems employ is “nature’s way.” Indeed, the water we use and enjoy today is actually billions of years old. Our goal, like yours, is to ensure that our community does not waste its water.

Click Here to see a video on wastewater treatment from the Water Environment Federation.



Once the wastewater is collected, the District provides treatment at its facilities located on Kishwaukee Street in Rockford. The District currently provides secondary wastewater treatment consisting of the following major treatment components:

  • Raw wastewater pumping station with Parshall Flume for recording the quantity of incoming wastewater to the treatment facility.
  • Bar screen and primary settling tanks.
  • Aeration tanks that provide for biological removal of contaminants from the wastewater.
  • Final settling tanks followed by chlorine contact tanks and the discharge of the treated wastewater to the Rock River.
  • Solids removed from the wastewater are thickened and then pumped into heated anaerobic digesters where the wastes are stabilized and methane gas is produced. Those solids will be applied to farmland as a fertilizer and soil conditioner.
  • The methane gas produced by the anaerobic digester is used as a fuel to operate a generator that produces heat for the anaerobic digester operation and electricity to operate the plant.

How The Treatment Process Works

Wastewater enters the plant and is given a preliminary screening at the headworks pumping station and bar screen (1), which removes larger debris from the water. The wastewater then goes to the Grit Removal Building (2) where sand and other heavy material is removed from the wastewater.

The total wastewater flow through the plant is measured at the Parshall Flume (3) and then is sent to the Primary Settling Tanks (4) where suspended solids are allowed to settle to the bottom of the tanks and then are removed.

Next, the partially treated wastewater goes to the Aeration Tanks (5) where pipes at the bottom of the tanks pump billions of air bubbles through the water to stimulate the growth of bacteria, which in turn remove organic materials from the water.

After aeration, the water is pumped into Final Settling Tanks (6) where any remaining solid material is allowed to settle to the bottom of the tanks and is then removed. Finally, the effluent water is sent to chlorination tanks (7) where the bacteria are killed, then the chlorine is removed at the final effluent diffuser (8) before the clean water is released into the Rock River through a series of diffuser nozzles.

Solid materials, called sludge, are removed from the wastewater and are pumped to Thickening Tanks (9) and then to anaerobic digesters (10) along with sludge from the Final Setting Tanks (6) and High Strength Waste (15). These combined sludges are broken down to produce biosolids and methane gas by the anaerobic digesters (10). The methane is used to produce electricity and hot water (14) for use throughout the plant. Biosolids from the anaerobic digesters (10) are dewatered by centrifuges (11) and then sent to storage (12) before beneficial use as fertilizer on farm fields.