RRWRD Online Plant Tour

It would not be realistic to "tour" the District's entire 1,100-plus mile collection system at this time. Tours of the Kishwaukee Street plant are tentatively planned for Spring of 2004, but until then, continue reading this page for our ONLINE TOUR. This tour will be updated in the near future to reflect changes and current information on the District's Biosolids Project.

1. Administration Building

Guests often comment on the plant's cleanliness, efficient operation, and diligent workers. Their tour begins at the Administration Building. Since original construction in 1932, this area has experienced four major remodeling phases. The building houses the District's administration offices.

2. District Laboratory

A 2001 construction project created the current laboratory facility. Today's laboratory contains modern devices such as an atomic absorption spectrophotometer and a gas chromatograph.

3. Parshall Flume

From an enclosed walkway in the Administration Building, visitors can view the incoming wastewater as it passes through the Parshall Flume. In the flume, instruments measure and record influent volume. During a typical one-hour period, over a million gallons of influent pass through the flume from collection points as far as 15 miles away. The flume is actually the second major structure the influent passes through in its reclamation sequence. Its first stop is the pumping station.

4. Raw Sewage Pumping Station

The pumping station lifts incoming wastewater high enough to allow gravity to transfer influent through the primary treatment process. A 1972 bond referendum and matching federal grants provided funding for the pumping station. This station controls wastewater flow, first to the Parshall Flume, then to primary settling tanks. Once the water reaches the primary settling tanks, individual process centers control its flow.

5. Bar Screen

The first actual treatment procedure occurs at the bar screen, located in the main pumping station. The bar screen removes coarse materials that could clog and damage pumping and treatment equipment. Cans, stones, logs and other items one inch in diameter or larger appear in screenings. The bar screen operates automatically and is self-cleaning.

6. Primary Settling Tanks

After the bar screen separates coarse materials, wastewater flows to primary settling tanks. Heavier suspended solids settle to the bottom of the tanks, while floating materials rise to the surface. Pumps transport the sediment, called primary "sludge" to thickening tanks. The remaining wastewater is now about 40% cleaner. It flows to the next process station.

7. Aeration Tanks

Aeration speeds the natural biological oxidation process, allowing operators to discharge effluent into the Rock River after only ten hours of treatment. It would take a natural stream at least five full days under ideal conditions to complete this process.

8. Aeration Control Building

The building west of the aeration tanks contains devices that control the activated sludge system's dissolved oxygen level. Operators use laboratory tests to decide on proper settings. Using a video camera and monitor, your host will show you the microbes that support the activated sludge process. (See photo at right) This building also contains the Lift Station Telemetry System that monitors 28 remote pumping stations.

9. Final Settling Tanks

After aeration, wastewater flows to a series of final settling tanks for more cleansing. The final tanks use the same method as primary tanks. By the time wastewater leaves these tanks it is 85% to 98% cleaner than it was when it arrived at the pumping station. Pressure lines move settled secondary sludge to tickening tanks described in Step 5 above.

10. Chlorine Contact Tanks

Even though the water leaving the final settling tanks looks clean and clear, it might contain microscopic bacteria. Before operators release this water into the Rock River, they place it in contact with highly controlled amounts of chlorine, for disinfection. This process occurs in the Chlorine Contact Tanks. Operators control the process, using devices in the adjacent Chlorine Control Building.

11. Final Effluent Diffuser

This structure lies across the bottom of the Rock River, just north of Bypass 20. The diffuser releases reclaimed water back into "Nature's Cycle." The underwater diffuser is 70 feet long. Its eight high-velocity discharge ports cause treatment plant effluent to mix quickly with river water. On a typical day, about 30 million gallons of water flow through our District's treatment facility. The purification cycle often takes only ten hours.

12. Grit Removal

We now return to find out what happened to the sludge after it settled to the bottom of the primary tanks. A separator removes grit (composed of small, insoluble particles such as sand and coffee grounds), allowing drivers to truck it to a landfill. Pressure lines convey the remaining sludge to thickening tanks.

13. Sludge Thickening Tanks

Gravity thickening occurs in tanks similar to primary settling tanks. Pumps feed dilute sludge (from the activated sludge process and from the primary tanks) to the gravity thickeners. The sludge settles and compacts in the thickening tanks. This process reduces sludge volume by 75%. Equipment gently stirs the sludge, helping to further separate it from the water. Pressurized pipes move thickened sludge to storage tanks, where operators control its release, for de-watering.

14. Sludge De-Watering

Centrifuges are used with municipal biosolids to either thicken or dewater . Thickening typically is done with waste activated or raw sludges to thicken solids from less than 1% to over 4%. Centrifuge dewatering of biosolids is typically used to dewater anaerobic or aerobic sludges from less than 5% to 25% or higher. Polymers are used to precondition the sludges forming a uniform floc that readily releases free water. The separation of sludge floc and water is then mechanically processed with a centrifuge to form biosolids with the texture of soil. The biosolids are then used as an organic substitute for commercial fertilizers on farm fields.

The operating principle of a centrifuge is that sludges are fed to a specially designed feed chamber where polymer and the sludges are mixed. The spinning assembly accelerates the sludges in preparation for entry into the clarification zone of the centrifuge. Rapid settling occurs in the clarification zone using centrifugal force that causes heavier solids to spin to the outside of the bowl assembly and water to be discharged over specially designed weir plates near the liquid end of the centrifuge. An inner helical screw conveyor transports the settled solids toward the solids end where additional compaction occurs and water is released. Near the solids end of the bowl the conical shape subjects solids to additional biaxial pressing where additional capillary water is released. The differential between the bowl speed and the inner helical screw conveyor speed is controlled by operators who monitor torque to optimize the residence time of the sludge in the centrifuge. High rate centrifuges typically spin at 2500 rpm or higher.

The goal is to land apply all sludge using the landfill only as a backup.

15. Maintenance Building

The last stop on our tour is the Maintenance Building. This structure lies just West of the sludge de-watering complex. It houses parts and machinery to repair and maintain the District's equipment and vehicles. The building also contains several administrative offices.