Wastewater Utility Frequently Asked Questions


Where does the water go? 

Water returns to the environment via the Wastewater Treatment Plant on Tripp Road, which provides treatment and sanitary disposal of Janesville's sewage.  It takes approximately 6-18 hours for the liquid and approximately 20 days for the solids to pass through the sewage treatment plant.  The flow through this facility averages 13 million gallons per day.  The plant can treat flows up to 19.8 million gallons per day removing harmful elements of the wastewater through various processes before the water is sent to the Rock River.  Solids are dewatered with centrifuges and applied to approved farmland.

How does the sewage treatment process work? 

Gravity helps sewage flow through the mains to the treatment plant. When sewage first reaches the treatment plant, the influent spiral lift pumps raise the sewage to the elevation of the treatment plant. Then it passes through a bar screen which catches large objects and empties into grit tanks. Huge blowers aerate the liquid in these tanks. Scrapers and chain and bucket collectors remove the grit (sand) which settles to the bottom of these tanks.

Next, it is on to the primary clarifiers. The flow is slowed in these tanks to allow the sludge to settle to the bottom. Then a chain and flight system, similar to the apron in the bottom of a manure spreader, pushes the sludge to one end to be pumped to the anaerobic digesters. The anaerobic digester allows bacteria to break down the sludge in a closed container without oxygen. The aeration tanks, which are where the liquids from the primary clarifiers go next, allows the bacteria to break down the sewage in an oxygen environment. Liquid flowing out of the aeration tanks goes to the three final clarifiers. The liquid and solids are separated in these tanks with the liquid going on to the disinfecting tanks, while the solids are returned to the aeration tanks to be processed again. Liquid leaving the chlorine contact tanks cascades over steps to introduce air back into the water right before it enters the Rock River.

How does the wastewater get from my house to the treatment plant?

The Wastewater Utility maintains a sewer collection system 300 miles in length that collects and conveys sewage to the treatment facility (long enough to reach from Janesville to St. Paul, Minnesota). The City operates ten small lift stations to help the sewage on its way from low points within Janesville. Since we installed much of the sanitary sewer system more than 50 years ago, the Utility has a program to televise older or problem sanitary sewers. This allows the Utility to see inside the sewer pipe and check its condition to ensure reliable service. The Utility annually televises approximately 9 miles of pipe.

Can I be hooked up to public sewer?

The answer depends on many variables including the property's location and whether it is in city limits, street planning, timing, and other issues. Sewer and water service will involve a special assessment to the property served in proportion to the public street frontage in all cases. Contacting the Engineering Division at 755-3160 to discuss the specific circumstances of your location is recommended.

Whom do I call if I have a wastewater-related question?

For service and maintenance, call 755-3115 between 7:00 a.m. and 4:00 p.m. The Wastewater Utility provides emergency maintenance service to reduce inconveniences caused by water main breaks, water service leaks, sewer backups, or other emergencies. If these problems occur during non-working hours (after 4:00 p.m. Monday through Friday and on weekends), residents may reach the emergency maintenance crews by calling 755-6375.  Questions regarding water and wastewater bills should be referred to the Utility Billing/Municipal Billing staff located in the City Clerk's office at 755-3090 between 7:30 a.m. and 4:30 p.m. Monday through Friday.

Where does the wastewater come from?

The wastewater is transported from all the residential, business and industrial customers by the collection system (sewer pipes).

How does the Wastewater Treatment Plant process the wastewater?

The wastewater is pumped from a wet well located at the end of the collection system to the pretreatment process. This process removes the items that may cause maintenance problems throughout the entire treatment process. From the pretreatment process, the wastewater travels to the primary clarifiers where the settable solids (primary sludge) and floatable material (skimmings) are removed and pumped to additional processes: sludge (bio-solids) digestion and skimmings removal. The sludge is pumped into a primary digester where the bio-solids are heated to a temperature of 98 Fahrenheit.  The temperatures in both digesters are monitored and maintained at constant levels to support both their growth and life functions. While the bacteria break down the organic materials, several gases are generated, one of which is methane. The methane gas is stored in digester #3 which has a floating gas cover. The methane gas stored in this digester is utilized in our microturbines to generate electricity and produce hot water, both of which are used to reduce energy costs at the plant. The bio-solids are then processed for disposal by centrifuging. The centrifuges produce a dry cake of 19% to 22% dry solids. This material can be disposed of by  land application to approved farm fields.  This program utilizes area farms for bio-solids disposal and is a good soil conditioner. Secondary treatment is the process that follows the primary settling. The secondary treatment can be separated into four processes: biological phosphorus removal, activated sludge, final clarification and disinfection. The first process that follows the primary settling process is called biological phosphorus removal (BPR). The BPR process is used to promote an environment essential to the growth of phosphorus accumulating organisms that are utilized in the BPR process. The second part of secondary treatment is called activated sludge. The activated sludge portion of treatment consists of three aeration basins where the flow proceeds. The activated sludge portion utilizes fine-air diffusion to support the air requirement that the microorganisms need to maintain their life functions in an aerobic environment. Theses microorganisms form a bio-mass called a floc. The floc consists of thousands of microorganisms which change the specific gravity of the dissolved solids and assist in their ability to settle. The wastewater and the floc are called mixed liquor. The mixed liquor flows from the aeration basins to the final clarifiers. The bio-mass in the mixed liquor is settled out in the final clarifier and the clear liquid proceeds to the chlorine contact tanks.The last step, is treatment of the water with ultra violet light which disinfects the water for bacteria. The water is then discharged to the Rock River.

Does the Wastewater Treatment Plant monitor its final effluent?

Yes. There are several automatic samplers in specific locations that collect samples for analysis. These samples are analyzed and recorded daily for both plant control and reporting purposes. Each month the Wastewater Treatment Plant submits a Discharge Monitoring Report (DMR) to the Department of Natural Resources.

Can you arrange a tour of the Wastewater Treatment Plant?

The Wastewater Utility Plant staff provides tours of the treatment processes and laboratory procedures to students; professional organizations and interested groups. Plant tours are available and can be arrange by calling 755-3120 during normal business hours (Monday - Friday 7:00 AM - 3:30 PM).