1. Welcome To Our Plant Tour

2. Wheaton Sanitary District uses biological treatment to accelerate the natural bio-degradation of sewage in a small area (the waste water treatment plant site). We provide air and sewage (the food) which enable billions of aerobic micro-organisms to thrive, and they rapidly break down the sewage. We receive many requests for tours. Tours are tailored to the interest level of the groups, ranging from local youth groups to environmental professionals. Please call (630)668-1515 to schedule a tour. Children are welcome with adult supervision. The plant is designed to treat a dry weather flow of 8.9 million gallons per day (mgd), a design maximum flow of 19.1 mgd and a peak wet weather flow of 45 mgd. The treatment provided is a biological process that includes trickling filters as roughing filters and the activated sludge process. The plant provides tertiary treatment with sand filtration. The effluent from the plant is disinfected using sodium hypochlorite (also known as bleach or chlorine) to remove pathogenic bacteria. After disinfection, the residual chlorine from the hypochlorite is removed using sulfur dioxide. Biosolids/sludge produced in the treatment process is anaerobically digested, dewatered with centrifuges, and spread on farm fields. Wheaton Sanitary District

3. PRELIMINARY TREATMENT So, what happens after you pour water down the drain? The wastewater travels inside pipes from your home, out to the street where it connects to a public sanitary sewer pipe. The public sewer in front of your house is most likely 8 inches in diameter, and, as you get closer to the plant, the lines may be as large as the 48 inches in diameter, like the one you see in the above picture. We have what's called a "biological" treatment plant. This means we create an environment, by providing food (the wastewater) and air, which encourages millions of micro-organisms to exist. These micro-organisms are the biological weapon that eats away at the waste water which makes the waste water clean enough that we can discharge it into Spring Brook Creek. Preliminary treatment consists of the following Pumping of the wastewater to a higher elevation so that it may flow through the first half of the plant by gravity, Removal of large debris with bar screens, and Grit removal.

4. Influent Pumping The preliminary treatment building, in the photo above, contains four "Archimedes type" screw pumps that lift the wastewater up from the sewers 12 feet below the ground, into the preliminary treatment building. The screw pumps are in the sloping concrete structure on the left of the building. Each screw pump is 6 feet in diameter, 40 feet long, and driven by a 100 horsepower motor with a capacity of 15 million gallons per day. Normally, only one screw pumps is in service. During wet weather periods, up to three pumps may be required. By law, the plant must be able to operate with the largest pump out of service. So, one of the screw pumps serves as a backup for emergency conditions when one of the other three screw pumps might happen to go out of service.

5. Influent Screw Pumps This photo (the screw pump is on the back of a semi truck) helps give you an idea of how large these 6 foot diameter screw pumps are. As the screw pumps turn, the vanes on the screw pumps help move the waste water up an incline to the top of the waste water treatment plant where we begin the treatment process.

6. Influent Screw Pump Motors This photos shows the 100 hp motors that turn the screw pumps from the top. These 100 hp motors drive the screw pumps through a gear reducer which reduces the speed of the motor from 1440 rpm to drive the screws at 29 rpm.

7. Bar Screens Now that the waste water has been elevated, the first step in the treatment process is to pass it through bar screens. The bar screens have iron bars spaced 3/8 inch apart. As the water flows past the bar screens, they catch large debris such as plastic bags, plastic water bottles, sticks, etc. that could damage equipment in the waste water treatment plant

8. Mechanical Rake A mechanical rake scrapes the material caught by the bar screens and lifts that material up to a screw conveyor which moves the material to a screenings washer. At the end of the screenings conveyor, we have what's called a screenings washer (with an inclined screw conveyor to promote drainage).

9. Screenings Washer Here, the screenings (removed by the bar screens) fall into the screenings washer where wash water is used to clean away any organic material from the screenings, and the dirty wash water is returned to the plant for treatment. The screenings are compressed to squeeze out water and then pushed into a garbage dumpster which is emptied about once a week by a waste hauler for disposal at a landfill.

10. Grit Removal Process Grit is material such as sand, cinders, eggshells, small rocks, and gravel which can damage pumps and other equipment in the plant. So, it makes sense to remove the grit as soon as possible. However, at this stage, organic material adhered to the grit will need to be cleaned off before the grit is removed. Air is injected from diffusers near the bottom and along a wall of the grit chamber to create a rolling motion in the tank. The mixture of air and water have a lower specific gravity than water, which allows the grit heavier than water to settle to the bottom of the tank, which slopes to a hopper (low channel in the tank) under the diffusers where the grit will be moved with an auger screw to a grit pumps that moves the grit to a grit classifier for cleaning.

11. Centrifugal Blowers Two 15 horsepower centrifugal blowers supply air to the grit tanks. Screw conveyors at the bottom of the tanks move the grit out of the tanks into hoppers. The air provides the added benefit of refreshing the waste water making the downstream aerobic treatment processes more effective. The air injected so that velocity of the roll optimizes grit settling.

12. Grit Pumps Grit pumps move grit from the hoppers and pump/push the grit to what's called a grit classifier.

13. Grit Classifier The grit classifier basically cleans the grit material (removes organic material) by washing it, much like a washing machine cleans clothes. Clean water is sprayed on the grit, the grit is agitated, and the organic material is washed off of the grit. The clean grit is moved to a garbage dumpster for pickup by a waste hauler for disposal at a landfill. The organic material reenters the treatment flow stream (in soluble form) for further treatment downstream of the grit tanks.

14. Odor Control System An odor control system removes hydrogen sulfide gas (an odor similar to the rotten egg smell you might remember from your high school chemistry class). Air is pulled out of the building from many locations, and the air is then pushed past cylindrical canisters of carbon (coated with a chemical that attracts the hydrogen sulfide molecules). Clean air is exhausted out the vertical stack on the right. As the carbon becomes saturated with the hydrogen sulfide molecules, the removal efficiency decreases. To restore the carbon's adsorptive capacity, is regenerated on a regular basis. This concludes preliminary treatment, and the wastewater is now ready for the next step in the treatment process which is called primary treatment.

15. Primary Tanks The wastewater flows from the primary tanks to an intermediate screw pump station.

16. Intermediate Screw Pump Station The intermediate screw pump station, similar to the influent screw pumps, but smaller in size. These pumps are 36 inches in diameter and only 25 feet long. They are driven by 30 horsepower motors through a gear reducer which reduces the 1440 rpm shaft speed of the motor to 29 rpm for the screws. The intermediate screw pump station is required to lift the wastewater so that it can flow through the activated sludge system by gravity.

17. Activated Sludge Process The first step we use in the activated sludge process is to provide oxygen to feed the microscopic bacteria in the wastewater by injecting streams of fine bubbles that rise through the wastewater in the aeration tanks. The bacteria feed on the organic material in the wastewater and convert it to water and carbon dioxide. This photo shows the surface of the wastewater with the bubbles rising to the top.

18. Aeration Blowers To provide the air needed, we use centrifugal blowers that can supply air at about 3,000 cubic feet per minute (cfm) at a pressure of 8 pounds per square inch (psi).

19. Secondary Tanks Wastewater leaving the aeration tanks is routed to the secondary clarifiers for further treatment. The effluent from the activated sludge tanks comes up into the center of these secondary clarifiers. The flows slowly travels out to the perimeter of the secondary clarifier tanks where the water on the surface eventually flows over weirs. As the wastewater flows outward, heavier biological mass settles to the bottom of the clarifier. At the bottom of the clarifier tank, collector arms rotate to collect the biological mass that has settled. This biological mass contains active healthy growing bacteria that developed in the aeration tanks.

20. Effluent Filtration Effluent filtration is a tertiary treatment system that removes fine suspended organic solids from the treated sewage. We use sand filters to provide tertiary treatment. The wastewater enters the tank from the trough that extends along the center of the cell, It uniformly distributes the water from the secondary clarifiers to the sand along the length of the sand filter cell. The water then flows through the sand media where it removes the fine particles. As solids accumulate on the sand, it becomes more difficult for the water to saturate through the sand, and the depth of the water over the sand increases to the point where it needs to be backwashed to remove the accumulated fine particles. When the water gets deep enough, a valve automatically stops water from coming entering the trough. At the same time, another valve allows backwash water to enter the tank from underneath the cell, reversing the flow of water for a short time period to backwash the sand filter cell.

21. Sand Filter Backwash This backwashing process carries away the fine particles (which are lighter than the sand) backwards out of the sand filter to a storage tank and then back to the plant for treatment. After sand filtration, disinfection may be required. From May 1st through October 31st, we are required to disinfect the water. See effluent disinfection to learn about the next step in the treatment process.

22. Effluent Disinfection After tertiary treatment (with sand filtration) is completed, the water is stored in a tank where it can be used in many parts of the plant for things such as filter backwashing, watering the lawn, and tank cleaning. This water is called non-potable water (NPW), and it is not suitable for human consumption.

23. Chlorine Contact Tank Water not stored for backwashing is routed to a chlorine contact tank. From May 1st through October 31st, sodium hypochlorite (bleach) is used to disinfect the water of trace levels of pathogens that might remain after treatment. To ensure this water has enough contact time with the sodium hypochlorite, the water is forced to flow through a serpentine path in the chlorine contact tank. To ensure adequate disinfection, the tank is sized so that, during peak flow conditions, the water will be in contact with the sodium hypochlorite solution for at least 30 minutes.

24. Disinfection Many treatment plants use a gaseous form of chlorine for disinfection. However, gaseous chlorine is potentially hazardous for the community. So, the District decided several years ago to use far less hazardous sodium hypochlorite for disinfection, even though it is more expensive.