Tour the Plant
The current laboratory facility was built in 2000. Lab staff performs over 60,000 analyses annually for parameters including solids, biological and chemical oxygen demand, cyanide, nitrogen compounds, anions, heavy metals, oil and grease, and volatile organic compounds. Instrumentation include UV/vis spectrophotometer, gas chromatograph mass spectrometer, inductively coupled plasma mass spectrometer, ion chromatograph, as well as various specialized proprietary equipment.
The District’s laboratory is accredited through the National Environmental Laboratory Accreditation Program.
In the flume, instruments measure and record the volume of incoming wastewater (influent). 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 third major structure the influent passes through in its reclamation sequence. Its first stop is the pumping station, and then the grit removal.
Main Pumping Station & Bar Screen
A 1972 bond referendum and matching federal grants provided funding for the pumping station. This station controls wastewater flow: first to the Grit Removal station, then to the Parshall Flume, and then to the primary settling tanks. Once the water reaches the primary settling tanks, individual process centers control its flow.
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, sticks, cleaning and disinfection wipes, and other items one inch in diameter or larger are caught in screenings. The bar screen operates automatically and is self-cleaning. The items removed from the screen are rinsed to remove organic material before the debris is hauled to the landfill.
After the main pumping station, a separator removes grit (composed of small, insoluble particles such as sand and coffee grounds), allowing drivers to truck it to a landfill.
Primary Settling Tanks
After the grit chamber removes heavier materials, wastewater flows through the parshall flume and then to the 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 and flows to the aeration tanks. The floating material is removed and pumped to the anaerobic digesters for further treatment.
Aeration speeds up 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.
Aeration Control Building
The building west of the aeration tanks contains systems 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. This building also contains the Lift Station Telemetry System that monitors 33 remote pumping stations.
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. The majority of the settled secondary sludge is pumped back to the aeration tanks as seed and the rest is pumped to a gravity belt thickener before being pumped to the digesters.
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 Disinfection Control Building.
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 projects 500 feet into the river and is 100 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.
Sludge Thickening Tanks
Gravity thickening occurs in tanks similar to primary settling tanks. Pumps feed dilute sludge 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 thicken it and guide it towards the sump where it is then pumped to the anaerobic digesters.
Waste activated sludge from the aeration basins is thickened using a gravity belt thickener. Polymer is added to cause the smaller sludge particles to form larger particles. The sludge is fed to the filter belt. The solids are collected on the belt as the water drains through the porous filter belt. The thickened sludge is then collected and pumped to the anaerobic digesters.
The digesters use Anaerobic bacteria to stabilize and reduce the volume of the bio-solids (sludge). The Anaerobic bacteria must remain in an oxygen-free environment and are kept at 100 degrees Fahrenheit at all times. This process converts the volatile portion of the bio-solids to biogas. The biogas, primarily methane, is used to heat the digesters and used as fuel for the District’s Energy Production (cogeneration) process. Excess biogas is stored for later use.
Centrifuges are used with municipal bio-solids to either thicken or de-water. At the District, they are used to de-water the digested sludge from less than 5% to 20% or higher. Polymers are used to precondition the sludge 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 bio-solids with the texture of soil. The bio-solids are then used as an organic substitute for commercial fertilizers on farm fields.
The operating principle of a centrifuge is that sludge is fed to a specially designed feed chamber where polymer and the sludge are mixed. The spinning assembly accelerates the sludge 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 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 2,500 rpm or higher.
Bio-Solids Storage Building
The District stores its dewatered bio-solids (sludge) in the 200 x 300 foot Bio-solids Storage Building. This building has the capacity to store approximately six months’ production of bio-solids or 9,000 wet tons. The District’s goal is apply these bio-solids to area farmland as fertilizer and not to put it in landfills.
High-Strength Waste Receiving Facility
The District accepts high strength waste from food processors. When this waste is fed into our digesters along with treatment plant solids, we produce enough electricity to meet 90% of our energy requirements.
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 is the main receiving location for deliveries and also contains several administrative offices.
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