Water Reclamation Process
Walworth County Metropolitan Sewerage District (WalCoMet) serves an area encompassing approximately 70 square miles of Walworth County and a population of approximately 28,000 residents.
Every hour of every day, wastewater from homes, schools, businesses, and factories from our service area enter the water reclamation plant through 3 main interceptor lines. At the District, we use a combination of physical and biological processes to remove contaminants and clean the wastewater before releasing it back into the environment.
Prior to treatment, the flow is sampled and measured for biological oxygen demand (BOD), suspended solids, ammonia, phosphorus, and pH. These measurements determine the amount of pollution in the waste stream.
Wastewater travels through our collection system and enters the plant at our headworks facility located south of Highway 11 in the City of Delavan.
Preliminary Treatment
Wastewater, also known as influent, travels through our collection system and enters the plant at our headworks facility. After entering the facility, the influent flows into the screening building where large debris such as wipes, paper towels, feminine hygiene products, dental floss, sticks, and rocks are removed. The debris is washed, compacted, and then bagged for disposal. This compacted waste is hauled to a licensed solid waste facility (landfill) for disposal. After the initial screening, the influent enters the pista grit, where heavier materials such as coffee grounds, sand, and material from household garbage disposals are removed. Grit is pumped from the bottom of the pista grit to the grit washer. Clean grit is then pumped into a dumpster and hauled to a licensed landfill for disposal.
Flow Measurement
As flow leaves the pista grit, it enters a parshall flume where flow is measurement. After the parshall flume, the flow is split into four different drop boxes that feed the individual primary clarifiers.
Primary Treatment
In the primary clarifiers, the velocity is reduced so approximately 65% of the suspended solids (primary sludge) settle to the bottom where it is collected and pumped to the digester for further treatment. By removing a large volume of solids, it reduces the amount of BOD and phosphorus in the waste stream. In addition, floatables such as oils and grease are skimmed from the top of the primary clarifiers, collected, and hauled to a licensed landfill for disposal. After 3-4 hours of detention time, the partially treated water, now called primary effluent, exits the primary clarifiers through weirs at the end of the tank. Wastewater then flows to the lower plant for further treatment.
Odorous Air Treatment
All odorous air from the preliminary and primary treatment processes is captured and discharged into a biofilter containing a specialized mix of porous kiln dried rock and wood chips. Microorganisms in the biofilter feed on the odorous compounds neutralizing them to salts, carbon dioxide, and water.
Secondary Treatment – Activated Sludge
Wastewater from the primary clarifiers enters a splitter box where the flow is split evenly between three aeration tanks where biological treatment begins. The wastewater is treated by microorganisms that use the pollutants in the water, like ammonia, BOD, and phosphorus as a food source. In order to use the pollutants as a food source, the microorganisms need oxygen, which is provided through air diffusers at the bottom of the tank. As the microorganisms consume the pollutants, they grow and reproduce, therefore producing more microorganisms, carbon dioxide, and water. As the wastewater exits the aeration basin, it enters the secondary clarifier. In the secondary clarifier, the microorganisms settle to the bottom and clean water flows over the weirs. The microorganisms are removed from the bottom of the clarifier and are returned to the splitter box to be mixed with the entering primary influent to start the whole process over again. The clear water that flows over the weirs is then pumped to tertiary (advanced) treatment.
Waste Activated Sludge Thickening
A small percentage of microorganisms removed from the secondary clarifier are wasted to a holding tank where they are stored temporarily. From the holding tank, these microorganisms are pumped to a rotary drum thickener and mixed with polymer. The polymer conditions the biosolids to increase the separation of water from the microorganism. Following the addition of polymer, the waste activated sludge is sent to the digester for further processing.
Tertiary Treatment – Sand Filtration
The tertiary treatment process consists of six sand filters that remove any remaining solids. Solids collected on the sand filter are washed off in a backwash cycle and send back to the aeration basins for further treatment. The water is then sent to disinfection, where any viruses or bacteria that have survived the treatment process are killed using UV light. After disinfection, the water enters the post aeration where it is saturated with dissolved oxygen prior to discharge into the receiving stream. The dissolved oxygen saturation is important so there is enough oxygen available to aquatic life in the stream. At this point in the reclamation process, 99.99% of all pollutants have been removed from the treated wastewater and is called effluent.
Anaerobic Digestion
All solids removed in previous processes are pumped into large, heated tanks which are maintained at 98.6 °F (human body temperature) under anaerobic conditions. The sludge is heated to break down any disease-causing organisms, use it as fertilizer, and create methane gas. The methane gas produced by the digesters is re-used to heat the digesters.
Land Application of Biosolids
Once the anerobic digestion process is complete, the solids, now called biosolids, can be used as a fertilizer and soil conditioner on agriculture fields. Land application of biosolids occur in springtime before crops are planted, and in fall when the crops are removed from fields. Each year, approximately 3 million gallons of biosolids are applied to area agricultural fields. Biosolids are injected into the soil at a depth of 4-9 inches, ensuring better incorporation of the nutrients.
Laboratory
The laboratory is an essential part of the day-to-day operations in the reclamation facility. Adjustments to various processes are made based on daily or weekly lab results. The lab technician conducts a series of tests in accordance with the National Pollution Discharge Elimination System (NPDES) permit. Facility sampling is conducted daily, and lift stations are sampled and analyzed monthly.
Control Room
The treatment plant processes are monitored and controlled by a computer-based instrumentation and control system. In the control room, operations staff can check the status of the plants’ operating systems, adjust equipment, monitor flow volumes, and monitor lift stations. The control room provides operations staff with monitoring capabilities 24 hours per day, 7 days per week.