The ultraviolet (UV) disinfection process is provided to disinfect the main wastewater treatment plant (WWTP) final effluent. Effluent is disinfected to reduce the number and viability of microorganisms discharge. As a result of this reduction, the number of disease-causing organisms is reduced, minimizing potential health risks in the receiving stream. Disinfection is required year-round at the Superior WWTP; always refer to the latest Wisconsin Pollutant Discharge Elimination System (WPDES) permit for current requirements.
The UV disinfection process disinfects the wastewater by inactivating microorganisms with UV energy. The physical process relies on the discharge of electromagnetic energy from a source (lamp) and absorption by an organism’s cellular material (specifically the cells’ genetic material). The electromagnetic energy disrupts the cells’ genetic material, preventing replication of the microorganism. This system was intalled in 2012.
Anaerobic digestion stabilizes the solids removed from the primary tanks and final clarifiers. About 15,000 gallons of sludge are pumped daily to two anaerobic digesters. Inside the digester, the sludge is heated to 125° F or above for 10 to 14 days. Conditions in the digester are anaerobic (no oxygen present). Under these conditions anaerobic bacteria thrive. They consume organic molecules and produce methane gas and carbon dioxide. The methane gas that is produced is used to heat the sludge in the digesters creating a self-sufficient process. After digestion is complete, the sludge is sent to the belt filter press to remove water before disposal. Each digester has a volume of 500,000 gallons.
Belt Filter Press
When the sludge comes out of the anaerobic digester it is about 95% water. The Belt Filter Press is the tool we use to press out as much of the water as possible. After running through the press, however, the sludge is still 75 to 80% water. The sludge is sent to a landfill for disposal. By mixing our sludge with solid waste, the rate of biodegradation in the landfill is enhanced. The City produces 1500 - 2000 tons of wet sludge per year.