The filtering process has 6 steps. They are
The water treatment process is complete. It delivers three useful products; clean water, biosolids, and biogas.
- The process begins by screening out large objects such as rags and sticks. Sand, gravel, and grit settle and are taken to a landfill. Wastewater flows into concrete channels, where it is stirred by large paddles and injected with pure oxygen. Inside oxygen-loving, aerobatic bacteria digest the waste that would otherwise pollute the river.
- The wastewater flows into domed clarifier tanks where the sticky clumps of bacteria settle out as sludge. Most of the sludge is returned to the channels to provide an ample supply of microorganisms for the treatment process. Remaining sludge is removed and treated further to make a fertilizer product.
- The water is then filtered through several layers of sand, gravel and coal to trap bits of solid material. Sometimes, the water is disinfected with a strong bleach solution.
- The water cleaning process takes around 10 hours. The water is then returned to the St. Louis River or Lake Superior.
- The sludge continues through the treatment system. It is piped to tanks called digesters. Within these tanks anaerobic bacteria thrive without oxygen, breaking down sludge, digesting it and reducing its volume and mass. High temperatures are also used to kill pathogens, Microorganisms that can cause disease.
- The bacteria produce methane-rich biogas as they digest waste. WLSSD captures the methane and burns it to heat the digesters and generate electricity used in the treatment plant. After about 30 days, the sludge is taken out of the digesters and spun in centrifuges to remove water. The final product looks and feels like damp soil. This nutrient-rich fertilizer is called Field Green biosolids. ( Field Green biosolids are spread on farm fields and mine reclamation projects as a valuable fertilizer and a soil amendment.)
The water treatment process is complete. It delivers three useful products; clean water, biosolids, and biogas.