Mysteries Explained: What happens when I flush the toilet?

A. Plant Influent: Waste enters the treatment facility through the municipal sewer system.

B. Coarse Bar Screen: Metal bars collect large debris such as rags, wood, plastics, etc.

C. Grit Removal: The wastewater flows through a channel, allowing dense, inorganic material to settle on the bottom. Scrapers, hoppers and clam buckets remove the collected grits.

D. Primary Settling: The wastewater flows into large settling tanks which allow suspended solids and organic material to sink to the bottom of these tank. The raw sludge that settles to the bottom of these tanks is removed through hoppers and sent to a sludge thickener.

E. Partially treated wastewater is drawn from the top of the settling tanks.

F. Aeration: The large Trickling Filter mixes the partially treated wastewater with oxygen to support bacteria which devour organic waste. The bacteria levels are managed to provide the most efficient removal process.

G. Final Settling: The cleanest wastewater is drawn from the top of the final settling tanks through spillways. By this point the water is already quite clear. Once again, suspended particles settle to the bottom and are removed by scrapers or hoppers.

H. Plant Discharge: The cleanest water is drawn from the surface.

I. The treated water is tested to ensure it meets the Missouri Department of Natural Resources standards and is returned to the Mississippi River.

J. Sludge Thickening: Sludge from the primary settling tanks and final settling tanks is drawn from the bottom of the tanks and pumped to the sludge thickener. From the sludge thickener it is pumped into a contact stabilization tank where lime is added to kill off pathogenic bacteria to a certain level.

K. , L. and M. Fertilization: The concentrated sludge, or bio-solids are sub-surface injected onto farmland for fertilizer.