Meanwhile, the heavy stuff, called sludge, is baked. Heating sludge kills harmful bacteria and also breaks it down into water, carbon dioxide and methane gas. The methane gas is recycled, and used to power the plant. After you flush, it doesn't just go away. Here's where it goes.
All wastewater enters the treatment plant through the same pipe.
Wastewater passes through bar screens to remove large pieces of garbage, like rags and sticks. The garbage is taken to a landfill. Then, water is pumped to settling tanks where solids sink to the bottom and are removed. Solids that float are skimmed away. This is called Primary Treatment .