Sewage Treatment

The goal The major goal of wastewater treatment is to prevent bacteria and viruses in human waste from infecting the public. Sewage also contains undesirable materials. Think about what goes into toilets & storm drains. Are they both going to the same place?

Sewage treatment Post-use cleaning of municipal water occurs at a sewage treatment plant. Ideally all undesirable materials that enters our sewage should be removed before “used” water is returned to rivers and streams.

Six step process Screening and grit removal Primary settling Aeration Final settling Disinfection PH adjustment & removal of ions

Screening and grit removal

Screening and grit removal

Primary Settling Floating grease and scum are skimmed off and solids are allowed to settle as sludge.

Settling tank

Close up of a settling tank

Aeration Air circulation and exposure to aerobic bacteria digest complex substances

Final settling More sludge settles out. Most sludge is aerated, chlorinated, dried, and sent to a landfill.

Disinfection Chlorine added to kill germs

Iron ion removal

Iron ion removal

Prior to discharge into the reservoir

Sludge Gas Gas is produced during sludge aeration and digestion. This slug gas usually contains about 65% methane and 25% carbon dioxide. Methane is a good fuel Natural gas supply