Steps in the wastewater treatment process include screening, pumping, aerating and sludge removal. Additional steps include scum removal, killing off bacteria and processing solid waste residual materials. Wastewater that ends up in water treatment plants typically include materials such as human waste, soaps, various chemicals and food scraps. Rainwater that flows into sewers is also treated along with used water from homes and businesses.
As wastewater enters the treatment facility, it is screened to remove debris such as rocks, pieces of wood and dead animals, which are sent to a landfill. Pumping is required to move wastewater from various sources into the treatment plant, and this is done using the force of gravity. Treatment plants at higher elevations pump wastewater up into aeration tanks, while those on low ground use nearby rivers. Aeration exposes the collected raw sewage to air, which releases hydrogen sulfide, a gas that breaks down organic matter and turns it into grit.
Wastewater sludge goes into sedimentation tanks where it thickens, and debris that floats to the top is considered scum. This scum is removed by raking and it then goes through the thickening process. Some treatment plants use filtration systems during this step to get rid of a majority of bacteria and odors. Chlorine is used to destroy bacteria during the final step.