1) PRELIMINARY TREATMENT (HEADWORKS) Mechanical screening removes large debris and rags from raw wastewater. Grit removal separates sand and gravel.
2) PUMPING Wastewater collection systems rely on the force of gravity and lift stations to move sewage through the plant. Wastewater often has to be pumped to a plant’s highest process elevation (Main Lift Station).
3) AERATING Decaying organic matter uses up oxygen. Aeration replenishes it. Return Activated Sludge is pumped to front of the aerators to aid the biological process.
4) REMOVING SLUDGE Sedimentation tanks allow the heavy sludge to settle to the bottom and be pumped out. Dewatering allows thickening of the sludge prior to processing in large digester tanks.
5) REMOVING SCUM Lighter materials such as grease, plastics and soap form “scum”; slow-moving rakes skim it off the surface. Scum is thickened and pumped to the digesters along with the sludge.
6) DISINFECTION: KILLING BACTERIA At the end of treatment, chlorine is added to kill bacteria. Most chlorine is eliminated as bacteria are destroyed. The treated water (called effluent) is then discharged to a local river, lake or the ocean.
R) TREATING RESIDUALS Solid-waste materials are kept for 20 to 30 days in large tanks called digesters where bacteria breakdown, reducing its volume and odors. The finished product, free of organisms that can cause disease, is sent to landfills or used as fertilizer.