Final answer:
After water is removed from waste, the leftover material is called sludge. This sludge is further processed in digesters to reduce volume, eliminate odors, and destroy harmful organisms, and it may end up in landfills or be used as fertilizer.
Step-by-step explanation:
After water is removed from waste at a wastewater treatment plant, the residual material is known as sludge. This sludge, which includes both the settled solids from the sedimentation tank and the activated sludge from secondary clarifiers, is then processed further. Typically, it is placed in devices called digesters where it is held for 20-30 days. This process reduces the volume of the materials, decreases odors, and destroys potentially disease-causing organisms. Depending on its quality and composition, the digested sludge may be disposed of in a landfill or repurposed as fertilizer after thorough testing for contaminants.