Final answer:
Sewage treatment consists of primary treatment for removing large solids, secondary treatment for microbial digestion of organic material, and tertiary treatment for removing remaining contaminants from the liquid.
Step-by-step explanation:
The stages of sewage treatment correspond to different processes designed to remove contaminants and pollutants from wastewater. The primary treatment involves the removal of large solids through settling or flotation, which can be composted or sent to a landfill. In primary treatment, sewage is stored in a basin where solids (sludge) can settle to the bottom and oil and lighter substances can rise to the top. These layers are then removed and then the remaining liquid can be sent to secondary treatment.
Secondary treatment is characterized by microbial digestion of organic material, utilizing microorganisms to break down organic waste aerobically. Finally, tertiary treatment includes advanced filtration methods to remove remaining solids, microorganisms, and nutrients from the liquid part of the sewage. Collectively, these processes ensure that wastewater is adequately treated to prevent the spread of disease and protect environmental health.