Final answer:
Tertiary treatment is the final stage of the water treatment process, where additional filtration and disinfection are conducted to remove remaining contaminants and pathogens.
Step-by-step explanation:
Tertiary treatment is the final stage of the water treatment process, used to further clean water before it is discharged into a sensitive ecosystem. During this stage, the water undergoes additional filtration and disinfection to remove any remaining contaminants and pathogens. For example, sand filtration and enhanced biological phosphorus removal are methods used in tertiary treatment to remove particulate matter and reduce nutrient levels, respectively.