Advanced secondary treatment begins at the end the secondary settling stage. The wastewater at this point is quite clean compared to the state that it arrived in at the treatment facility. One of the last remaining concerns is the amount of ammonia in the wastewater.
Ammonia at higher levels is toxic to aquatic life and can result in harm to the environment. To remove the ammonia from the wastewater, La Porte's treatment facility involves a special type of trickling filter called a biotower. The biotowers function similar to a regular tricking filter, except that a biotower has 20 feet of media, and a regular trickling filter has about 5 feet.