The Trickling Filter at a Sewage Treatment Plant Works by

The trickling filter at a sewage treatment plant works by

A) passing wastewater through a thick bed of rocks.Biofilms of bacteria and fungi on the rocks remove much of the organic material dissolved in the wastewater.
B) adding fertilizer to wastewater and passing it through a culture medium rich in oil- eating prokaryotes.
C) passing wastewater through fine sand,mechanically removing fine pollution particles.
D) passing wastewater through a thick bed of rocks that contain chemicals that sterilize the water and neutralize chemical pollutants or bind with them to produce a harmless precipitate.