The Trickling Filter at a Sewage Treatment Plant Works by

The trickling filter at a sewage treatment plant works by

A) passing wastewater through fine sand and then mechanically removing fine pollution particles.
B) passing wastewater through a thick bed of rocks that contains chemicals that sterilize the water and neutralize chemical pollutants.
C) passing wastewater through a thick bed of rocks where biofilms of bacteria and fungi on the rocks remove much of the organic material dissolved in the wastewater.
D) adding fertilizer to wastewater and then passing it through a culture medium that is rich in oil-eating prokaryotes.