When continuous, a portion of the wastewater is recirculated back to the distribution system. Sewage first goes to a settling tank where much of the solid matter settles out of the wastewater. The wastewater is then pumped to the distributor, which sprays it onto the surface of the media. The media act as a substrate to which microorganisms attach themselves. Empty space between the media allows for the presence of air, creating an aerobic environment for the microorganisms.
Plastic media have significantly more empty space, thus allowing for a greater oxygen transfer.
As the wastewater passes over the media, these microbes feed upon organic material. The microbe population eventually grows to form a layer of slime over the media. Portions of this slime are sloughed off each time wastewater passes through the filter. After it has been collected in an underdrain beneath the filter, the wastewater is then sent to a second settling tank where slime debris is allowed to settle out. Trickling filters are good at removing nitrogen and organic matter from the wastewater.