Wastewater contains particulates and pollutants which can be removed by filtering processes. Most all septic treatment systems use some form of filtration. These processes often involve providing a large as possible surface area for bacteria to grow. The bacteria are then used as the ionic filtration units.
The septic filtration media can be synthetic (plastics, or woven fibers) or natural like gravel or sand.
There are a few septic products on the market which use filtration as the primary means of treatment