Aeration systems are "cousins" to septic tanks, they use bacteria that live only in the presence of air. The purification process in an aeration system is generally similar to a septic tank in its initial stages. Following treatment in the first chamber, incoming waste water forces effluent into a second chamber, through a pipe equipped with a filter or baffle. Next, fine bubbles of air are blown into the effluent, encouraging the growth of aerobic bacteria which feed on the organic nutrients and decompose them. The partially treated effluent then flows into a settling chamber. Bacteria fall to the bottom of the chamber, where a sloping floor returns them to the first chamber to continue bio-degradation.