Aeration systems use aerobic bacteria to purify grey water. The process is generally similar to a grey water treatment tank in its initial stages. Solids and grease are removed in the first chamber. The effluent is then forced into a second chamber through a pipe equipped with a filter or baffle. Next, the effluent is aerated with fine bubbles of air, facilitating the growth of aerobic bacteria, which feed on and decompose the organic nutrients. When decomposition is complete, the partially treated effluent flows into a settling chamber. Bacteria settle to the bottom of the chamber, where a sloping floor returns them to the first chamber to continue biodegradation. Aeration systems require electricity to diffuse the air bubbles into the tank. As well, aeration systems also require more maintenance than a simple grey water treatment tank. Therefore, this option should only be considered only where appropriate power can be generated and a custodian is on-site.