View this video to see the difference between extended aeration and fixed film systems.

In extended aeration systems microorganisms that break down the wastes are free floating and suspended (or floating) in the wastewater. This system is shown in the video and is the system on the left. Notice how brown and dense the water looks.

In fixed film systems, the microorgansims that break down the wastes are attached to a media. This system is shown in the video and is the system on the right. Notice how clear the water is.

In extended aeration systems, a “flushing” of the contents in the aeration chamber during peak or high flow periods, such as on laundry day, occurs. Where drip disposal is utilized, the brown water moves out of the unit and into the dose tank where it will cause clogging of the filter in the headworks. This results in more frequent and higher maintenance costs. Where the unit is followed by a conventional drainfield, the brown water moves out of the unit directly into the drainfield where it will cause the soils to “plug up” over time resulting in drainfield failure.

In fixed film systems, this “flushing” of contents does not occur because the microorgansims are attached to the media. Filters don’t get clogged and drainfields don’t have “stuff” moving into them that shouldn’t be there!