bacteria in septic systems
There are many different types of bacteria that occur naturally in a septic system. Those present in the septic tank help to process waste and organic matter. This is the first stage of waste treatment. Liquid that has been partially treated in the tank is called effluent. Effluent entering the drain field is then treated while passing through the biomat.
The biomat is a naturally occurring tar-like substance that forms on the bottoms and sides of the drain field trenches. It is made up of living anaerobic (existing without oxygen) bacteria, which feed on organic matter in the effluent. As the biomat matures it grows thicker, slowing down the flow of effluent to the surrounding soil. As the effluent passes through the biomat pathogenic organisms and viruses are removed. On the outside of the trench, beyond the biomat where the soil is not saturated, are living colonies of aerobic (existing with oxygen) bacteria. These aerobic bacteria colonies feed on the excess biomat as it matures, they keep it from becoming so thick that wastewater will no longer pass through.
When soil floods aerobic bacteria colonies will die off and no longer keep the biomat in check. The biomat will grow too thick and drainage will stop. Further, as these colonies die off they leave behind sulfides, which over time will clog soil passages stopping the flow of water.