Humans generate and pass large quantities of fecal coliform, including E. coli, along with organic material into a septic system. Apparently, human intestines are swarming with huge numbers (millions? billions?) of these organisms. They supposedly help humans absorb vitamin K (any verification of this statement from readers would be appreciated). It is very important for the septic system to reduce the numbers of coliform bacteria within the septic tank to ensure groundwater is not contaminated.

Fecal coliform bacteria require nutrients and a relatively warm and stable temperature to live. Remember from the first blog on this topic that these bacteria are facultative anaerobic; they can live with and without oxygen!

Anaerobic and aerobic septic tanks reduce the number of fecal coliform bacteria by:

  • Allowing the organic waste to settle at the bottom of the septic tank where it will be removed by pumping.
  • Allowing bacteria to consume nutrients, breaking down organic material into gases.

Note that aerobic bacterial respiration is vastly more efficient than anaerobic bacterial respiration at consuming nutrients and breaking down organic waste. As a result, the wastewater leaving the aerobic septic tank (the effluent) will be significantly cleaner (containing less nutrients) than the anaerobic septic tank’s. As a result, the aerobic effluent is not suited to support as many coliform bacteria as the anaerobic effluent. The Total Fecal Coliform Count for an aerobic septic tank will be much less than an anaerobic septic tank.

When a sample of wastewater is taken from a septic tank for fecal coliform analysis at a certified laboratory, the laboratory will conduct a test for the presence of E. coli, which is an indicator of the presence of fecal coliform bacteria, in general. E. coli is easily detectable, abundant and not readily found except in feces (for more information, read the FDA’s Bacteriological Analytical Manual, Chapter 4,

The results of the test is a derived number representing a Total Fecal Coliform Count. This number will usually be classified in units of colony forming units per gram or milliliter (cfu/g or cfu/ml). A colony forming unit is analogous to one bacterium. The readings for raw sewage can be in the thousands of cfu/ml.

As hard as it is to believe, levels of acceptable Total Fecal Coliform Count for a septic system are rarely defined by health departments! This is probably due to the fact that Total Fecal Coliform Counts can be correlated with the BOD5 and TSS measurements. This is logical because the bacteria have to have nutrients to survive and BOD5 and TSS are indicators of the amount of nutrients present in the wastewater.

We have documented incoming wastewater to a septic tank as high as 5,000 cfu/ml. With an installation of an Aero-Stream Remediator in the septic tank, the exiting wastewater (effluent) had a Total Coliform Count of 190 cfu/ml, a 96% reduction! So, to keep the Total Fecal Coliform Count low in your septic system, convert to an aerobic septic tank environment and keep the groundwater clean.