Septic Systems: Total Fecal Coliform – I

Another measurement used to judge how effective septic systems are treating wastewater is the Total Fecal Coliform Count measurement.

In prior blogs, the BOD5 and TSS measurements were discussed in some detail. These two measurements are often used to judge how well a septic tank and drainfield are performing. Health departments have long documented anaerobic septic system performance with regards to BOD5 and TSS levels and have, subsequently, developed thresholds that anaerobic septic systems should perform to.

Total Fecal Coliform Count, however, is also a very important indicator of how well a septic system is processing wastewater and removing potentially harmful bacteria. But, what are coliforms and fecal coliforms?  Where do they live and are they all harmful?

Depending on who is defining the term, coliform either refers to the test for coliform bacteria or most, if not all, of the family of bacteria called enterobacteriaceae (Note: the FDA’s Bacteriological Analytical Manual, Chapter 4,, contains an excellent discussion of how the coliform name was applied to this family).  This and subsequent blogs will use the coliform term to represent the bacterial family.

There are many species of bacteria in the coliform family. One common and interesting characteristic of these bacteria is that they can live with and without the presence oxygen! This biological feature is known as being facultative anaerobic. These bacteria are extremely versatile and robust because of this ability to switch their respiration processes in the presence or absence of oxygen. (Note: Wikipedia entries for Enterobacteriaceae and Coliform bacteria and other referenced pages and links contain detailed technical information about how these bacteria live and what their common characteristics are).

A subset of the coliform family are the bacteria known as fecal coliform. In contrast to the larger group of coliform bacteria that can be found throughout the environment, fecal coliform bacteria are mostly found living and thriving within the feces and intestines of animals and humans, hence the name fecal coliform (Note: the FDA’s Bacteriological Analytical Manual, Chapter 4, also has an excellent technical description of how the term fecal coliform came to designate this group of bacteria).

Within the fecal coliform group of bacteria, the greatly feared bacteria called E. coli can be found.  According to the FDA and almost all state health departments (for example, Washington State’s Department of Health at, E. coli, particularly the O157 strain or mutation, is very harmful to humans when ingested. This strain does not naturally occur in humans; it found in livestock. According to many sources, the other strains of E. coli and fecal coliforms are not as dangerous as the O157 strain, although there is debate about this online.

There are a lot of strains of the E. coli bacteria. It and the other bacteria in this family are constantly mutating and laboratories have only recently become capable of identifying and testing for these strains. In fact, another strain called O104 looks to be the cause of widespread sickness in Europe earlier this year (see the FDA Press Release at

Next: the Total Fecal Coliform Test and what the results mean.


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