Isolation and Identification of Anaerobic
and Facultative Bacteria Present in the
Digestion Process
N. C. BURBANK, JR., Professor of Civil and Sanitary Engineering
JOHN T. COOKSON, Graduate Student
JOSEPH GOEPPNER, Graduate Student
DAVID BROOMAN, Graduate Student
Environmental and Sanitary Engineering
Washington University
St. Louis, Missouri
INTRODUCTION
The digestion process produced by the fermentative action of anaerobic and
facultative bacteria has long been useful to humankind. There are many present
day applications in the chemical process industries and many of interest to sanitary engineers in the treatment of waste, particularly sewage sludge digestion and
stabilization of meat packing plant waste.
The environmental conditions which prevail in the sludge digestion process
sustain the facultative and strict anaerobic bacteria most effectively. The flora
reported in sewage sludge digesters consists of two main groups of bacteria, the
saprophytic acid formers and the methane formers. The saprophytic bacteria are
naturally abundant in sewage and can reproduce rapidly in the digestion process.
These bacteria are recorded as producing the volatile acids which can occur in
large quantities in anaerobic digesters (1,2).
The second group of bacteria, the methane formers, have been reported as
responsible for the utilization of the end products of the acid forming bacteria.
These two groups of bacteria live in symbiosis in the same environment. The
methane organisms ferment only very select substrates. They do not ferment
carbohydrates and amino acids as the common saprophytic bacteria (3,4). The
methane forming bacteria are strict anaerobes and their population in sewage is
reported to be small. Methane gas is one of the end products formed by these
organisms. At present only ten methane organisms have been cultivated and
identified. Only six of these have been isolated in pure culture. The ten identified organisms are listed below (3).
Methane-bacterium omelianskii
Methanobacterium propionicum
Methane-bacterium formicicum
Methanococcus      vannielU
Methanococcus      barkii
Methanobacterium suboxydans
Methanobacterium sobngenica
Methanococcus      mazei
Methanobacterium rummantium
Methanosarcina      methanica
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