The Biochemistry of Methane
Fermentation  Using Cj4 Tracers
JOHN S. JERIS, Research Assistant
Massachusetts Institute of Technology
Cambridge, Massachusetts
and
PERRY L. McCARTY, Associate Professor of Civil Engineering
Stanford University
Stanford, California
In spite of the many years of operation of the anaerobic digestion process,
it is still one of the most complex and sensitive biological methods used in
waste water treatment. Digestion normally presents the most difficulty in the
operation of treatment plants, yet research on the process has been lacking.
Fundamentally, the major problem amounts to a lack in understanding the
biological factors which control digestion. Once the microbiology and hio-
chemistry of the process is completely understood, digestion of organic sludges
should become more economical and less troublesome.
Sewage sludge is so heterogeneous that its individual constituents must be
studied separately in order to obtain comprehensible results. Fats, carbohydrates, and proteins make up the bulk of sewage sludges, and are likely
groups of compounds for research studies. In this investigation representative
compounds from these three groups were used. These compounds are degraded initially to organic acids and short chained organic compounds. Further utilization is limited to the unique methane forming organisms which
have the ability to use carbon dioxide as a hydrogen acceptor and ferment
acetic acid. Because of this limitation, it was felt that even with mixed cultures the biochemistry could be studied by using C^4 ttacers, and the results
obtained should compare favorably with pure culture work.
The knowledge ofthe fundamental biochemistry involved in this anaerobic
process is important if digestion is to be used to the maximum possible efficiency. Proper operation of any process is related to the understanding of the
fundamentals. The purpose of this work then, was to study the fermentation
of the fatty acids, carbohydrates and proteins in order to determine: (1) general degradative mechanisms, and (2) the importance of acetic acid as an intermediate.
PREVIOUS WORK
In the early studies of the methane fermentation of acetic acid, considerable controversy arose concerning its degradative mechanism. Buswell (1)
believed that the degradation involved a simple decarboxylation of the acid,
forming methane from the methyl group and carbon dioxide from the carboxyl
froup.   Opposing this view, Barker (2) held that methane was always formed
:om reduction of carbon dioxide.
The controversy was partially ended when Buswell and Sollo (3) added
C14 labeled carbon dioxide in the form of sodium bicarbonate to an acetate
utilizing methane culture.    They found very little of the methane produced
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