50    AEROBIC DECOMPOSITION OF VARIOUS CELLULOSIC
SAMPLE TYPES IN LAND DISPOSAL
Susan A. Harris, Staff Engineer
Harding Lawson Associates
Oakbrook Terrace, Illinois 60181
E. E. Cook, Professor and Associate Dean
College of Engineering
Southern Illinois University
Carbondale, Illinois 62901
INTRODUCTION AND PREVIOUS RESEARCH
This study focused upon the aerobic decomposition (by mass) of cellulosic material buried in soil.
The variables considered in this study included cellulosic sample type, sample surface area, moisture
content of the surrounding soil environment, temperature, the effect of additional nutrients, oxygen
requirements, and time.
The majority of research previously conducted in this field refers to gas production in landfills. As
gas production parallels decomposition, the previous data is applicable to decomposition by mass as
well.
General Microbiology and Chemistry
Municipal solid waste stabilization can be divided into two main biological stages: an aerobic
decomposition phase and an anaerobic phase which develops when available oxygen has been
depleted.
In the first step of decomposition, complex organics are altered by both facultative and anaerobic
bacteria, generically called acid formers, as they produce organic fatty acids. Facultative anaerobes
aid in the decomposition of materials and reduce the redox potential so that methanogenic bacteria
can grow. The acid fermentation yields a low pH leachate with high volatile acid concentrations and
considerable concentrations of inorganic ions. The organisms of this stage appear to be far more
tolerant of environmental stresses than those of the methanogenic stage.
In the second stage, organic acids are consumed by a special group of methanogenic bacteria (of the
genus Methanobacterium) and converted to methane and carbon dioxide. These methanogenic bacteria are strictly anaerobic and cannot perform in the presence of even small amounts of oxygen.1
There appears to be a general pattern of gas production in a landfill environment, as shown in
Figure 1. Four distinct phases have been noted: Phase I aerobic; Phase II anaerobic nonmethano-
genic; Phase III anaerobic methanogenic unsteady; and Phase IV anaerobic methanogenic steady.2
If the balance between methaneproducing and acidforming organisms is upset during the start of
the methane fermentation process, an organic acid increase and corresponding drop in pH could
occur, causing a severe setback to the methane production process. The balance could be upset by
various factors including shock loading, temperature fluctuations, and inhibitory materials.
A variety of physical, chemical and biological activities may control the presence or absence of a
constituent in a landfill, and can alter chemical species and influence the physiology of degrading
microbial populations.'. Several variables have been separated for discussion as follows.
Cellulosic Sample Source
In general, any waste which can be treated aerobically can also be treated anaerobically. One of the
few exceptions to this generalization is lignin, the amorphous polymeric substance which binds
cellulose fibers in wood.1,2 Lignin is very resistant to decomposition and is even insoluble in water; it
will not hydrolyze into products which are more easily degraded.3
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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