51    ANAEROBIC BIODEGRADABILITY OF NEWSPRINT-BASED
MATERIALS
Wei-Min Wu, Research Engineer
De-Ming Li, Research Associate
Mark Ruppel, Associate Scientist
Lakshmi Bhatnagar, Senior Scientist
Robert F. Hickey, Senior Engineer
Michigan Biotechnology Institute,
Lansing, Michigan 48909
INTRODUCTION
Used newsprint and other cellulosic wastes represent a major organic fraction of domestic refuse.
Data indicates that approximately 30% to 60% (average 42% to 45%) of raw refuse is paper products.' Another cellulosic waste is paper mill sludge which is a major waste from the paper and pulp
industries. Both these lignocellulosic materials have little value for reuse and can potentially serve as
an inexpensive source for the recovery of energy via methane production. During the past 20 years,
considerable research has been focused on the biodegradation of mixed organic matter in municipal
solid waste (MSW) to generate methane. These reports, however, do not describe the fate of newsprint
during the anaerobic digestion. Few reports have focused on the anaerobic degradation of newsprint
and other paper products.
Some recent investigation of MSW treatment in landfills has demonstrated that newsprint was not
sufficiently degraded in some cases even after 10 or more years in a landfill. It was also reported that
only 24% of the shredded newspaper's glucose content was degraded to methane.2 The factors
influencing anaerobic biodegradation of newsprint, therefore, appear to require further investigation.
In this study, the anaerobic biodegradability of newsprint in comparison with other cellulosic
products was investigated. The potential of several pretreatment methods to enhance biodegradation,
including shredding and hydropulping of newsprint, removal of ink and oil used for printing by
extraction with methanol, steam explosion and aerobic pretreatment by fungi, were examined. Results
indicate that newsprint was more difficult to anaerobically degrade than other cellulosic and lignocellulosic materials. The biodegradation of newsprint could be enhanced by mechanical (shredding) and
thermal (steam explosion) pretreatment.
BACKGROUND
The major organic components in the newsprint and other lignocellulosic materials are cellulose,
hemicellulose and lignin. Small amounts (generally < 0.3%, w/w) of nitrogen and sulfur are also
present in these materials. Cellulose and hemicellulose can be anaerobically biodegraded. Cellulose is
a linear homopolymer of anhydroglucose units linked by /3-D-l ,4 glucosidic bonds. The stoichiometry
of methane production from cellulose is:
C6H,0O5 + H20 - 3 CH4 + 3 C02 (1)
Assuming complete conversion to methane, the theoretical methane yield is 415 mL CH4 (STP) per
gram cellulose when cell synthesis is ignored. Hexoses including glucose and galactose, pentoses
including xylose and arabinose, and uronic acids are the common monomeric components of hemicellulose. The methane yield from hemicellulose is not defined since hemicellulose is a family of heterpo-
lymers with frequent side chains. Lignin is essentially not degraded since the hydrolysis of lignin is
extremely slow under anaerobic conditions compared with cellulose and hemicellulose.3,4 The lignin
content is low (< 8%) in paper mill sludge from recycled office paper and relatively high (24% to
27%) in less well refined materials such as newsprint.
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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