The Biological Degradation of
Lignin from Pulp Mill Black Liquor
F. E. WOODARD, Graduate Research Assistant
O. J. SPROUL, Associate Professor
P. F. ATKINS, JR., Assistant Professor
Department of Civil Engineering
University of Maine
Orono, Maine
INTRODUCTION
The treatment of waste waters from the pulp and paper industry has been a
perplexing problem. The activated sludge method has been able to remove
sugars, and thus, a large portion of BOD. Lignin, however, has not been removed
by this process, leaving a large portion of the COD and nearly all of the color to
be discharged to water courses unchanged.
Schinzel and Benger (1) demonstrated that ligno-sulfonates had moved in a
ground water for a considerable distance and had rendered the water unfit to drink.
Brauns (2) has suggested that it may be possible to find a microorganism capable
of splitting the lignin molecule. He further states that this could lead to a degradation so that the presence of the by-products in streams would not be objectionable. A great need exists for the development of an effective, economically feasible method for the removal of lignin.
It is the purpose of this paper to present the results of research toward the development of an acclimated activated sludge specific for the removal of lignin
found in pulp mill wastes. It will be shown that such a system can remove up to
90 per cent of the lignin and 98 per cent of the color from a solution containing
1,000 mg/l of lignin.
MATERIALS AND METHODS
A prerequisite to the development of an activated sludge was the sampling of
organisms from sources thought to contain lignin degrading organisms. The
sources chosen were a river into which black liquor had been discharged for many
years and an old sawdust pile displaying white-rot. Domestic sewage activated
sludge was also used since it was thought that acclimation might produce a system
capable of removing lignin.
Water from the river was placed in a two-liter cylinder and aerated continuously.
The contents of the cylinder were allowed to settle aaily tor one hr. The top half
of the volume was tnen siphoned off. The cylinder was next filled with an inorganic feed solution as proposed by Gaudy (3). A lignin solution was then fed as
the sole carbon source. Two hundred mg of lignin were placed in the cylinder
each day. The process of siphoning off the top half of the liquid after settling was
intended to encourage the survival of settleable forms of microorganisms while
wasting the nonsettleable forms. The pH of the contents was kept between 5.8
and 7.0. This slightly acid environment was maintained to encourage the growth
of lignin degrading molds. Growth of mixed liquor suspended solids was monitored
by measuring the increase in weight of the sludge mass. Periodic microscopic examination indicated the nature of the suspended solids present.
The domestic sewage activated sludge was, in like manner, placed in a two-
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