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Biodeterioration of Pulpwood and Paper |
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Biodeterioration
of
Pulpwood
and
Paper -
It
is
conservatively
estimated
that
10
percent
of
all
the
pulpwood
cut
is
lost
through
the
activity
of
decay
organisms,
mainly
fungi.
Temperature
and
moisture,
together
with
an
adequate
supply
of
oxygen,
are
the
chief
environmental
factors
which
influence
the
rate
of
wood
decay.
Adequate
nutrients
are
present
in
the
substrate.
The
fact
that
the
wood
decay
fungi
are
aerobic
has
prompted
a
number
of
paper
mills
to
store
wood
under
water,
either
totally
submerged
or
sprayed
continually.
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This
greatly
reduces
losses
due
to
microbiological
degradation.
Wood
degradation
by
microorganisms
is
usually
classified
by
the
gross
effect
it
has
on
the
characteristic
of
the
wood.
White
rots
are
characterized
by
the
degradation
of
brownish
lignin,
leaving
a
white
spongy
cellulosic
mass
in
the
wood.
Brown
rots
are
the
result
of
preferential
microbiological
degradation
of
the
cellulose
leaving
behind
a
brown,
pinky
mass
with
a
predominance
of
lignin
Basidomycetes
generally
cause
the
white
and
brown
rots.
A
significant
degradation
occurs
by
the
softening
of
the
surfaces
of
stored
moist
wood.
These
are
the
soft
rots
caused
by
the
Ascomycetes
and
some
Fungi
Imperfecti
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Paper
pulp
is
nothing
more
than
wood
which
has
been
disintegrated
by
chemical
or
mechanical
means.
Chemically
produced
pulp
provides
less
nutrients
for
microbial
growth
than
do
mechanically
produced
pulps.
This
is
because
the
chemicals
used
in
pulping
solubilize
much
of
they
wood
substance,
leaving
cellulose
and
some
lignin.
Biodeterioration
is,
therefore,
greater
during
storage
of
mechanical
pulp
than
it
is
during
storage
of
chemical
pulp.
The
use
of
pulp
infested
with
fungi
or
bacteria
can
result
in
poor
quality
of
sheet.
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The
strength
of
the
sheet
is
impaired
in
some
cases
where
decay
fungi
are
present.
Also,
it
is
difficult
to
completely
redisperse
fiber
contaminated
by
fungi.
If
the
fiber
cannot
be
completely
dispersed,
small
knots
or
masses
of
fiber
and
fungal
hyphae
will
cause
spots,
specks,
and
holes
in
the
sheet.
The
use
of
badly
contaminated
pulp
will
introduce
large
numbers
of
microorganisms
into
the
papermaking
system.
Many
of
these
organisms
can
develop
and
grow
into
slime
deposits
in
the
paper
mill
and
cause
problems
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The
development
of
slime
depends
largely
upon
the
nature
of
the
pulping
operations.
Slimes
appear
in
the
paper
sheet
in
the
form
of,
undesirable
slime
spots.
Slime
is
caused
by
the
deposition
of
microorganisms
and
the
Subsequent
entanglement
of
fiber,
fines,
and
other
debris
from
the
water,
and
components
of
the
papermaking
medium.
Bacteria,
particularly
capsulated
bacilli,
are
the
most
important
single
group
of
slime
formers.
Among
these,
Aerobacter
aerogens
and
Bacillus
spp.
are
quite
common.
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The
filamentous
iron
bacteria
Sphaerotilus
natans
can
be
found
as
part
of
the
slime
mass
on
those
paper
machines
operating
above
pH
5.5.
Alcaligens
viscosus
var.
dissimilis
has
been
identified
in
pink
slime
from
a
number
of
mills.
Desulfovibrio
spp.
are
common
anaerobic
bacteria
found
where
oxygen
is
absent
or
minimal.
Fungi
identified
as
causes
of
slime
deposits
include
species
of
Mucor,
Penicillium,
Fusarium,
and
Trichoderma.
Yeasts
such
as
Torula
and
Rhodotorula
are
fairly
common
Finished
paper
is
also
subject
to
microbiological
attack.
Cellulose,
the
principal
constituent
of
paper
is
susceptible
to
degradation
by
a
great
many
species
of
fungi
and
some
bacteria.
The
paper
industry
uses,
a
large
number
of
chemicals
in
the
process
of
making
paper.
These
chemicals
may
be
added
to
the
fiber
and
water
prior
to
forming
the,
sheet,
i.e.
internal
additives.
Chemicals
may
also
be
added
to
the
surface
of
the
sheet
after
sheet
formation,
such
as
surface
sizes
or
coatings.
Many
of
the
additives
or
coating,
are
subject
to
microbial
degradation.
Under
conditions
permitting
growth
microorganisms,
the
paper
may
be
stained
or
discoloured
by
the
products
of
microbial
metabolism.
Growth
of
cellulolytic
microorganisms
will
produce
perforations,
weaken
fibers,
and
completely
destroy
the
paper
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