There
are
organic
filters
also.
The
organic
molecules
of
the
filter
attract
the
organic
components
of
the
microorganisms.
An
example,
the
Berkefeld
filter,
utilises
the
substance
diatomaceous
earth,
composed
of
the
skeletal
remains
of
marine
alga
called
diatoms.
Third
type
of
filter
is
membrane
filter
which
received
general
acceptance.
It
consists
of
a
pad
of
organic
compound
such
as
cellulose
acetate
or
polycarbonate
mounted
in
a
holding
device.
Membrane
filters
are
available
in
various
pore
sizes
according
to
the
microorganisms
to
be
trapped.
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