Millistak+HC AppGd_textC.qxd - Millipore

Why Are Millistak+ HC
Filters Better?
Biological solids exhibit poor filter
cake properties—very thin deposits
exhibit very high flow resistance.
The capacity of a clarifying depth
filter is, therefore, highly dependent
on the accessible internal surface
area available for particle deposition.
For a given media type and grade,
capacity increases linearly with
thickness or bed depth. Moreover,
as commonly occurs in biological
suspensions, the particles span a
broad range of sizes—to maximize
capacity, the filter media must be
structured to accommodate these
particle sizes in proportion to their
number. For this reason, a gradient
pore structure or media density
is optimal.
Outperforms the Competition
Based on these design criteria,
Millistak+ HC filters have been
developed to outperform all competitive
depth filters. Each cellulosic
pad within the multilayer composite
possesses a graded pore structure
from front to back. Coupling two
such pads in series expands the
effective pore size range by as
much as several orders of magnitude.
In addition, Millistak+ HC filters
employ two full-thickness cellulosic
pads for an overall bed depth of more
than 0.260 in.—thicker than any
other cellulosic depth filter on the
market today.
Unique Membrane Layer
Improves Performance
A major advance in the design of
stacked-disk prefilters, as offered in
Millistak+ HC filters, is the incorporation
of a microporous membrane layer,
downstream of the cellulosic pads.
The membrane layer delivers two
important advantages. First, it serves
as a final barrier to trap small particles
and colloids that would otherwise
foul a trailing sterile filter. Secondly,
the membrane contributes a modest
hydraulic resistance to the filter,
which significantly improves feed
flow distribution and, consequently,
media utilization. All vertical stackeddisk
designs inherently force a greater
percentage of feed flow to the lower
sections of the filter column, which
are under higher hydrostatic pressure.
The addition of the microporous
membrane to Millistak+ HC filters
helps to minimize this vertical pressure
gradient, to utilize all available filter
area more evenly and efficiently.
Millistak+ HC Filters Application Guide 5