Re: [DIYbio] Wood filter

here's the original article link:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0089934

TL;DR:

Xylem Structure and Rationale for ue of Conifer Xylem:
Angiosperms (flowering plants) have xylem conduits called vessels that
are derived from several cells arranged in a single file, having
diameters up to 0.5 mm and lengths ranging from a few millimeters to
several meters [7]. These parallel conduits have closed ends and are
connected to adjacent conduits via "pits" [8] (Figure 1d,e). The pits
have membranes with nanoscale pores that perform the critical function
of preventing bubbles from crossing over from one conduit to another.
The porosity of the pit membranes ranges in size from a few nanometers
to a few hundred nanometers, with pore sizes in the case of
angiosperms tending to be smaller than those in gymnosperms.

Construction of the Xylem Filter:
1 inch-long sections were cut from a branch with approximately 1 cm
diameter. The bark and cambium were peeled off, and the piece was
mounted at the end of a tube and sealed with epoxy. The filters were
flushed with 10 mL of deionized water before experiments. Care was
taken to avoid drying of the filter.
The xylem filter device was constructed by simply peeling off the bark
and cambium from a section of the pine branch and inserting it into a
tube (Figure 2a). Although a simple tube fastener could provide a
leak-tight seal between the tube and the xylem, we used epoxy to
ensure that there was no inadvertent leakage. When deionized water was
loaded into the tube above the xylem and subjected to pressure in the
0.5-5 psi (3.45 to 34.5 kPa) range, we found that water readily flowed
through the xylem. The flow rate was proportional to applied pressure

Conclusions:
Pigment filtration experiments revealed a size cutoff of about 100 nm,
with most of the filtration occurring within the first 2-3 mm of the
xylem filter. The xylem filter could effectively filter out bacteria
from water with rejection exceeding 99.9%.
Pit membranes were identified as the functional unit where actual
filtration of the bacteria occurred.
Flow rates of about 4 L/d were obtained through ~1 cm2 filter areas
at applied pressures of about 5 psi, which is sufficient to meet the
drinking water needs of one person.

The simple construction of xylem filters, combined with their
fabrication from an inexpensive, biodegradable, and disposable
material suggests that further research and development of xylem
filters could potentially lead to their widespread use and greatly
reduce the incidence of waterborne infectious disease in the world.


On Fri, Feb 28, 2014 at 9:54 AM, leaking pen <itsatrap@gmail.com> wrote:
> http://www.upi.com/Science_News/2014/02/27/MIT-scientists-show-tree-branch-to-be-effective-water-purifier/7811393531999/?spt=mps&or=1
>
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--
-Nathan

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