[Digestion] Giant reed (arundo donax) digestion

[David]

Les, all,

On 9/23/2011 11:19 AM, Les Gornall wrote:
> Good question!  The [arundo donax (giant reed)] is unique in it's ability to lock silicon into its stem tissues.  That's why it is used for making oboe reeds.

A more ubiquitous high silica plant, at least around here (Oregon) 
where I live is equisteum, variously known as scouring rush and horsetail.

> When digested the silicone would most likely be expresses as siloxanes in the Biogas.  But I have not seen any data.

I tend to doubt that any resulting biogas would have siloxanes in it. 
It's not my area of expertise, but my understanding is that the 
siloxanes found in landfill gas are not "built up" from any natural 
silica compounds, as would have to be the case if they were to be 
produced simply because one is digesting natural organic matter that 
has a lot of silica, but rather they result from the decomposition of 
artificial silicates:

    Volatile Methyl Siloxanes (VMS) are the result of hydrolysis of
    Polydimethylsiloxane (PDMS), an organosilicon compound which is
    used in a wide range of consumer applications. Due to its
    widespread use, PDMS is deposited in landfill where it degrades in
    lower molecular weight compounds (VMS). PDMS can also enter the
    wastewater treatment plants were, because of its insolubility in
    water, partitions to the sludge. Consequently, when this is fed to
    anaerobic digester, PDMS can hydrolyse to VMS.

    The species detected by now in biogas are
    hexamethylcyclotrisiloxane (D3), decamethyl-cyclopentasiloxane
    (D5), octamethylcyclotetrasiloxane (D4), hexamethyldisiloxane
    (L2), octamethyltrisiloxane (L3). The concentration values depend
    on the origin of the biogases. [found here
    <http://www.tf.uniag.sk/Biohydrogen/state.htm>]



I am not familiar with giant reed grass, but I have seen reeds of the 
sort used in instruments, and clearly one of the main characteristics 
of those reeds is their stiffness; they have to vibrate to fulfill 
their function. If that is characteristic of the plant generally-- 
stiff, woody-- then I think it would make a very poor biogas substrate 
unless it was harvested while still at a tender stage, or perhaps 
exposed to fungi post-harvest. I would in general assume that one 
could learn more about pretreatment options by researching what is 
done with more widely used crops of the same general sort-- 
miscanthus, switchgrass, et al.


d.
-- 
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

|
"Make no search for water.       But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)

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