<br><font size=2 face="sans-serif">For what its worth one thing we are
seeing in certain areas is some level of siloxanes in biogas applications
where industrial grade detergents are used for washing down of areas and
flow into the biogas feedstock. </font><br><br><font size=2 face="sans-serif"><br></font><img src=cid:_1_09FBC3B809FBC270005A5F458525791B><br><br><br><table width=100%><tr valign=top><td width=40%><font size=1 face="sans-serif"><b>Duncan Martin <duncanjmartin@gmail.com></b></font><br><font size=1 face="sans-serif">Sent by: digestion-bounces@lists.bioenergylists.org</font><p><font size=1 face="sans-serif">09/30/2011 12:23 PM</font><table border><tr valign=top><td bgcolor=white><div align=center><font size=1 face="sans-serif">Please respond to<br>For Discussion of Anaerobic Digestion <digestion@lists.bioenergylists.org></font></div></table><br><td width=59%><table width=100%><tr valign=top><td><div align=right><font size=1 face="sans-serif">To</font></div><td><font size=1 face="sans-serif">david@h4c.org, For Discussion of Anaerobic
Digestion <digestion@lists.bioenergylists.org></font><tr valign=top><td><div align=right><font size=1 face="sans-serif">cc</font></div><td><tr valign=top><td><div align=right><font size=1 face="sans-serif">Subject</font></div><td><font size=1 face="sans-serif">[Digestion] Silicones, siloxanes and
the like</font></table><br><table><tr valign=top><td><td></table><br></table><br><br><tt><font size=3>There's a common confusion here - a familiar one between
chemical substances with similar-sounding names.......</font></tt><br><br><tt><font size=3>Just as <b>alkanes</b> (eg methane, propane, hexane
and all the paraffin family) are not remotely related to<b> alkalis</b>(eg caustic soda and similar metal hydroxides), so <b>silicon</b> (a non-metallic
element) is only distantly related to the <b>silicone, siloxane</b> and
other synthetic compounds that can cause minor problems in landfill gas
and the digestion of municipal wastes. </font></tt><br><br><tt><font size=3>Broadly speaking, <b>silicon</b> is commonly
found in plants (esp grasses) in the form of silica (silicon oxide) and
in many minerals as <b>silica </b>(eg sand) or <b>silicates</b>. These
materials aren't digestible, so they cause no problems in biogas. They
may accumulate in your digester or cause wear of moving parts - but many
other minerals can do the same. Good design should deal with such issues
easily enough.</font></tt><br><br><tt><font size=3><b>Silicones, siloxanes</b> etc are fairly
exotic synthetic compounds used in small quantities (usually) in many modern
products - ranging from cosmetics via sealants to breast implants. They
resemble organic (carbon-based) compounds but with the carbon replaced
by silicon. They commonly include hydrogen and oxygen as well as silicon
- and maybe other elements too.</font></tt><br><br><tt><font size=3>When these compounds get into any kind of
digestion system, traces can end up in the biogas - and when they burn,
they form silica. Sand, in effect. In a heating application, this shouldn't
be a huge problem. However, in any kind of gas engine used for electricity
generation, the effect is similar to regularly slipping a few grains of
sand into the fuel tank of your car. Not good for engine life! </font></tt><br><br><tt><font size=3>It follows that silicon compounds would not be expected
in the biogas produced from the digestion of crops, manures and other natural
substrates, even if the feedstock is high in silica etc. </font></tt><br><br><tt><font size=3>Moral 1: don't worry about silica!</font></tt><br><tt><font size=3>Moral 2: read the names of chemicals with care - and
don't guess about relationships!!</font></tt><br><tt><font size=3>Moral 3: remember that tabloid reporters who write
about aspiring starlets getting "silicon" implants probably ended
up in that job because they failed Science 1.01!!!</font></tt><br><br><tt><font size=3>Duncan Martin</font></tt><br><tt><font size=3>Cloughjordan Ecovillage</font></tt><br><tt><font size=3>Ireland</font></tt><br><br><br><br><br><tt><font size=3>On 27 September 2011 23:26, David <</font></tt><a href=mailto:david@h4c.org><tt><font size=3 color=blue><u>david@h4c.org</u></font></tt></a><tt><font size=3>>
wrote:</font></tt><br><br><font size=3 face="Georgia">Les, all,</font><br><br><tt><font size=3>On 9/23/2011 11:19 AM, Les Gornall wrote: </font></tt><br><br><tt><font size=3>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. </font></tt><br><br><br><tt><font size=3>A more ubiquitous high silica plant, at least around
here (Oregon) where I live is equisteum, variously known as scouring rush
and horsetail.</font></tt><br><br><tt><font size=3>When digested the silicone would most likely be expresses
as siloxanes in the Biogas. But I have not seen any data. </font></tt><br><br><br><tt><font size=3>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:</font></tt><br><br><tt><font size=3>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.</font></tt><br><br><tt><font size=3>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 </font></tt><a href=http://www.tf.uniag.sk/Biohydrogen/state.htm><tt><font size=3 color=blue><u>here</u></font></tt></a><tt><font size=3>]</font></tt><br><br><br><tt><font size=3>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.</font></tt><br><br><br><tt><font size=3>d.</font></tt><br><br><tt><font size=3 color=#8f8f8f>-- </font></tt><br><tt><font size=3 color=#8f8f8f>David William House</font></tt><br><tt><font size=3 color=#8f8f8f> </font></tt><br><tt><font size=3 color=#8f8f8f>"The Complete Biogas Handbook"
</font></tt><a href=http://www.completebiogas.com><tt><font size=3 color=blue><u>www.completebiogas.com</u></font></tt></a><br><tt><font size=3 color=#8f8f8f>Vahid Biogas, an alternative energy
consultancy </font></tt><a href=http://www.vahidbiogas.com><tt><font size=3 color=blue><u>www.vahidbiogas.com</u></font></tt></a><br><br><tt><font size=3 color=#8f8f8f>"Make no search for water.
But find thirst,</font></tt><br><tt><font size=3 color=#8f8f8f>And water from the very ground will
burst." </font></tt><br><tt><font size=3 color=#8f8f8f>(Rumi, a Persian mystic poet, quoted
in Delight of Hearts, p. 77) </font></tt><br><br><a href=http://bahai.us/><tt><font size=3 color=blue><u>http://bahai.us/</u></font></tt></a><br><br><tt><font size=3>_______________________________________________</font></tt><br><tt><font size=3>Digestion mailing list</font></tt><br><br><tt><font size=3>to Send a Message to the list, use the email address</font></tt><br><a href=mailto:Digestion@bioenergylists.org><tt><font size=3 color=blue><u>Digestion@bioenergylists.org</u></font></tt></a><br><br><tt><font size=3>to UNSUBSCRIBE or Change your List Settings use the
web page</font></tt><br><a href=http://lists.bioenergylists.org/mailman/listinfo/digestion_lists.bioenergylists.org><tt><font size=3 color=blue><u>http://lists.bioenergylists.org/mailman/listinfo/digestion_lists.bioenergylists.org</u></font></tt></a><br><br><tt><font size=3>for more information about digestion, see</font></tt><br><tt><font size=3>Beginner's Guide to Biogas</font></tt><br><a href=http://www.adelaide.edu.au/biogas/><tt><font size=3 color=blue><u>http://www.adelaide.edu.au/biogas/</u></font></tt></a><br><tt><font size=3>and the Biogas Wiki </font></tt><a href=http://biogas.wikispaces.com/><tt><font size=3 color=blue><u>http://biogas.wikispaces.com/</u></font></tt></a><br><br><br><br><br><tt><font size=3>_______________________________________________<br>Digestion mailing list<br></font></tt><br><tt><font size=3>to Send a Message to the list, use the email address<br>Digestion@bioenergylists.org<br></font></tt><br><tt><font size=3>to UNSUBSCRIBE or Change your List Settings use the
web page<br>http://lists.bioenergylists.org/mailman/listinfo/digestion_lists.bioenergylists.org<br></font></tt><br><tt><font size=3>for more information about digestion, see<br>Beginner's Guide to Biogas<br>http://www.adelaide.edu.au/biogas/<br>and the Biogas Wiki http://biogas.wikispaces.com/<br></font></tt><br><br><BR>
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