[Digestion] Analytical Data on Feedstocks

[Steve Verhey]

This is something I happen to know a little about, having left academia to 
start a biodiesel company (cwbiodiesel.com). I can't help much regarding 
biodiesel, and I can't help at all with the ethanol part of the question, 
though.

First, if I could bore you with some background on the glycerin-as-waste 
issue, which is becoming something of a myth. I get calls every week from 
businesses all over the country looking to buy our glycerin. Primarily the 
calls are from animal feed companies, who are looking to replace 
increasingly expensive corn with a cheaper source of calories. So glycerin 
is already being used in anaerobic digestion, only inside cattle. There are 
other uses as well, as industrial chemists learn to use glycerin as an 
alternative to petroleum as a source of carbon for synthesis and 
fermentation.

Biodiesel synthesis uses an approximate 2x molar ratio of methanol to 
triglyceride fatty acids, and most of the residual methanol winds up in the 
glycerin phase. Large biodiesel producers recover the methanol, smaller 
producers generally don't, yet. (Of course, methanol must be removed before 
any use in feed.) In addition, catalyst cations (generally Na or K), water, 
partially-reacted mono- di-glycerides, and other unreacted material (for 
example, phosphatidylglycerides) end up in the glycerin. Virtually 
everything in the glycerin would turn into CO2 or methane, leaving only P 
and K or Na. K, of course, has fertilizer value, so it would be worth 
choosing it where possible. Unfortunately, Na is more widely used in the 
industry.

My personal favorite possible use for glycerin is exactly the one proposed 
by Mr. Gould, and I'm sorry MDEQ is being so, well, regulatory. I've done a 
quick search online and looked in my files, and I don't see the information 
MDEQ is asking for. Would they accept a description of what goes in and what 
comes out of the biodiesel reaction? There are fairly strict standards for 
metals in biodiesel, and any metal content in the glycerin should be 
negligible. I'd be very surprised if there were data in the literature 
regarding solids from AD using biodiesel glycerin.

I'm sorry I'm so little help here, and the information may still be out 
there. Come to think of it, presumably feed companies had done analyses on 
the glycerin they use -- maybe they would share it.  I do think MDEQ is 
barking up the wrong tree: I'd be much more worried about flammability 
issues from residual methanol than any of these other things.

Steve Verhey, Ph.D
Biologist at Large
CEO, Central Washington Biodiesel

>From: "M. Charles Gould" <gouldm at msu.edu>
>To: digestion at listserv.repp.org
>CC: Michelle Crook <CrookMi at michigan.gov>
>Subject: [Digestion] Analytical Data on Feedstocks
>Date: Fri, 25 May 2007 09:49:21 -0400
>
>I work with farmers in West Michigan on manure management issues, and
>for the past several years have focused a lot of my time on anaerobic
>digestion as a component of a sustainable manure management plan. The
>increased numbers of biodiesel and ethanol plants in Michigan have
>presented the opportunity for dairy and swine farmers with digesters
>to use glycerin (a biodesiel by-product) and syrup stillage (an
>ethanol by-product) with manure to increase gas production. The
>mixing of these feedstocks has caught the eye of the Michigan
>Department of Environmental Quality (MDEQ). Because there are no
>regulations per se that deal with anaerobic digesters and products
>coming from anaerobic digesters, the MDEQ is feeling threatened and
>has given us a huge list of VOCs, SVOCs and metals to test for in
>order to get a solid waste exemption. The agriculture community has
>been down this road before in terms of exorbitant analytical testing
>required by the MDEQ, most recently with composting manure and animal
>mortalities. We want to avoid as much hassle as possible. Both myself
>and a colleague from the Michigan Department of Agriculture have
>mined the web for information and have talked with people we thought
>may have analytical data to show what is in the feedstocks and what
>is in the solid and liquid digestate after digestion. We are coming
>up empty for the most part, so I am asking you, an international
>audience, for some help. Can you direct me to published analytical
>data that shows the VOC, SVOC and metals content of feedstocks (such
>as glycerin, syrup stillage, food processing residuals, etc.) prior
>to going in a digester and the VOC, SVOC and metals content of both
>the liquid and solid digestate after digestion where various
>feedstock were added to manure?
>
>Thank you for considering my request, and I look forward to your response!
>
>Charles Gould
>Grand Haven, MI
>USA
>
>
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