Typically the idea is to avoid producing these gasses, so most of what I've read so far is geared towards that. This is
something that I've never tried myself, so I have little idea as to what the yield would be, or what the optimal conditions are.
Just on a whim, I added 0.9g of pulverized grass and root bits to a 3mL syringe; added 0.1g Mg(NO3)2 to 0.56g of DI
H2O,
and suctioned it into the syringe; and then carefully removed as much air from the syringe as possible and capped it.
I got quite busy this morning and forgot the syringe at home. When things slow down today I'll bring it into work and incubate
it over the weekend. In years past when I put green grass clippings into a sealed syringe (without added water), within
several hours I start seeing gas fill up the syringe. I think this was mostly CO2, and it was produced mostly in the
beginning when there was still some oxygen left in the syringe.
When I'd add water to the grass, over the next several days the pH would drop. Adding Mg(OH)2 in small amounts
after a week or so would help raise the pH, since I was trying to make methane (I succeeded at the time).
After sitting overnight at room temperature, my syringe is still sitting there quietly, without producing any obvious amount of
gas. I probably shouldn't have added water to it.
My understanding is that nitrates eventually get reduced to nitrogen, with nitrite as an intermediate step. If the nitrite
levels are high enough, and other volatile fatty acids are being produced, some of the resulting nitrous acid decomposes, with
some NO escaping from the fermentation. If the environment remains sealed, then eventually nitrogen is the end product.
Buffering the pH lengthens the time that the fermentation continues, and produces more VFAs.
I think the problem with silo gas is more likely to happen naturally in drought-prone areas. Here in Texas it's a bigger problem, I
think. It sounds like you're used to being on and around farm operations, but I'll mention it for other's benefit, that
fermentations can produce some interesting and sometimes unexpected gasses. Methane, carbon dioxide, sulfides, nitrogen oxides,
and possibly even cyanides. So, be careful. Some cattle down here got turned loose in a field that had just recovered from a
drought, and most of them died from cyanide poisoning. It turns out the grass had developed high cyanide levels.
http://www.wired.com/2012/06/cyanide-and-poisoned-cows/
I don't claim to know much about the grass fermentation process, I just play around in the lab from time to time. |