[USCC] What is "Aerobic" as far as % oxygen content

[John A. Crockett]

I agree with Rufus Chaney when he says there is a lot of "Art" to
composting.  I'll add, that I think a good composting process manager has a
lot of intuition, usually (L)Earned through years of hands on experience,
and continually asking how we can improve the process.

We adjust the rate of air flow, trying to hold the CO2 level between 1 - 2%,
and often that requires, with the feedstocks and the way we pre-process and
manage our compost, to require over 20 times the volume of compost, in fresh
air, every hour.  And even with that rate of air flow, we often see
temperatures > 160°.  We adjust the flow rate, and believe that on/off
aeration is no better than it would be for us.  I think I would have a real
hard time functioning if some of the time the air I breath had less than 15%
oxygen in it, so we use continuous aeration, 24/7.  While we call it
"forced" aeration, often the "force" is < 0.300"wc; and often a change of
0.030"wc will massively change the rate of flow.  Of course we need to use a
fine digital manometer to monitor pressure / vacuum in those ranges.  

And, certainly we often get significant foul odors in the off-gas from early
stage food composting, even with the oxygen level ? 17%.  Since we use
negative pressure on the early stage compost, we have custody of that
off-gas, and turn around and send it through older compost, which still
needs aeration, and very conveniently also doubles as a dynamic bio-filter.
At least, I've read that all fungi are strict aerobes, meaning that they
need oxygen.  I still don't know what the tolerance range is for oxygen for
optimal fungal activity, and if anyone knows that, I would appreciate that
information.

Our first oxygen depletion research was over 13 years ago, and we found that
the microbes could crash the oxygen level from 19% down to 2% in 15 minutes.
Much of that information has been available to everyone with internet
access, since we opened www.magicsoil.com in May of 1998.  Of course, how
fast the microbes crash the oxygen level in the absence of full time forced
aeration probably depends on how many active microbes are consuming oxygen,
are working at getting the composting job done.

If composting is a "profession", it seems to me that there ought to be a
definition for "aerobic" defined as a % oxygen content, and that definition
ought to be based on what level will support a specific population of
bacteria and / or fungi, whether that level of active bacteria be 5E+6, or
3.0E+9, per gram, dry weight.  Then, complicating that is particle size.  We
shred to < 1/8" because turn around time translates to how quickly we can
use that space for more incoming material.

Working Together to Create a Sustainable Environment,
John A. Crockett, a.k.a. Dr. Mike Robe
Mother Nature's Farms
(845) 225-7763
http://www.magicsoil.com/
jac at magicsoil.com