[USCC] Oxygen In Composting

Sun Mar 22 09:48:55 CDT 2009

John,

You asked about the relationship between oxygen and carbon dioxide. That is what my graph shows. I also pointed out that based on our 30 years of experience when oxygen levesl dropped below 5% we had a significant number of zones with little or no oxygen and were anaerobic. In thise cases we were able to measure small amounts of methane. Hence we recommended that piles (windrows) maintain oxygen levels above 10%. Higher levels were acceptable as long as the piles did not cool off appreciably and were able to maintain temperatures needed for pathogen destruction. As a point of interest my Ph.D thesis was on oxygen and carbon dioxide in soil in relation to the potential for organic matter decomposition. This was in 1955. Since then many excellent papers were written.

There is a large volume of literature on popultion trends during composting. From the 1980s by Strom, finstein and Morris in 1974, Poincelet, 1977,Britton and Droffner in 1994, Palmisano in 1996, Walke, 1975, Epstein 1997 etc. etc., etc. 

Eliot

-----Original Message-----
From: compost-bounces at mailman.cloudnet.com [mailto:compost-bounces at mailman.cloudnet.com] On Behalf Of John A. Crockett
Sent: Thursday, March 19, 2009 11:33 AM
To: U.S. Composting Council listserve
Subject: [USCC] Oxygen In Composting

Regarding oxygen in composting, Eliot Epstein said: "Take a look in my book The Science of Composting pg. 27" which I just did, and to me, that does not answer my question.  It shows two graphs, Y axis oxygen, Y' axis CO2, and the X axis days.   I saw nothing on the rate of air flow. The oxygen could have been held at any level by adjusting the RATE of air flow.  I am well aware that oxygen consumption varies with the population of oxygen consumers, and that there are many management practices that affect the population, and that early in the process, there seems to be the greatest opportunity for the highest populations of active bacteria.  If the oxygen is low, it is easy enough to provide more aeration, a greater rate of air flow, provided the aeration system has been designed to enable varying the RATE of air flow, vary the cubic feet per minute. 

It is very easy to maintain oxygen at any given level by varying the RATE OF AIR FLOW to coordinate the aeration with the microbial oxygen consumption.  

I want, and firmly believe that we need info on population and / or bio-mass of active bacteria and fungi at various concentrations of oxygen and/or CO2.

We're frequently needing to provide over 13X, and 23X is not uncommon, the volume of compost, in fresh air every hour, to hold the CO2 down between 1 - 2%, and at the same time we're sustaining temperature < 155°F.

Since I am naïve enough to believe that improving the composting process is going to require being a lot more aware of what is happening in the composting mass, and how that changes with our changing the oxygen and moisture levels, turning to homogenize, to improve porosity, while also getting the porosity to be more uniform, while also averaging out the microbial distribution throughout the composting mass; I just spent about 15 minutes looking at a tiny sample at 40X (microscope magnification) and found it interesting to see what appears to be a lot of fungal hyphae showing up.

I consider this sample to still be 'early stage', since the heating and oxygen consumption suggests to me that there is a lot of bacterial activity.  Can fungi generate nearly as much heat at bacteria?  I don't know!

So, we're back at the question:  What is the definition of "aerobic" in concentration of oxygen in the composting mass?  Is there any definitive percentage of oxygen that qualifies as aerobic?  And if so, what is the basis for that definition?  I suggest that maybe 15% oxygen be accepted as aerobic and that ≥ 17% is better; and that CO2 should be ≤ 5% with ≤ 2% being a lot better.  I think this is what the microbes 'need' to be able to meet the challenges that homo sapiens have created, that we're depending on them to solve.

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

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