Re: [compost_tea] Thermophilic stage of composting

From: <soilfoodweb_at_aol.com>
Date: Thu, 29 Jul 2004 03:38:02 -0400
Hi David and Frank -

There are different temperature optima for different species of bio-remediation bacteria and fungi. 

Given that we have some 650 different active ingredients in the pesticide formulations used today, and that the combinations of chemicals results in a nearly infinite number of toxic mixes that have to be dealt with by the biology in soil, or compost, we cannot state that there is single best temperature, a single best set of starting materials, a single best moisture, etc that will always result in decomposition of ALL the toxics in the organic matter.

The best approach is to make sure the compost process goes through a full range of conditions, so that decomposition is optimized, no matter what the combination of pesticides might be present. 

If you know the specific toxin in your compost, then you could search for the SET of bacterial or fungal species that are known to decompose that ingredient, and make sure it is in the compost pile, and make sure the conditions in the pile at which that set of species functions most rapidly.

There are thermophilic fungi, and bacteria, that decompose a number of pesticides.  Because microbial decomposition processes are faster (Q10 effects) at higher temperatures, IF you have thermophilic species present in your compost that can attack the toxics, given the food resources and moisture in the pile, higher temperatures mean faster loss of the pesticide.

But, do you always get the heat-loving species in your pile? 

People have shown good rates of pesticide decomposition at "intermediate" temperatures, and at ambient temperatures, as well as at high temperatures.  Sometimes it has been shown that the fastest rates of decomposition occur at temperatures that are not considered even in the warm temperature ranges.  Why play the game of saying that all compounds will be optimally decomposed at some temperature?  It just isn't that simple. 

The "take-home message" is that you have to know the species of bacteria and fungi in your compost pile in order to know what temperature, moisture, oxygen, food resources and chemical composition are best to maximize decomposition of any particular material. 

We do not have the methods to allow us to assess the bacterial or fungal community on a routine basis.  Even if we were lucky enough to know what species of bacteria and fungi are best for decomposing any pesticide. 

Therefore, it is best to add the widest diversity of kinds of high N, green, and woody materials, in ratios designed to select for a temperature regime that will not result in extremely high temperatures that will kill the organisms, but will allow microbial growth to be rapid, in many different temperatures, moistures, etc.   

Temperature in a compost is strictly the result of BACTERIAL and FUNGAL growth. 

That means, the proper foods must be present to get the bacteria and fungi to grow. 

You have to have enough high N FOODS to get growth rates rapid enough to generate the growth that will result in elevated temperature.  But not too much food, so you kill organisms because the pile bursts into flame.   

Inadequate food?  Inadequate growth to decompose anything.

No organisms?  I don't care how much food you have, without the right biology, there won't be enough heat generated to kill weed seed, human pathogen, plant pathogens or pests.   

As the organisms grow very fast, they use up oxygen.  That means, when temperatures reach high levels, the organisms are using up oxygen faster than oxygen can diffuse into the pile BASED ON THE AIR PASSAGEWAYS INTO THE PILE. 

Chunky materials will allow air to diffuse into the pile, fine-ground materials will result in lack of oxygen diffusing into the pile. 

Therefore, temperature gives you a good idea about oxygen in the pile, as long as you control particle size carefully, and don't let the pile becomse anaerobic.  Once the pile has crossed that threshold into anaerobic conditions, and the metabolic products produced in anaerobic conditions, all bets are off about the relationship between oxygen and temperature. 

Decomposition of complex ring-structures in pesticides is an AEROBIC process.  The catecholases, or the enzymes made by microbes to break down the most toxic portions of many pesticides, are only produced in aerobic conditions.  

So, is it really important to categorize whether decomposition processes are occurring in cool, warm, or hot conditions? 

Only if you know what organisms are present, and whether the pile will remain aerobic.  And, whether the organisms have adequate energy sources (food) to grow, and adequate moisture, and.... 

I've made my point, right?  Generalizations are just plain not-useful, given what we don't know about the organisms in compost, and what makes them grow, or not. 

--
Elaine Ingham
President, Soil Foodweb Inc.
SFI Corvallis, OR
SFI Port Jefferson, NY
SFI Lismore, NSW, Australia
SFI Hilversum, The Netherlands
SFI Cambridge, New Zealand
SFI Culiacan, Mexico
SFI Jerome, Idaho
http://www.soilfoodweb.com


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Received on Thu Jul 29 2004 - 05:54:33 EDT

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