Capturing the Heat from Aerobic Compost

by John Crockett

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Organic Matter is going to decompose with time, and, we can capture the Surplus Microbial Metabolic Heat from the early stage of the composting process.

Our process for capturing the heat from composting seems to be best suited to large scale greenhouse growers, particularly if they are part of a nursery operation or commercial growing of organic produce.   Heating 20 acres of greenhouses in lower New York State and like climates, is estimated to save about 1 million gallons of heating oil a year.  AND, it can be done, economically, but not with the commonly used methods of composting.

Oxygen_Depletion.gif (9223 bytes)Assisted or 'forced' aeration is essential to provide the bacteria in active compost with the oxygen that they need, to work effectively.  I like the term "assisted", simply because the pressure or vacuum is so very little, generally significantly less than 1"wc (water column), as measured on a manometer, and often in the range of 0.10", sometimes as little as 0.020"wc.... far less pressure or vacuum than most people are equipped to measure.  The volume of air required is significant, often over 10cfm of fresh air, per cubic yard of compost, to hold the CO2 at 2% or less, which means that the oxygen level is > 18%.

While we have been able to easily get compost temperatures in the 150 - 160F range, we are currently doing research to see what temperatures yield the highest numbers of active bacteria.  At the present time, we are seeing preliminary data that is suggesting that those high temperatures are not the best temperature range, from the point of view of active bacteria populations.  We are doing more research, which is part of our quest to constantly improve our knowledge and systems.

Best Management Practices dictate that composting should be done on a concrete pad with the aeration veins built into the concrete pad.  Trapezoid shaped piles mean about 3 times more compost per acre, than with traditional windrow format.  The idea that windrows aerate passively by convection seems to be a sacred myth.  Our research, doing extensive cross section profile oxygen and CO2 testing convinced us that it doesn't work well in the real world.  That wipes out any benefit to windrow format, because assisted aeration can work just as well with trapezoid format, with about 3 times more compost per acre, better utilization of the investment in the concrete pad.

Best Management Practices also dictate that the off-gas from early stage compost should be sent through a bio-filter.   Our experience is that our off-gas has > 18% oxygen.  Why not send that air through the older compost, that still needs the assisted aeration to provide the microbes with enough oxygen...  One blower, pulling the air through the early stage compost, then the output air from the blower sends the air to the older compost, which very nicely doubles as a bio-filter.  A key is that there needs to be at least twice as much compost volume serving the bio-filter function, compared to the newer compost, which frequently has some rather unfriendly odors, even with oxygen maintained > 18%.


Setting up a system to capture the heat takes time, and now is none too early to contact us, to start to plan, so you have a fully functional system for next winter.  Much of the work of installing a system is in building the composting pad, with the aeration veins and aeration manifold system, all of which is best located close to where the heat is going to be used.     In idea situations, the composting becomes a profit center of its own, completely covering the cost of installing the concrete pad and aeration system, so that the heat becomes a giant bonus. 

We've been designing and building composting aeration systems for ten years, and, we've learned a lot from experience.   Early on we had some interesting learning experiences, we encountered problems, and learned how to overcome them, so that now, our systems are very efficient.

While in 2005-2006 we had one compost research silo adapted for heat capturing, by 2006-2007 we have three. We've got enough hands on experience to know that we can capture a great deal of the Surplus Microbial Metabolic Heat from the composting process.  We've got a patent pending on the process for capturing the heat.  Going beyond that, our technology for managing the compost, so there is enough Surplus Microbial Metabolic Heat to be worth capturing is equally important..

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Contact us today,
John Crockett
e-mail, jac@magicsoil.com
1 (845) 225-7763


This page was last updated: 03/15/2011 10:00 PM