Mastodons as models

The American Mastodon (Mammut Americanum) was an inhabitant of the Eastern forest region and the area South of the great lakes until about 13 000 years ago when humans showed up in the area and ate them all. Mastodons were very large herbivores and something of a keystone-species for their ecosystem. They ingested large amounts of rough vegetative matter and partially digested it, leaving it chipped and inoculated, ready to serve as a substrate for tree growth.

It being the end of an ice age, temperatures where still quite low. So Mastodons were well-insulated with a thick layer of fat. They also had a built-in heating system, like all animals: their metabolic activity. As the rough vegetative matter (tree branches, leaves, shrubby growth, etc. but also in more southern areas grasses and less woody foods) passed through their bodies, it provided energy to heat the Mastodon's large body and also for its daily activities. Methane, water gas and carbon dioxide were the main waste products (I'm not counting dung or heat as waste).

I think you can tell what I'm getting at. Do you think it would be possible to recreate conditions similar to those of a mastodon's gut to produce heat, methane and digested woody products?

These conditions would be:
-a large chamber.
-kept relatively warm until it produces its own heat.
-filled with a mixture of water, chipped woody products and bacteria.

What I imagine is a tank integrated into a house instead of a woodstove... Ambitious, maybe too much so.

Note in particular, that this is anaerobic decomposition (fermentation) taking place. This differs from most composting methods.

This is just something that's been on my mind for a while after reading Tim Flannery's book, The Eternal Frontier, where he advocates the re-introduction of megafauna into the North American biome. Worth reading...

Reminds me of the systems built by Jean Pain, which took in green slash from forest undergrowth, and produced compost, building heat, and methane enough to power the trucks and chippers that fed the system, as well as the house's cookstove.

There's a thread on his work here. As with mastodons, soaking the woody material in liquid seems to be important, as this blog points out.

Intersting idea. I think the biggest issue may be the efficiency of using something like this for household heat. Unless the digester was located in the house as you suggested, efficiently capturing, transporting and distributing the heat generated becomes problematic. If the digester was located in the house it would be much more efficient but depending on climate the biomass for "digestion" might be far more than you're willing to carry through the house.
I know this isn't quite the same as what you're envisioning but here is a link to some interesting and detailed examples of heating with compost:
http://www.builditsolar.com/Projects/BioFuel/biofuels.htm#CompostHeat

Yes, this is very similar to Jean Pain's work. As far as I can tell from the few videos available, his pile was huge and he didn't turn it or lead air into it. He also kept it very moist. Both of these factors make me think that what he was doing was actually anaerobically digesting the wood as opposed to composting it. That was the difference and that may be why people have trouble replicating his results or even imagining that they are possible.

Since the processes involved seem to be anaerobic, there is no real reason to have it happen outside and waste all the heat it's generating. The only thing is that you have to think of it before you build the house.

It would make real sense to integrate a concrete (or other thermal mass material) tank into the North wall of a house, inside the house's insulation. You would load it from outside through an insulated door eliminating the problem of carrying woodchips through the house.

The question is how efficient the process of wood digestion is both in practice and in theory (to know what we can strive for). How much heat is generated from how much wood?

I'm trying to get those answers (in theory) now to get an idea of the size of tank that would be necessary.

it would seem the process itself cannot be faulted - whether it would be practical enough to be a viable space heat source might be a different matter - the process could not be conveniently turned on/off so it would then need to be a continuous thing with some method of storing heat that could be turned on/off -

another negative is that, if it should prove too impractical to depend on, it is not possible to then eat the digester - as in the case of the mastadon -

perhaps the old concept once common in eastern europe might fit the bill here - and that was to construct a structure with living space on a second floor for peeeples and room on the first floor for livestock - the livestock generated heat warmed the second floor mainly by convection - this works, of course, only when the peeeples are not overly affected by aroma -

not much aroma to a barn in the wintertime if you keep putting fresh straw down, and you get wonderfull composting action in the bottom layers that makes yet more heat that way

whether it would be practical enough to be a viable space heat source might be a different matter - the process could not be conveniently turned on/off so it would then need to be a continuous thing with some method of storing heat that could be turned on/off -

Good point. Practical seasonal heat storage systems (that have a net benefit) don't exist. At least, I don't think any system has truly been proven to have a net benefit.

Methane digesters have been around for decades.  At best they produce enough heat to keep themselves at the temperture that the bacteria like.  If you tried to take enough heat out of the system to heat a house, digestation would stop--unless it was very, very large.

Mastodons produced more heat in there muscles than in their guts, you don't seem to have a way to do that.

You could just put a couple elephants in the basement. . ..

Just out of curiosity, how would you chew the food for the digester?

homesteadpaul wrote:

You could just put a couple elephants in the basement. . ..

No, no, no!  Elephants are supposed to go on the table where they can be properly ignored!  Didn't your 12-step program teach you anything?

Ok let's forget the mastodon analogy...  It is good to keep in the back of one's mind but not as a blueprint.

After looking around on the internet, I've found that capturing the biogas produced and then purifying it to get methane is all quite complicated.

What I am basically arguing for is to include a compost pile inside the house's insulation layer in any cold climate (we are in zone 5b, Nova Scotia). Have it vented to the outside (or to a well-ventilated indoor space) and loaded through an insulated door from the outside. We need to heat almost continuously for a solid 3-4 months in winter anyway with our woodstove so having the pile constantly provide heat is a good thing. Not being able to turn it off is not an issue. In spring we would take the compost out anyway to spread where it is needed.

Check some of Paul Wheaton's videos.  He's got one where he shows how his compost pile heats the water for his outdoor shower.

joshthewhistler wrote:[pile size & moisture level] make me think that what he was doing was actually anaerobically digesting the wood as opposed to composting it.

I disagree!

His material was much woodier than most composting operations would favor, and that made all the difference.

Being maybe 50% wood, his raw material had stupendous loft. That is to say, the pieces were large enough and shaped in such a way as to maintain air channels, even when piled very deeply.

Similarly, wood is very absorbent, as the hugelkultur article points out.

Lastly, because much of the carbon isn't bioavailable at first, aerobic composting can continue on for much, much longer. He had to tailor the chip size distribution so that the bioavailable carbon balanced the nitrogen, but some reserve carbon would become available as the process continued.

As others have pointed out, most of the calories consumed by a pachyderm are consumed aerobically, and both Jean Pain and the animal system we're using as a model for it feature a contained chamber in which a limited amount of anaerobic fermentation is carried out for a particular purpose.

All that aside:

Have you looked at the New Alchemists' compost heated greenhouse idea? It resembles yours a lot, and I think your plan would work well, but it they found it very important to account for moisture, ammonia, and CO[sub]2[/sub] in the exhaust gasses. A soil filter seems to work well on this gas mix, and the system has extra benefits for plants growing in that filter.

I think a compost-heated greenhouse on the sun-facing wall of the house might work well: you could take advantage of solar gain as well as compost heat, and breathe air filtered by compost, then soil, then plant leaves, or leave the air in the greenhouse mostly separate and rely on heat passing into the house through the wall of the compost bin. Also, the space used for composting in winter could be cleaned out and opened up for other uses in warmer months.

This may be coming out of far left field, but... what about applying the anaerobic compost/digestion concept to a mortuary?

Sol wrote:
This may be coming out of far left field, but... what about applying the anaerobic compost/digestion concept to a mortuary?

My friend, a 3rd generation undertaker says bodies don't decay like they used to due to all the preservatives and other chem in our systems.  However, I am relatively certain that zombies are anaerobic.  Just let me get one thing straight, would these be mastadon zombies or human? 

yukkuri_kame wrote:
My friend, a 3rd generation undertaker says bodies don't decay like they used to due to all the preservatives and other chem in our systems.  However, I am relatively certain that zombies are anaerobic.  Just let me get one thing straight, would these be mastadon zombies or human? 

My friend, let me just give you the title to a zombie movie to beat all zombie movies:

[size=14pt]Night of the Zombie Grandmothers![/size]

joshthewhistler wrote:


I think you can tell what I'm getting at. Do you think it would be possible to recreate conditions similar to those of a mastodon's gut to produce heat, methane and digested woody products?

These conditions would be:
-a large chamber.
-kept relatively warm until it produces its own heat.
-filled with a mixture of water, chipped woody products and bacteria.

What I imagine is a tank integrated into a house instead of a woodstove... Ambitious, maybe too much so.

Note in particular, that this is anaerobic decomposition (fermentation) taking place. This differs from most composting methods.

This is just something that's been on my mind for a while after reading Tim Flannery's book, The Eternal Frontier, where he advocates the re-introduction of megafauna into the North American biome. Worth reading...

Just thinking out side the box here, but this "could" be worth looking at for someone also into alternative house building.  Why not a "chute" for lack of better terminology here at the moment in a kitchen where the family drops the compostable waste product into a metal 4 sided bin on the other end that can capture the heat of the composter and the composted soil is slowly removable on the outside via a screened lid or something?  Waste water from the kitchen can also feed the water requirements of the composter. 


I need more coffee.