The Compost-Powered Water Heater: An Early System

A few years ago I had the idea to try to learn as much as I could about sustainable & resilient practices as I could.

I was not well set up to learn about these things. I've never known much about any kind of technology. I've always been a renter of rooms & apartments, and never owned any property to experiment on, or land to grow food on. I also didn't have much of a science background to draw on for understanding.

So, my idea was to try to find good books that would cover in detail some specific ecological technology or practice, and build up from there, one at a time.

One book that kept showing up in my Amazon recommendations was Gaelan Brown's The Compost-Powered Water Heater.

Before that, I had looked into biochar stoves, (which produce heat while also making a kind of charcoal that can be used as building material or added to the soil as an amendment, either way in effect drawing down carbon from the atmosphere and sequestering it into our constructions or into the soil.)

Then it was composting toilet systems, which use the heat generated by the composting process to eliminate the pathogens in our wastes, and then decompose them into humus, which can be incorporated back into soils, to re-incorporate nutrients and increase fertility, and possibly increase the overall carbon content of our planet's soils.

So compost-powered water heaters seemed like a progression on the theme: if the composting process generates a fair amount of heat, normally dissipated into the surrounding air, is there a way to collect some of that energy and put it to use, replacing some fossil fuel combustion, at the same time making more compost?

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So, this series of posts will be mostly a book report on Gaelan Brown's compact & useful volume, augmented with information from some of the many youtube videos that people have made of their compost heat recovery projects.

I would like to dive right into the systems that Brown installed with the Compost Power Network at the time of the book's publication, but I wonder if it wouldn't be better to start with the two historical experimental projects described in the book, from 1970s France and 1980s Cape Cod, Massachusetts: these two early systems really sketched out the full potentials for the systems that evolved from their trials, the first type relying on circulating water to draw warmth from compost piles, and the second based on air pulled through hot compost, to supply heat to greenhouse beds & other applications.

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For many sustainable technologies, there often seems to be some independent-minded tinkerer at the outset, who saw the potentials of some avenue of development, and then applied themselves to working on the technology & to promoting the possibilities of that application to the world at large.

For compost heat recovery, that pioneer has to have been Jean Pain, the Swiss-born farmer and forester, who derived an astonishing range of energy streams from piles of decomposing woodchips.

Jean Pain had an organic farm in Southern France, who also worked as a forester. As a part of a program of the French government to help prevent fires, Pain was paid to clear brushwood from the woods nearby his farm. All this excess brushwood at his disposal, Pain wondered if he could make compost of it for his farm.

J. Pain & Wood Shredder

Compost requires oxygen, and regular wood chippers make wood-chips that become matted-down and water-logged. So Pain developed a chipper that shredded brushwood, creating a stringy texture that allows for oxygen to permeate all areas of a compost pile. (Pain's wood shredders are available in France to this day.)

When Pain had achieved a consistency of woodchip that allowed for oxygen to circulate through the pile without requiring the pile to be turned (while at the same time retaining enough moisture for the compost bacteria to remain active) he experimented with various ways of arranging his compost piles.

In the end, Pain settled on coiling water pipe throughout a cylindrical pile, circulating water through to absorb the warmth generated by the compost pile.

From his fairly large compost piles, Pain was able to produce around 18 months of hot water (140F) for all the domestic needs of his farmhouse. (This was in the temperate climate of Southern France. Later, Brown outlines the changes the Compost Power Network found essential for making these systems work in colder North American regions.)

At the centre of these piles, Pain placed a steel tank for 'biogas' production, so that the heat generated from the aerobic, thermophilic woodchip compost could support the anaerobic generation of combustible methane/natural gas.

For those unfamiliar with the biogas process, I think it can seem at first a little counter-intuitive: aren't we trying to reduce the production of methane, from landfills and the inner fermentation chambers of cattle and to minimize our combustion of natural gas? I'll try to outline the basics of biogas production here, as far as I understand it.

When we pile up organic materials, like food scraps, lawn clippings, wood chips, etc. and ensure that the materials get enough oxygen (by turning the piles, or by ensuring that air can flow through the pile, passively or by use of a fan) then oxygen-loving thermophilic bacteria come to dominate the pile, and the process largely avoids producing methane, which is good, as methane is about 30 times as potent a greenhouse gas as is carbon dioxide.

If, however, you take some of that organic material and let it decompose in the absence of oxygen, anaerobically, you can produce your own methane, basically the same substance us Manitobans often have piped into our furnaces and hot water tanks. So, in Jean Pain's system, he would take some of the partially decomposed woodchips and put them in the water-filled steel tank within his pile. The anaerobic bacteria need warm water, around 100F, which the warmth of the piles produces pretty perfectly, and would produce a steady stream of biogas for around 5 months, before the tanks would need to be refilled.

Of course, if you collect this methane/biogas, then it isn't being released into the atmosphere as a greenhouse gas. Pain piped a hose from the top of the steel tank to a series of series of tractor tire inner tube. Pretty ingeniously, the filled tire tubes provided the pressure to supply his oven with biogas for cooking. Pain also converted his vehicles and farm equipment to run off compressed natural gas, and set up a generator to produce his electricity from the biogas as well.

In terms of climate change effects, biogas/methane/natural gas (CH4, a compound of carbon and hydrogen) when burned produces carbon dioxide and water (CO2 and H2O). When it is fossil-fuel based natural gas we are burning, we are taking carbon that was deep within the ground and increasing the net amount of carbon in the atmosphere.

But when we combust biogas, the carbon we are releasing is the same carbon drawn from the air by plants & trees we are decomposing, so the process is likely carbon-neutral, so long as the land is regenerating this biomass that we've removed, drawing a similar amount of carbon dioxide down once again. Pain was for the most not cutting down mature trees, he (I gather) collecting up fallen wood, pruning, and clearing away new growth where it was coming in too dense, for fire-smarting purposes, and not returning to that woodland for several years, no clear-cutting involved.

And finally, in addition to the hot water, cooking fuel, vehicle fuel, and electricity he was deriving from his compost & biogas piles, Pain attempted to derive warm air for a greenhouse, but running stovepipe from building, through the pile and back again, with the difference between the cooler and warmer air setting up a convection current to circulate the heat.

Not sure what he was collecting here, but looks interesting.

Asides from the various techniques Jean Pain worked out for compost heat recovery, Gaelen Brown emphasizes two interesting claims that Pain made about his systems, that seem to have been supported by further research:

1. More energy can be derived from composting a pile of woodchips than from burning it.
   
   Brown says he was told by many "seemingly knowledgeable people, including college professors and engineers" that this was impossible. However, the experiments he carried out with the Compost Power Network "at least partially validated Jean Pain's claim in this regard."
   
   He gives some calculations in the book, comparing the BTUs generated by composting 20 cubic yards of woodchips and by burning that amount in a woodstove, and finds that they give very similar outputs, though one process leaves behind finished compost to fertilize the soil, while the other process leaves behind ash.
   
   "[M]ore research is underway, but in a nutshell: Microbial respiration and digestion seem to be more energy-abundant processes than combustion. Microbes are more efficient at turning food into energy than is a woodstove. That should not be hard to believe, in my opinion." (Brown, 14)
2. Nitrogen-rich compost can be made from composting carbon-rich woody materials.
   
   Composters usually aim for a balance of carbon and nitrogen in a pile. Carbon provides the food-energy for bacteria, while the nitrogen provides bacteria the building-blocks they need to compose their cellular structures. The goal is usually somewhere around 25-30 parts of carbon to 1 part nitrogen.
   
   
   
   Woodchips have something like a 400:1 carbon-to-nitrogen ratio, and Pain used only shredded brushwood in his piles, without adding any food scraps, manure, urine, etc. And yet he felt the finished compost had good levels of nitrogen in it. How was this possible?
   
   Pain hired Belgian soil scientists to test the humus produced from his piles, and apparently they found his claim to be correct. The idea Jean Pain and others after him have had, is that "the aerobic respiration of the microbes composting a purely woody material actually pulls in nitrogen from the air and fixes it into the humus." (Brown, 21)
   
   This claim is intriguing. As I understand it, the vast majority of the nitrogen in our food system is synthetic, created by the energy intensive Haber-Bosch process, which uses high temperatures and high pressures to fix nitrogen from the air into fertilizer.
   
   
   The process was a key to feeding the population growth of the 'Green Revolution'; apparently 80% of the nitrogen in our bodies was created by this process. (Michael Pollan's The Omnivore's Dilemma has a fascinating section on this discovery and on the protean, brilliant, dark character of the German chemist Fritz Haber, who was also forerunner in the creation of chemical warfare.)
   
   But, synthetic nitrogen requires a lot of fossil fuels to produce and emits a lot of GHG, so many wonder about the long-term sustainability of this elemental process in the way we feed ourselves. Much has been said about the ability of legume plants to fix nitrogen in the soil. Could the microbial respiration of thermophilic bacteria feeding on decomposing wood be another organic method of transferring nitrogen from the air to the ground?

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Pain died young, before his time, passing away in 1981 from cancer at 51 years of age. His family established the Jean Pain Institute to conduct research & education programs, and to promote and refine the innovations Pain developed.

Very little was made of Pain's work over the 80's and 90's. It took until the 2000's for permaculture practitioners and others involved in sustainability & alternative energy to renew an interest in his work.

One of the few people who kept this avenue of appropriate technology alive in the intervening decades was Bruce Fulford, who designed an experimental compost-heated greenhouse, as a part of the New Alchemy Institute, on Cape Cod, MA.

I'll make that project the subject of my next post on compost heat recovery systems. The New Alchemy greenhouse is interesting, as the greenhouse operated in a colder climate than Pain's, and kept the composting materials indoors, within the building that required the heat from the compost.  And instead of coiled water pipes within the compost pile, Fulford used blown air as the heat transfer medium. This has advantages, with much less heat loss, but with the gases produced by compost having to be dealt with, in very clever ways that increase the sustainability of the operation.

Jean Pain Committee International, Belgium

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If anyone is interested in more youtube videos on the subject...

- Gaelen Brown lays out pretty much all of the content he has included in his book, for this Living Web Farms video: https://www.youtube.com/watch?v=cvMi6hgfcnw&t=136s

- A German documentary made during Jean Pain's lifetime. I've read people refer to this as being 'low-quality', but I personally love the historical quality of the film. Like the old CBC documentaries, I think the rough quality of the production gives one a better feel for how things were back then.
Part One: https://www.youtube.com/watch?v=JHRvwNJRNag&t=54s
Part Two: https://www.youtube.com/watch?v=zGCj7NA0OIs