#methane digester

In my previous issues of Taking Care of Business I discussed how human feces can be composted aerobically in dry composting toilets, and also how flush-toilets can be made sustainable. Today I want to look at another alternative, the Methane Digester.

Methane? The greenhouse gas exacerbating climate change?

That's right. Letting organic matter decompose without the aid of oxygen produces methane, a flammable gas known for its distinct smell. We don't have to go too far to experience it, as this anaerobic decomposition may happen right in our bodies, where our intestines form an air-tight container to the decomposing organic matter. These farts that occasionally build up and escape in smelly clouds accompanied by the sound of the leather saxophone, are so benign that they're hardly worth the mention... in our species. (If it happens on a regular basis, there may be some digestion-related problem on hand. Otherwise you may laugh it off, or light it on fire for more laughs.)

In case of cattle, however, the emitted methane is more significant, due to their digestive mechanism, as well as larger sizes. Still, all the cows in the world are relatively low methane producers compared to the fossil fuel industry, especially with such innovative methods as fracking. And then there is the methane escaping from thawing permafrost, leaving huge craters behind. Since methane is a greenhouse gas, just like carbon-dioxide, this recently released result of ancient fermentation is both a cause and an effect of climate change.

image source

So How Can You Use This Gas?

By burning it, of course, just like propane, butane, or any other burnable gas. The idea is, if we are going to cook on a gas stove, it may as well be something that doesn't need to be mined from finite resources. Fermenting organic material in an oxygen-free space is not that hard, especially since our bodies already produce sufficient amounts of the needed raw material. It just needs to be fermented a bit further.

The Things I've Seen...

I have come across two impressive cases of methane digesters I'd like to present here. One is noteworthy for its simplicity, the other for its efficiency. Although both rely on animal rather than human excrement, the variability between these two examples suggests a lot of leeway for experimentation. The designer of one of these systems even said he could imagine it feasible to produce cooking gas for a high-rise apartment building, by fermenting the human wastes of its residents. Sounds exciting, though I still need to see such a system in action... But let me start introducing the simple digester:

The Best Thought-out Pig Sty

This setup was designed by a farmer, rancher, gardener, and tinkerer in Costa Rica. Even though he'd never even heard the term Permaculture, his design closes many loops beautifully. It's an ingenious way to combine corn, pigs, methane, and the kitchen stove.

I was quite amazed to see how clean the pig sty was. Of course, the guy pointed out, it gets cleaned three times a day, every time the pigs are fed. I first thought that was ridiculous, but he explained the reasons for this unusual practice. First of all, the pigs appreciate a clean floor (good for them). Also, it only takes about five minutes to hose down the slanted floor, and sweep all excrement with the uneaten corn-meal into the gutter on the lower end of the sty, so work wouldn't accumulate. Most importantly, though, he didn't want the pig excement to start fermenting in the open air.

All the slush washed into the gutter passed into a concrete basin, covered airtight by a black tarp. There it would sit, and be slowly decomposed by anaerobic bacteria, who as a byproduct generated methane. This gas stayed trapped under the black tarp, only a safety valve on top allowed excess pressure to escape. From there a pipe ran straight into the kitchen, where it was hooked up to a pair of burners. Using it was as simple as any gas stove.

The water that carried the material from the pigsty flowed through the digester, and came out as a brown colored, nutrient-rich effluent. This was further diluted with water and used to irrigate the corn, which eventually became pig-food. The circle was closed, the corn grew like crazy, the pigs enjoyed a clean sty and literally more food than they could eat, and nobody had to pay for the kitchen gas. Simple, easy, and at perfect scale. The family of six did most of their cooking that way, except for certain delicacies that required wood fire.

Efficiency in a Less Suitable Climate

Costa Rica, where temperatures are fairly stable all year round, even in the mountains, is the perfect place for this sort of setup. The digesting bacteria don't like sudden changes in temperature, which would affect their population, and thus their efficiency at fermenting. The other digester, however, was in the high desert of New Mexico, where outside temperatures would normally fluctuate between freezing at night and sweltering in the daytime. So how did its designer make it work? By thoroughly insulating it at night, and opening up the insulation to absorb the daytime heat. Also, he was living in an earthship-inspired home, which added to the temperature regulation.

The other thing about this amazing setup was that he hardly had any animals to produce fermentable material for him. About 10-15 chickens and a dog was all there was. A daily trip to the chicken coop provided a scooped dust-pan full of chicken manure, with ample feathers, straw, chaffs, and such bedding material. The latter part was important not only for its carbon-rich nature, but for the added surface area, which bacteria would populate. All this was washed down a modified garbage disposer, turning everything into a homogeneous slurry, and added into the digester. Unlike the owner of its Costa Rican counterpart, he didn't want to waste even a bit of excess gas. So with help of a compressor, powered by a wind turbine, the gas was concentrated into a big round container, previously used for storing propane. And of course, the effluent from this digester was also used to fertilize plants. Thus, he covered all the cooking needs of his 1-2 head household. Impressive for his location, and with only a dozen chickens!

Finally! An All-Electric Feed Truck, Powered Completely by Cow Poop

Make a Biogas Generator to Produce Your Own Natural Gas

For food waste, chop material into 1-inch or smaller bits. The author set up a chopping station in his garden using an old sink and garbage disposal attached to an extension cord. Other options include using a blender or chipper-shredder.

Make a Biogas Generator to Produce Your Own Natural Gas

Transform grass clippings, food waste and livestock manure into renewable biogas energy with a homemade biogas generator.

By Paul Scheckel

Your 747 is going down. There are no parachutes. Do you A) run into the cockpit, push the unconscious pilot to the side, and try to save the day, or B) accumulate as many seat cushions as possible and prepare for impact?

In the climate change world, Option A is reducing greenhouse gases to prevent climate change. Option B is accepting that change is coming and adapting to it. Thankfully, in real life the choices are not mutually exclusive, unlike the 747 scenario. I recently visited two farms that demonstrate the point.

Straus Family Farm focuses mainly on Option A. Overlooking Tomales Bay, this organic dairy has one of the first small-scale methane digesters. This device turns cow poop into power while eliminating planet-warming methane. This is a big deal because food systems account for about a third of planetary warming.

Meanwhile, Front Porch Farm is a farm focused mainly on Option B. A diverse, biodynamic bounty of wheat, exotic Italian livestock, rye, fruit trees, mulberry bushes and other products helps buffer Healdsburg-based Front Porch from the worst of climate change. What used to be a monoculture of wine grapes is now a variety of smaller plots that increases the farm’s resilience. Heavy rains, extended droughts, and other extreme weather that might decimate a monoculture crop are of less of concern with such a diverse system. 

In farm settings, many of the actions that reduce emissions (like installing a methane digester) also help buffer from the potential effects of climate change (by providing an income stream that offsets spikes in feed prices, for example). Conversely, rotating crops and incorporating organic material into the soil can boost a farm’s resilience while also pulling carbon from the atmosphere. As these practices are demonstrated successfully, more farmers will adopt them.