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Complete Biogas: Food Waste and Biogas, Part 2

Feeding an ARTI-style digester with a floating gas holder

Cliff hanger, right? We told you there was a gold mine in back of your local restaurant in part one of this subject series (here), and we waved somewhere toward the direction of using the “found energy” tied up in the carbon bonds of that wasted food for this and that. (We mentioned cooking with that energy, for example.)

So the question is: How? How can we make the energy which is potentially available in food waste into usable energy? Let’s see….

In the developing world, many things happen at the village or household scale. If we cook our own meals using wood that we’ve gone into the forest and gathered, that is a system that has a household scale. (And it would please Thoreau, eh? Wood fire warms you twice, he said.)

But virtually all our systems in the US are industrial scale (that is, Big), including our energy systems (consider those long electric lines on towers marching along the freeway) and this includes the scale at which we waste food. Studies (such as this NRDC study) show that not quite half the food we produce in the US is thrown away.

From the NRDC study:

“Getting food from the farm to our fork eats up 10 percent of the total U.S. energy budget, uses 50 percent of U.S. land, and swallows 80 percent of all freshwater consumed in the United States. Yet 40 percent of food in the United States today goes uneaten. This not only means that Americans are throwing out the equivalent of $165 billion each year, but also that the uneaten food ends up rotting in landfills as the single largest component of U.S. municipal solid waste where it accounts for a large portion of U.S. methane emissions. Reducing food losses by just 15 percent would be enough food to feed more than 25 million Americans every year at a time when one in six Americans lack a secure supply of food….”

[Given the population of the US, ‘one in six Americans’ is about 50 million people.]

Now even given that almost all of our energy systems exist at an industrial scale, there are some circumstances where smaller scale energy production makes sense: a farm, a homestead; the kind of place you have now, or (since you are reading this) the kind of place you may want to have, someday soon. For those situations, a local energy system providing all or some of your energy may make sense.

And in planning for that local situation, your situation, one of the first things you need to consider is matching needs to energy sources. Wind can be a great source of (intermittent) electricity. Direct solar is also good for electricity (PV), for space heating and hot water. But cooking presents a modest challenge for those two common local energy sources. You can make a solar oven— it’s pretty easy, really— but (begging the forgiveness of the solar gods) most solar ovens are kind of bulky and clumsy, don’t you think?

So here’s a twist: how about using wasted food to supply all of your cooking needs, and to supplement your space heating, or even hot water supply?

And how can you do that? (Gee. Somehow biogas comes to mind….)

Homemade Biogas

The short story is:

Start with a container. It doesn’t have to be strong, but it has to hold liquid, and gas at very modest pressures. The container can be steel, concrete, plastic or made of any other suitable material, with few exceptions. (Toxic stuff is not good; the biogas biology is sensitive.)

Get some organic material, of the kind we might use in making a compost pile. (Not woody stuff, but almost anything else. Food waste makes great biogas.)

Keep it wet, keep it warm, keep it pH-balanced, and very shortly, by a process that is natural, very ancient, and which may seem a bit magical (hey presto!) a burnable gas— biogas, made almost entirely from methane and carbon dioxide— will bubble out. (And just to clarify: methane is the main molecule in natural gas, the fossil fuel that is getting so much press nowadays because of fracking. Biogas gives you methane without the fracking. And it can even shrink your carbon footprint.)

There’s nothing else that’s essential, although lot’s more can be said about it. It really does not get any simpler for any kind of renewable energy use, except maybe standing in the sun to get warm, or burning wood. (Or eating. Definitely eating.)

It really is simple. Honestly. In fact, would you like some free plans for building any of four of the most common kinds of digesters? Then visit the free plans for biogas digesters page on the Complete Biogas website….

Of course, what you get out of your digester will be determined by what you put in. It has to be sized properly— and again, again, again, kept warm— but all else being equal, the more you feed it, the more gas will be produced.

Realizing this, you may well want to ask: How much food waste should I put in the digester? And what size should that digester be so that I can cook my meals, and get light in the evening?

And booyah, while we’re at it: How about the holy grail of biogas? Can I run my car on biogas?

Well, friends…. That’s all going to be discussed in the next blog… Keep reading.

A biogas plant installed at a house in Coimbatore, Tamil Nadu. Photo: S. Siva Saravanan” Or one might say: Feeding an ARTI-style digester with a floating gas holder.

Source: The Hindu (newspaper), “Cost effective green fuel for the kitchen

9/8/2014 3:55:06 PM

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