Complete Biogas: Designing a Low-Cost, DIY, Biogas Digester for North America, Part 1

| 11/13/2014 9:27:00 AM

biogas digester

There are two things that are true about biogas. At least two. And I mean things at the core of biogas, down in its chambered, beating heart. The first is that biogas wants to happen. It wants to happen like plants want to grow, like fire wants to burn. And that force, that will to happen, has (at least) those two aspects: life, like the plants; and chemistry, like the fire. But the second thing about biogas is standing on the other side of town, on the other side of the lake, on the other side of the ocean. And that second thing is that as simple as biogas is, it’s just as true that biogas is complex, deep, unfathomable.

It’s not just that there’s a world inside that digester; there’s a universe. It’s symbiotic to the 42nd degree, seething, stochastic, and astonishing. It lives in the dark, underground part of the wheel of life, and to fully understand it (I don’t) requires math, physics, chemistry, engineering, biology, ecology, and agricultural sciences. And I left some out. Now these two poles of biogas bear on my present subject, which is— across this new series of blog posts— to show you the parts and pieces that make up the design of at least one low-cost digester made for US latitudes and realities, and to explain why they exist, what they are intended to do. (And to tell a few jokes too. Jokes are important.)

If you’ve been keeping up with your caffeine intake and you have clever hands, by the end of the series I think you’ll be able to build one, just from what I’m going to show you. For free. Just because I like your sister. (She’s great, after all. No offense, but you need a bit more work. Isn’t honesty really the best policy?) Right then: biogas is simple. Keep it wet, keep it warm, and keep it away from the air, and huzzah! Almost anything that was once alive will yield up the energy in its carbon bonds as lovely burnable methane, mixed into marvelous natural biogas. Like plants want to grow, and fire wants to burn, biogas wants to astonish you.

Of course, we both know that even though plants want to grow, it takes real skill and deep knowledge to grow healthy food, and to do it year after year while keeping the land in good heart, protecting the earth. And even though fire wants to burn, just because you have a book of matches does not mean that you can design a good wood stove, one that will provide warmth without smoke, do it with real efficiency, and throw off lovely warmth without crisping the cat if wanders near. I’m saying, in other words, that to really understand farm-fresh fruit, fireplaces, furniture, fingers or fusion (that little thing the sun does) requires some science. You’ve got to learn stuff. At the same time, drop a seed, strike a match: to grow a garden or build a fire is not all that complex. How hard is it to use satellite TV? How hard is it to design the satellite?

So it is with biogas and biogas digesters. Making biogas couldn’t be much simpler than it is. Making a properly-designed biogas digester is solidly somewhere toward the other end of the spectrum. Make a digester for a science fair? Easy. If you’ve got a something-or-other that keeps the air out and the water in, well sure, that’s a digester. And yes, it may well generate biogas. Some. OK, but there are two critical questions that divide real success from relative failure: 1) Can you demonstrate you’re getting what you should out, given what you’re putting in? And 2) can you keep the thing warm outside on a cold night, with minimal energy input? The problem is the same if you buy a digester. After all, there’s no Institute of Good Gaskeeping, and it may take quite a while before Consumer Reports turns its spotlight in a biogas direction. Is the digester you’re thinking of buying well-designed and worth its cost? Does it look good? Does that mean it works well?

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