How to Make a Home Biogas Digester (Maybe)

Enlarge Image Image Gallery Environmentalists are turning to biogas as a means to help farmers stop the flow of runoff into rivers and to make power and fertilizer in a green way. iStockphoto.com/Bob Ingelhart

Making methane cooking gas from waste and compost isn’t new. Tinkerers in remote locations and farms around the world have been tapping into biogas for years with varying degrees of success. The natural gas produced can be enough to provide cooking fuel, heat, hot water and even gas for specially modified vehicles. If you can make a home biogas digester yourself, you might have the world by the tail.

Environmentalists are turning to biogas as a means to help farmers stop the flow of runoff into rivers and to make power and fertilizer in a green way. But while YouTube clips abound with biogas success videos, few of them originate in the United States. 

Biogas production is a tricky business dependent on keeping temperamental micro-organisms alive and in perfect balance to keep the gas flowing. Also, U.S. codes for gas storage and sanitation are stricter for such endeavors. For many Americans, the process just isn’t cost-effective enough to make it worthwhile.

But for the tinkerer at heart, biogas can be a good challenge, says Bob Crosby, a research and energy management consultant based in Willow, Alaska.

“It’s a practical thing for people who might have a couple of animals or want to do it for the love of it,” he says. “To get a working system in place really takes some dedication.”

In a home biogas digester, anaerobic bacteria (bacteria that thrive in an oxygen-free environment) decompose organic matter into methane, carbon dioxide and sludge. In the first stage, acidogens (acid-producing bacteria) break down the raw waste into simple fatty acids. In the second stage, methanogens (methane-producing bacteria) consume the acids and produce biogas as a byproduct. Acidogens are hardier critters than methanogens, which makes biogas production never a sure thing. The trick is that the two organisms must be in balance, or else the pH balance of the system will kill off the critters.

Crosby is among the handful of biogas enthusiasts who spend their time perfecting digester designs and discussing improvements online. He believes that would-be home biogas digester constructors should build a tiny gallon-jug model before going all out with a small-scale or large-scale digester.

“This may be harder than you think,” he says.

Most biogas digester veterans, including Crosby, will say there are no guarantees with any biogas digester design. Temperature variables and microorganism health are the twin nemeses of digester operatives.

“They’re very fragile, finicky little bugs,” Crosby says.

But for those who can’t resist a challenge, Crosby shares with Grit the basics for a plan of a small-scale home biogas digester, designed to handle the flushes of a family of six. Look for information about these plans and a lively discussion of biogas construction online at www.Biorealis.com.