Biodigesters are living things, and just like a vegetable garden or flock of chickens, they require regular maintenance to function properly. It’s important to avoid adding materials that can overwhelm or clog up the digester, including wood or plant stalks thicker than your finger; large amounts of meat; bones (unless they are ground up); fresh citrus or apples; and fresh chicken manure (which is OK only if it’s allowed to dry first). A few 5-gallon buckets of digested slurry will need to be removed every few days for a 700-gallon digester like the one at Maitreya, but otherwise the digester shouldn’t ever need to be cleaned out.
Regular use of the gas is important to avoid explosion hazards. Letting the digester sit for more than a week can create an abundance of biogas. Operating the digester at its natural pressure, without further gas pumps to pressurize it, in addition to the appropriate check- and pressure-relief valves, helps ensure that an unsafe buildup of gas doesn’t occur.
A biodigester of this size should be cleared with your local fire marshal, who may or may not be sympathetic to its construction. Biodigesters are not common in North America, and some education of officials will likely be required. Warren has been working with the City of Eugene for formal approval, and the case is pending.