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The following is a statement from the Appropriate Infrastructure Development Group (AIDG) about biodigesters and how they work:
"Unlike a septic tank, which is not sealed and vents methane, as well as passing ef- fluent to its leach field, a biodigester is a sealed system that intentionally promotes the controlled buildup of methane. As methane builds up in the chamber, it in- creases to a level that kills parasites and cysts. More waste is added to the cham- ber and is slowly consumed and sterilized by the . . . bacteria. As time passes, this sterilized effluent builds and flows through the exit of the chamber. This former fecal matter is now a nearly sterile fertilizer, suitable for use on [food] crops. The ex- cess methane . . . is piped away from the chamber and stored for use in heating, cooking, [and] lighting. . . .".
AIDG's design uses polypropelene plastic bags and plastic tubing to remove the methane from the biodigester. AIDG claims that their "family-sized" biodigesters can generate up to four hours of energy for cooking or water heating.
- Van Horn, R. (2007). Green and Non-Electric Technology. Phi Delta Kappan, 88(8), 630-631.