A Proposed Sanitation and Methane Production System

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For the ordinary rural household, perhaps a more sanitary (and certainly more fragrant) approach than the Gotaas design is a batch-load system which we've described in the Natural Energy Workbook (published in 1974 and available for $3.95 from Visual Purple, Box 979, Berkeley, California 94701). Under this plan, waste is collected in a dry storage toilet (a 55-gallon drum with a seat mounted in the top) which can be installed indoors (Fig. 3). After each use, sawdust, ashes, or plain dirt is sprinkled into the barrel to absorb moisture which would otherwise cause odors and allow the growth of disease organisms. These materials also balance out the acidity of urine and create an essentially neutral condition when other organic matter is added later in the process.

The container is removed from use while less than a quarter full (another aid to odor control). Since the digester top and the toilet top are interchangeable parts (see Fig. 4), you simply detach the seat at this time and mount it on a clean barrel which you install in the bathroom.

No handling of raw excreta is involved in the batch-load process. Instead, the entire partly filled barrel is moved to the digestion area and placed in a solar-heated water trough. (See Fig. 5). Green kitchen garbage, garden clippings, animal manures, and even paper are then added to the container until it's three-quarters full. (It's important to include animal wastes to balance the carbon/nitrogen ratio. Chicken manure is particularly good for this purpose.) Next, the tank is topped with water . . . which can be left over from rinsing out the previous digester vat, washing diapers, bathing, or other cleaning. (Most such "gray water" is, however, sanitary enough to drain directly into the garden.) Finally, the drum is covered with an airtight lid and its contents are allowed to digest.

For at least the following month, the digester's temperature will have to be kept at a minimum of 90° F. This—like household heating and the warming of water—is a "low-grade" heat function for which we recommend the use of solar energy. It would be senseless to warm the tank by means of high-grade processed fuels . . . especially natural gas, which is, after all, mostly methane. The object of the generating process is to produce fuel, not to consume it.

The 55-gallon drum full of waste should yield between 500 and 1,000 cubic feet of methane (equal in power to 5-10 gallons of gasoline. In addition, the sludge left in the tank will be good, usable fertilizer. It won't, however, smell as fresh as aerobic (dry and aerated) compost, because of nitrogen compounds that remain in the residue rather than evaporating as they would in the presence of air.

In practice, then, you might consider pouring the anaerobically digested slurry onto a pile of leaves, animal bedding, twigs, or other dry cellulose material and allowing the mass to compost aerobically for a week or two before you add it to the garden. This approach may help you get official approval of your system (mainly for psychological reasons, because the finished fertilizer will no longer look or smell like sewage).

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