How to Generate Power from Garbage
(Page 11 of 12)
May/June 1970
By the Mother Earth News editors
EMPTYING AND RELOADING THE DIGESTER
RELATED CONTENT
Before a digester is emptied, the valve in the gas line should be closed and the petcock opened to let the remaining gas escape. The digesters are emptied by removing the cover and forking out the decomposed material. Special attention must be paid to not smoking, lighting matches, or creating sparks, which would ignite the gas in the digester when it is first opened. After the gas has been completely diluted with air there is no danger of ignition or explosion. When the digester tank has been emptied and only a little material remains, care should be taken to permit the gas generated by the remaining material to escape and not accumulate in the tank. The cover should be left off and air fanned into the tank before working inside it or reloading. A further word: Gas masks are of no value when working with this gas and care must be used, as it can be deadly if breathed.
About 5-10 cm 3 of digested humus, and about half the liquid, should be left in the digester to provide seeding for the next load. When three or more digesters are used, the liquid from a tank which is ready for emptying can be transferred to a tank which is loaded and ready to start digesting, to facilitate the development of conditions for gas production.
The digester is usually filled by forking manure and other materials from accumulated piles or from the stable. If the plant has three or more digesters, one can be left open for filling as the necessary materials accumulate, and digestion again started when the tank is loaded. In large installations it will be economical to convey the manure and wastes from the barn and dump them in an empty digester by means of a moving bucket on a tight cable or overhead rail. A crane-type frame and clam-shell-type bucket can be used to remove the material from the digester.
After the cover has been sealed to prevent entrance or escape of air, the operation is similar to that described for the initial starting of a digestion tank. The valve to the gas-holder is left closed and gas from the petcock is sampled daily to determine when gas production has again started. In the case of reloading a tank, gas production will start quite soon because of the digested humus and liquid which were left in the tank.
When removing humus from a digester (such as the one shown in Figures 4 and 5), which is more or less continuously operated, care should be taken to collect material from the bottom which has been reasonably decomposed and to avoid lowering the water level below the baffle seal. When night-soil is added to this type of installation and two digester compartments are used, the additions to a compartment should cease at least a month or more before it is emptied. If the latrine is combined with the digestion tank, this may be accomplished by providing latrines on both tanks which can be used alternately.
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