Anaerobic Treatment of Organic Wastes from Controlled Ecological Life Support Systems

This paper describes the results of a project involving an anaerobic digestion system used in treating the human and vegetative wastes from a Controlled Ecological Life Support System (CELSS). The anaerobic digester biologically breaks down the organic matter in the wastes into a mixture of methane gas and carbon dioxide, while significantly reducing the BOD(biological oxygen demand ) of the wastewater. A standard waste was formulated consisting of a mixture of swine waste (the surrogate for human feces and urine), green wastes (primarilly lettuce), and paper wastes. The equipment used for this project was a 2.7 cubic meter digester tank filled with plastic media and heated to an average temperature of 35°C. The digester was run over period of 200 days and loaded on the average of five days per week. The results over this test period showed a 94% reduction in BOD and a 98% reduction in suspended solids in the wastewater. Biogas production was approximately 1 cubic meter of biogas per kg of BOD added to the digester per day. This biogas contained an average of 62% methane. Tests were carried out at Lockheed in Sunnyvale to determine the effectiveness of the digester effluent as a growth medium for vegetables in a hydroponic growing system.