Evaluating variable organic waste to produce methane

Different animals' manure and residues of plants were tested and evaluated for methane (CH4) production. A cubical digester was constructed under the ground surface as a biogas generator using local construction materials. Tap water was used to prepare the slurry. The methane percentage in the biogas produced ranged from 57 to 65%. The produced methane gas was used as an energy source for heating water by direct burning and fuel for a piston engine to produce electricity for domestic use. Fluctuation of the ambient temperature and using dry (non-fresh) wastes affected markedly the quantity of biogas produced and percentage of methane. Also, the results showed that both the biogas quantity and methane percentage increased as the ambient temperature increased to the optimum temperature of about 35 degrees C. The results also showed that cattle manure is the best animal waste and olive product waste is the best plant waste for methane production. Fermenting organic waste and animal manure in particular resulted in an odorless fairly stabilized organic matter which could be used as soil conditioner and therefore protect the environment from a major Source of pollution. The animal manure, which is considered a source of pollution and disturbance in the environment, could be converted into a source of energy in farms nearby, especially those away from the national electricity grid. The results showed that a family of four to five persons living in the farm house can have sufficient source of energy by using such unit of 16 m(3) for cooking and lighting. The cost analysis comparing the biogas costs with those of the market available LPG bottles showed a pay back period of about 20 years, which suggests the non-feasibility of the units. Using such units in remote areas as oasis or mountainous farms will be highly valuable, especially in places lacking electrical connection. (C) 1999 Elsevier Science Ltd. All rights reserved.