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. Ta p water was used to prepare the slurry. The methane percentage in the bioga s produced ranged from 57 to 65%. The produced methane gas was used as an e nergy source for heating water by direct burning and fuel for a piston engi ne to produce electricity for domestic use. Fluctuation of the ambient temp erature and using dry (non-fresh) wastes affected markedly the quantity of biogas produced and percentage of methane. Also, the results showed that bo th the biogas quantity and methane percentage increased as the ambient temp erature increased to the optimum temperature of about 35 degrees C. The res ults also showed that cattle manure is the best animal waste and olive prod uct waste is the best plant waste for methane production. Fermenting organi c waste and animal manure in particular resulted in an odorless fairly stab ilized organic matter which could be used as soil conditioner and therefore protect the environment from a major Source of pollution. The animal manur e, which is considered a source of pollution and disturbance in the environ ment, could be converted into a source of energy in farms nearby, especiall y 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. T he cost analysis comparing the biogas costs with those of the market availa ble 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.