Methane concentration in biogas produced from dejections of milk goats fed with different diets

Due to its elevated methane content, resultant of the organic degradation in the absence of molecular oxygen, biogas is an attractive source of energy. The physical, chemical and biological characteristics of the manure are related to diet composition, which can influence the biogas composition. The objective of this work was to analyze the methane concentration in biogas produced from the substratum formulated with manure of milk goats fed with three different diets. Nine laboratorial digesters were used, installed in the Laboratory of Structures and Environment of the Department of Agricultural Engineering of Federal University of Vicosa City, Minas Gerais State, Brazil. The determination of the methane (CH₄) and carbon dioxide (CO₂) concentrations was carried out weekly in a Shimadzu 14B Chromatograph. The goats had been fed with three types of diets: grass, hay and ensilage. The substratum used on the anaerobic digestion process was composed by manure, inoculum and water, with final total solid concentration around 8%. The digesters had been installed inside of asbestos-cement box containing heated water enough to allow the substratum heating and control of the temperature on 30 °C. The gasometers had been confectioned with 4' PVC pipes, containing a graduated scale affixed on its external surface. The averages gas concentration in the produced biogas had been compared by the 5% probability level Tukey Test. It was verified that, it did not have significant difference between the treatments. The weekly average values of CH₄ concentration had been increasing during the process, varying between 61.8% and 88.15%.