Generation of biogas from coffee-pulp and cow-dung co-digestion: Infrared studies of postcombustion emissions

Biogas could be produced by the co-digestion of coffee-pulp and cow-dung mixture under solar radiation. Gas chromatography and FTIR spectroscopy were used to analyze the chemical compositions of the generated biogas and its postcombustion emissions. From the first month of co-digestion at mesophylic conditions, methane content in the biogas attains 50% of the yield. This content increased up to 60% and remained almost constant for at least 8 months of further digestion. The FTIR gas spectroscopy analysis revealed the presence of over 70 chemical compounds in the biogas generated after 4 months of co-digestion along with several compounds hazardous to environment and animal health like isocyanic acid, and bromomethane. Combustion emission of the biogas contained several components like CH4, C3H8, CO, SO2, HI, and probably Br2 which are strongly harmful to human and animal health. Results presented in this work indicate that if the biogas is to be considered as a fuel, the conventional combustion technology has to be upgraded to prevent these hazardous emissions to the atmosphere.