Characterization of biogas generated in final disposal sites of urban solid wastes selected in the center zone of Mexico

Abstract

The results of the characterization of biogas generated in 13 final disposal sites of urban solid wastes in México showed uniform data relative to methane and carbon dioxide concentrations, with average values between 50% and 60% of CH4, and between 35% and 45% of CO2, in all sites, with slight ranges in percentage for each site. As regards nitrogen, its concentrations showed higher differences partly caused by the presence of air among the disposed wastes and elsewhere by probable differences in the waste composition, considering the original nitrogen content in the organic fraction. Oxygen concentration in the samples were very low and in several sites they fell below the equipment detection limit, which indicated that waste ages are higher than the necessary time to consume all the oxygen in the air trapped inside the cells, but, on the other hand, proved the insulation efficiency of the covering layers. As regards total methane and carbon dioxide emission —considering the biogas flows measured—it was found that sites with larger methane production are generally the larger producers of carbon dioxide. The results show trends that lead to the interpretation that the sites with larger greenhouse gas production are the oldest sites and/or are managed as sanitary landfills with sufficient compaction and appropriate covering of the disposed wastes. Nevertheless, equivalent CO2 emissions are considerably lower in sites were biogas is burned. Finally it was found that most of sanitary landfills have lower emissions of greenhouse gases, at least in relation to the size of the site and the quantity of the disposed wastes.