Gaseous biofuels from waste: low environmental and toxicological impact with maximum benefit on the greenhouse effect

Biomethane, usable in existing natural gas engines, allows realization of vehicles with low environmental and toxicological impact, particularly suitable for urban area operation (fleets of cars, buses and trucks), also satisfying the incoming more stringent regulation limits. On site biomethane production, through anaerobic digestion or future gasification-methanization plants, will allow the problem of gas distribution to be overcome when a natural gas grid is not widely diffused. The capture and use of biomethane derived from the organic waste matter decomposition process allows a significant reduction of greenhouse gas emissions into the atmosphere. Biogas production plants represent an attractive way, alternative to simple composting, to reduce organic material landfill disposal, as required by the European Union. With reference to dedicated crops, biomethane represents the most efficient method of biomass utilization in comparison with other biofuels in the first generation category. In any case, the same problems of land use competition (especially food in developing countries) can derive from the low conversion efficiency of solar energy in biomass. A better approach is given by the second generation for the capacity to use almost all the parts of the vegetables, leaving the edible fraction for food employment. For this category the best results could also be obtained with biomethane allowing consequent lower land use competition. Improvements in hydrogen production from waste and biomass by dark fermentation and the connected possibility of direct production of methane/hydrogen mixtures could be another advantage thanks to the possibility of favouring gas engine development with higher efficiency and further decreasing emissions.