Economic and energy evaluation of mowing, harvesting and logistic solutions for the recovery of grass residues from non-cultivated areas for biogas feeding

The increasing demand of biomass for biogas production is arousing some concerns about the sustainability of this process. In fact, the cultivation of energy crops in farmlands is becoming more noticeable, causing a competition with food production. The utilisation of grass from the management of territory as a feedstock for the anaerobic digestion process could contribute to reduce these problems, both on environmental and social aspects. In fact, grass exploitation, beyond minimize the competition with food, could reduce eutrophication and production of greenhouse gases, provide nutrients for the fertilization of the soils and make more profitable the management of landscape and the biogas production. Although currently grass is not used in the biogas production chain, it is a widely available biomass within the territory. Its anaerobic digestion appears feasible from a functional point of view; nevertheless, there are still few studies related to economic, energy and environmental recovery of this biomass, considering non-cultivated green areas. The PhD project will investigate about the feasibility of exploitation of grass collected in non-cultivated areas for biogas production, examining: - the available biomass of grass for the anaerobic digestion according to the Veneto region territory; - the best systems for the supply of anaerobic digestion plants; - the biochemical methane potential of grass from non-cultivated areas; - the economic, energetic and environmental advantages or disadvantages of its exploitation. The results obtained until now reveal different solutions for the cutting, harvesting, transport and storing of grass collected along watercourses. From an economic and energy point of view, the costs are relatively high and variable depending on the organization of the harvesting system, the distances and the transport density. However, several environmental, social advantages, and a better hydraulic safety that the grass harvesting encompasses may be able to compensate the weaknesses encountered.