Anaerobic digestion of different feedstocks : Impact on energetic and environmental balances of biogas process

The possibility of limiting the global warming is strictly linked to the reduction of GHG emissions. Renewable energy both allows reducing emissions and permits to delay fossil fuel depletion. The anaerobic digestion of animal manure and energy crops is a promising way of reducing GHG emissions. In Italy agricultural biogas production was considerably increased; nowadays there are about 520 agricultural biogas plants. The increasing number of biogas plants, especially of those larger than 500 kWe (electrical power), involves a high consumption of energy crops, large transport distances of biomass and digestate and dif\ufb01culties on thermal energy valorization. In this study the energetic (CED) and environmental (GHG emissions) pro\ufb01les associated with the production of electricity derived from biogas have been identi\ufb01ed. Three biogas plants located in Northern Italy have been analyzed. The study has been carried out considering a cradle-to-grave perspective and thus, special attention has been paid on the feedstock production and biogas production process. The in\ufb02uences on the results taking into account different plant sizes and feeding rate has been assessed in detail. Energy analysis was performed using the Cumulative Energy Demand method (CED). The climate change was calculated for a 100-year time frame based on GHG emissions indicated as CO2 equivalents (eq) and de\ufb01ned by the IPCC (2006). In comparison to the fossil reference system, the electricity production using biogas saves GHG emissions from 0.188 to 1.193 kg CO2eq per kWhe. Electricity supply from biogas can also contribute to a considerable reduction of the use of fossil energy carriers (from 123.97 to 10.08 MJfossilper kWhe). The electricity production from biogas has a big potential for energy savings and reduction of GHG emissions. Ef\ufb01cient utilization of the cogenerated heat can substantially improve the GHG balance of electricity production from biogas