Evaluation of the energy and greenhouse gases impacts of grass harvested on riverbanks for feeding anaerobic digestion plants

More sustainable scenarios in the bioenergy sector can be achieved when biomass exploitation is based on eco-efficient supply chains. Regarding this, grass as a by-product obtained from landscape management could provide a large quantity of biomass potentially utilizable in the Anaerobic Digestion (AD) supply chain. This study assessed the energy and greenhouse gases (GHG) impacts of grass obtained from the landscape management of riverbanks. A study area of a land reclamation authority was investigated by interpreting high resolution spatial data and determination of the biomass yield. In addition, an inventory was made of the grass production chain. An energy analysis was performed using the Cumulative Energy Demand method (CED), while the GHG balance of grass AD was calculated based on CO2 equivalents. Special attention was also given to the logistic approaches: two different supply systems were evaluated in order to determine the best supply chain for this feedstock. The results show that the biomass yield of riverbank grass amounts to 13 t (f.m)/ha (4.8 t (d,m)/ha) while the energy utilization of grass determines a saving on fossil energy of about 2.6-2.4 GJ/t (f.m). (7.0-6.4 GJ/t (dm).) and on GHG equivalent emissions of about 86-67 kg(CO2eq)/t (f.m) (233-181 kg(CO2EQ)/t (d m).) depending on supply distance and logistic approach. In this regard, the Indirect Logistic Approach (ILA) achieves the best performance in terms of the reduction of fossil energy and GHG emissions. The results suggest positive prospects for the integration of grass from non-cultivated areas into the AD supply chain in order to mitigate the requirement for agricultural feedstock and obtain a positive return, in terms of energy and emissions saved, from landscape management operations. (C) 2017 Elsevier Ltd. All rights reserved.