Application of Carbon Footprint to an agro-biogas supply chain in Southern Italy

Over the last few years, agro-biogas has been receiving great attention since it enables replacement of natural gas, thereby representing a tool which reduces greenhouse gas emissions and other environmental impacts. In this context, this paper is aimed at the application of the Carbon Footprint (CF) to an agrobiogas supply chain (SC) in Southern Italy, according to ISO/TS 14067:2013, so as to calculate the related 100-year Global Warming Potential (GWP100). The topic was addressed because agro-biogas SCs, though being acknowledged worldwide as sustainable ways to produce both electricity and heat, can be source of GHG emissions and therefore environmental assessments and improvements are needed. Additionally, the performed literature review highlighted deficiencies in PCF assessments, so this study could contribute to enriching the international knowledge on the environmental burdens associated with agro-biogas SCs. The analysis was conducted using a life-cycle approach, thus including in the assessment: functional unit choice, system border definition and inventory analysis development. The primary data needed was provided by a farm located in the province of Foggia (Apulia region in Southern Italy), already equipped with anaerobic digestion and cogeneration plant for biogas production and utilisation. Results from this study are in agreement with those found by some of the most relevant studies in the sector. Indeed, it was possible to observe that GWP100 was almost entirely due to cropland farming and, in particular, to the production of ammonium nitrate in the amount required for fertilisation. Furthermore, environmental credits were observed thanks to: carbon sequestration enabled by no-tillage practice; and avoided production of chemical fertiliser thanks to 50% organic farming. Based upon the results obtained, a sensitivity analysis was carried out, thus highlighting reduced environmental impacts if ammonium nitrate was replaced with urea. Finally, thanks to this study, all the target stakeholders will learn more about the input/output flows involved in the system analysed, the related environmental impacts and the improvements needed to reduce them. In this way, it could be possible to compare the analysed agro-biogas SC with others of equal functionality, and so to enable considerations to be made on the resulting similarities and differences in terms of methodological approach, inventory flows and environmental impact.