Life cycle assessment of bio-based ethanol produced from different agricultural feedstocks

Abstract

Purpose Bio-based products are often considered sustainable due to their renewable nature. However, the environmental performance of products needs to be assessed considering a life cycle perspective to get a complete picture of potential benefits and trade-offs. We present a life cycle assessment of the global commodity ethanol, produced from different feedstock and geographical origin. The aim is to understand the main drivers for environmental impacts in the production of bio-based ethanol as well as its relative performance compared to a fossil-based alternative. Methods Ethanol production is assessed from cradle to gate; furthermore, end-of-life emissions are also included in order to allow a full comparison of greenhouse gas (GHG) emissions, assuming degradation of ethanol once emitted to air from household and personal care products. The functional unit is 1k g ethanol, produced from maize grain in USA, maizestover in USA, sugarcane in North-East of Brazil andCentre-South of Brazil, and sugar beet and wheat in France. As a reference, ethanol produced from fossil ethylene in Western Europe is used. Six impact categoriesfromthe ReCiPe assessment methodareconsidered,alongwithsevennovelimpactcategorieson biodiversity and ecosystem services (BES). Resultsand discussion GHG emissions per kilogram bio-based ethanol range from 0.7 to 1.5 kg CO2eq per kg ethanol and from 1.3to2kgper kg if emissions at end-of-life are included. Fossilbased ethanol involves GHG emissions of 1.3 kg CO2 eq per kg from cradle-to-gate and 3.7 kg CO2 eq per kg if end-of-life is included. Maize stover in USA and sugar beet in France have the lowest impact from a GHG perspective, although when other impact categories are considered trade-offs are encountered. BES impact indicators show a clear preference for fossil-based ethanol. The sensitivity analyses showed how certain methodological choices (allocation rules, land use change accounting, land use biomes), as well as some scenario choices (sugarcane harvest method, maize drying) affect the environmental performance of bio-based ethanol. Also, the uncertainty assessment showed that results for the bio-based alternatives often overlap, making it difficult to tell whether they are significantly different. Conclusions Bio-basedethanol appearsasapreferableoption from a GHG perspective, but when other impacts are considered, especially those related to land use, fossil-based ethanol is preferable. A key methodological aspect that remains to be harmonisedisthequantificationoflandusechange,whichhas an outstanding influence in the results, especially on GHG emissions.