Sustainability of biorefinery systems. Evaluation of biofuel productions by means of emergy and LCA.

The present dissertation is focused on the feasibility and sustainability study of biorefinery systems, to be implemented by using bioresidues and biowaste produced by agriculture and food-processing industry. Such energy productions represent an opportunity for developing countries that have a large availability of biomass resources (e.g. African countries) and most of all they contribute to meet the need of replacing fossil fuels with alternative energy sources (i.e. biofuels). To this end the present work has explored hypothetical biofuel productions in the African continent from a sustainability standpoint, by adopting two environmental accounting methods such as emergy and life cycle assessment. The joint adoption of these two methodologies has been fundamental in order to provide a whole and complementary picture about the sustainability of the systems under study. First of all some methodological aspects have been clarified with regard to the application of emergy to the different generation of biofuels, providing helpful guidelines for researchers and not-specialists as well that want to deal with emergy evaluation of biofuels. At the same time an innovative way to represent graphically emergy results has been developed. This representation is based on the principle of polar coordinates and it shows simultaneously quantitative and qualitative aspects of emergy outcomes. Biofuel production chains have been evaluated on the basis of the different feasible biowastes that can be used to implement biorefinery systems (i.e. sugar and nutrient rich feedstocks). According to an emergy perspective, feedstocks like cassava peels and manure from grazing cattle proved to be the most promising biowaste in terms of potential production of biofuels and fertilizers, respectively. With regard to the transformation phase of biowaste into final sustainable products, LCA outcomes have shown that lignocellulosic-based feedstock (i.e. corn stover) generates higher environmental burdens against starch-based feedstock (i.e. cassava peels), because of the higher energy requirement for treating biomass to make cellulose and hemicellulose accessible for the subsequent enzymatic hydrolysis. In order to diminish the impacts of the by-products in output from biorefineries, part of the research has regarded the evaluation of the synergy that can be established between industrial and ecological systems, evaluating the ecosystems services provided by the latter as alternative to conventional solutions for treating plant emissions and waste production. From a methodological viewpoint this part of the study has explored the possible support that emergy can provide to improve and interpret the so-called techno-ecological synergy framework (i.e. TES).