Envisioning the sustainability of bioenergy production from anaerobic digestion

Resumo

One of the main challenges of modern society is related to the provision of energy systems that cover its needs while preserving the environment. Accordingly, the European Union has set ambitious goals to foster the implementation of renewable energy, including the accomplishment of 20% renewable energy in the final gross energy consumption by 2020. With this scenario in mind, the diversification of technologies and resources for the production of renewable energy is mandatory. Biogas is being promoted as a sustainable form of energy since it shares the principles of circular economy by converting wastes into several valuable products such as energy, water and nutrients. Life Cycle Assessment (LCA) is considered an appropriate method for the quantification of the environmental consequences of biogas production. The objective of this doctoral thesis was to examine the environmental sustainability of different biogas systems in the European Union and to evaluate their suitability in accordance with the European energy objectives, by applying the LCA methodology and other evaluation tools, such as Data Envelopment Analysis (DEA) and Analytic Hierarchy Process (AHP). Agricultural and sewage biogas systems were evaluated, including both well-established technologies and more innovative proposals. The environmental sustainability of agricultural biogas production was analysed in detail, from a life-cycle perspective. Initially, four Italian biogas plants digesting animal waste and energy corps at different ratios were compared with the aim of identifying the most polluting stages in which improvement options could be proposed. An additional analysis of two alternative plants was also carried out to evaluate the influence of substrate selection in biogas production, not only regarding its biogas potential, but also the amount and quality of the produced digestate. Finally, the eco-efficiency of 15 different biogas plants was determined, combining the LCA methodology with DEA. An innovative treatment system for the management of animal manure in Cyprus was assessed in the framework of the LiveWaste project (LIFE12ENV/CY/000544). The pilot plant, designed to perform the recovery and/or removal of nutrients from the anaerobic effluent, was analysed comparing four possible configurations. The potential environmental benefits of the implementation of the integrated system at full-scale were also evaluated in comparison with the most typical systems applied for animal waste in Cyprus. Finally, the AHP was applied to integrate economic, social and environmental indicators in the selection of the most sustainable waste management system in Cyprus. To conclude, different systems producing biogas from sewage were also analysed, including different treatment capacities in terms of population equivalent (PE). The potential environmental benefits of the co-digestion of food waste and sewage sludge in a wastewater treatment plant serving 150,000 PE was conducted to address legal barriers that hinder the development of more sustainable waste management options in the United Kingdom. Finally, an integrated treatment scheme was proposed for the co-management of sewage and domestic waste in a small and decentralised community of 2,000 PE. Several configurations that included the biological nutrients removal of the produced digestate were compared to identify the most sustainable one. Therefore, the work developed in this thesis provided remarkable evidence of environmental benefits and impacts in different biogas systems in the European Union with the objectives of i) improving conventional biogas production through the application of measures that reduce derived impacts of biogas plants, ii) promoting the implementation of innovative systems that integrates biogas production with digestate treatment and iii) identify methodological barriers in the application of LCA to biogas systems and discussion progress opportunities.