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The use of agricultural residues for the production of bioenergy offers tantalising prospects of reduced pollution and greater food sovereignty. Integrated food and bioenergy systems seek to optimise the joint production of food and energy. Integrated food and bioenergy systems may be evaluated and compared with other food and energy systems using Environmental Sustainability Assessment (ESA).
This thesis investigates a range of integrated food and residuebased bioenergy production systems and provide methodological developments that are relevant for the assessment of such systems. The methodological developments concern distribution of environmental burden in multifunctional systems; consistent accounting of human labour inputs; and modelling of uncertainty regarding future conditions. Residue‐based bioenergy relies on feedstock from production systems that are multifunctional, which means that they provide several outputs. Environmental impact assessment of residue‐based bioenergy, therefore, involves the identification of relevant impacts occurring prior to the conversion of residues into bioenergy. Dividing the environmental burden of food production between food and crop residues to maintain a single‐product focus is a contentious practice, since no obvious allocation factor is available. In evaluations of bioenergy production systems that are based on residues from food production, it is recommended to expand the assessment’s system perspective to include food production and food outputs. Human labour is an indispensable input in all agricultural and bioenergy production activities evaluated in ESA. Assessment methods, however, differ with respect to accounting for human labour inputs. Emergy Assessment (EmA) routinely includes human labour inputs, but based on a variety of calculation approaches. The collection of methods referred to as LCA (Life Cycle Assessment) methods usually disregard human labour as a relevant input. It is suggested to adhere to a systematic approach to estimating the environmental impact of human labour inputs that is applicable in EmA and other ESAs. I recommend that human labour be accounted
in labour time, and that labour’s environmental impact be based on all inputs required for making labour available. Practices and technologies that are expected to be implemented several decades into the future and that are compared with existing alternatives should not solely be compared using current conditions. The evaluation of these systems must take into consideration that future conditions may be significantly different from current conditions. It is suggested to use explorative scenarios based on narratives of the future to emphasise and be transparent about the uncertainty involved with planning for the medium‐ to long‐term. Modelling parameters may be deduced from such scenarios, making it possible to calculate scenario‐dependent results. Applying the methodological developments above, two cases of integrated food and bioenergy production in Ghana are described. Crop residue‐based biogas production and nutrient cycling in a remote village was shown to be a viable alternative to wood fuel and synthetic fertiliser use, in spite of increased labour inputs. In future scenarios where materials are scarce and labour plentiful, the investigated biogas‐based and agroforestry technologies appear relatively more attractive. Fruit and cocoa residue‐based biogas production in a fruit processing facility, with return of compost to pineapple farmers also proved to be a viable technology. It is recommended that relevant stakeholders explore the implementation of biogas and nutrient recycling technologies in preparation of reduced access to existing energy and nutrient
sources. Primary contributions to the research field are suggested improvements to specific methods of evaluating integrated food and residue‐based bioenergy systems. Evaluation of such systems
requires an expanded system perspective that encompasses multiple outputs. It requires ways to properly account for labour, since energy and material input reductions, often associated with integration, result in increased labour inputs, as observed in the case studies. Evaluation also requires consideration of scenario uncertainty since implementation takes time and societal conditions may change significantly during the implementation phase. The contribution includes empirical data concerning farming and bioenergy conversion technologies in Ghana and a recommendation to
implement biogas and nutrient recycling practices.
Original languageEnglish
PublisherTechnical University of Denmark, Department of Chemical and Biochemical Engineering
Number of pages204
StatePublished - 2016
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