This study focused on identifying various system boundaries and evaluating methods of estimating energy performance of biogas production. First, the output-input ratio method used for evaluating energy performance from the system boundaries was reviewed. Secondly, ways to assess the efficiency of biogas use and parasitic energy demand were investigated. Thirdly, an approach for comparing biogas production to other energy production methods was evaluated. Data from an existing biogas plant, located in Finland, was used for the evaluation of the methods. The results indicate that calculating and comparing the output-input ratios (Rpr1, Rpr2, Rut, Rpl and Rsy) can be used in evaluating the performance of biogas production system. In addition, the parasitic energy demand calculations (w) and the efficiency of utilizing produced biogas (η) provide detailed information on energy performance of the biogas plant. Furthermore, Rf and energy output in relation to total solid mass of feedstock (FO/TS) are useful in comparing biogas production with other energy recovery technologies. As a conclusion it is essential for the comparability of biogas plants that their energy performance would be calculated in a more consistent manner in the future.

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Waste oil management systems include processes such as generation, collection, recycling, and disposal and result in various environmental, economic, social, and regulatory impacts which complicate waste management analysis. In this paper, the waste oil management system in Finland is analysed using the systems thinking approach to identify the main system components and to describe the interactions between them. The results of analysing the Finnish system increase the understanding of the main factors affecting the performance of waste oil management. The outcome of this analysis can be adapted for the examination of similar systems. The waste oil management system analysis shows an increase in the performance: the waste oil collection rate within the official collection system has increased more than 30% during the last 6 years. The environmental performance of the treatment and recovery system have increased, taking into account the increase of the material recovery rate, more than 70% during the last 6 years.

Employing a life-cycle assessment approach, this paper studies greenhouse gas (GHG) emissions resulting from biomethane used as transportation fuel. It focuses on both GHG allocation methodologies and uncertainties regarding GHG emissions from biomethane. The goal is to calculate GHG emissions of two types of biomethane used in transportation: that produced from biowaste feedstock and that extracted from dedicated energy crop feedstocks. The effects of allocation methods used for digestate and those of other factors arising during the life cycle of biomethane are studied. The GHG emissions of biomethane produced from biowaste with digestate use are approximately 22 gCO2eq MJ–1; those of biomethane extracted from dedicated energy crops are 61 gCO2eq MJ–1. However, using the substitution method for digestate decreases biowaste emissions by 10 gCO2eq MJ–1 and dedicated energy crop emissions by 22 gCO2eq MJ–1. The highest emissions uncertainties are related to land use change, cultivation processes, digestate use, and technology selections in digestion and upgrading. Using technology with high energy consumption or methane leakages will significantly increase total emissions. On the other hand, use of renewable energy in processes is one option for decreasing total emissions. It appears that biomethane could be produced with lower emissions than previous studies have shown by optimizing production and implementing new technology. The utilization of digestate in replacing mineral fertilizers, resulting in additional GHG emission reductions, is a key issue which should be accorded more attention in the future. For one to achieve reliable results, factors related to biomethane production and allocation methods for digestate emissions should always be chosen on a case-by-case basis.