Comparative environmental and economic life cycle assessment of biogas production from perennial wild plant mixtures and maize (Zea mays L.) in southwest Germany

Abstract

Maize silage is the main biogas co‐substrate in Germany, but its use is often questioned due to negative environmental impacts. Perennial wild plant mixtures (WPM) are increasingly considered alternatives, as these extensive systems improve soil quality and enhance agrobiodiversity. Methane yields per hectare however do not match those of maize. This study examined whether the potential advantages of replacing maize with WPM for biogas production are counteracted by lower yields and associated effects. Life cycle assessment and life cycle cost assessment were used to compare the environmental and economic performance of electricity generation from WPM in two establishment procedures, ‘standard’ (WPM E1) and ‘under maize’ (WPM E2). These metrics were benchmarked against those of maize. The production of 1 kWh electricity was chosen as functional unit. The life cycle inventory of the agricultural phase was based on multi‐annual field trials in southwest Germany. Both WPM E1 and E2 had lower marine eutrophication and global warming potentials than maize. The GWP favourability was however sensitive to the assumptions made with regard to the amount and fate of carbon sequestered in the soil. WPM E1 performed less favourable than WPM E2. This was mainly due to lower yields, which could, in turn, result in potential indirect land use impacts. These impacts may outweigh the carbon sequestration benefits of WPM cultivation. Maize performed best in terms of economic costs, freshwater eutrophication, terrestrial acidification, fine particulate matter and ozone formation. We conclude that the widespread deployment of WPM systems on productive agricultural land should only take place if permanent soil carbon sequestration can be ensured. In either case, WPM cultivation could be a valid alternative for bioenergy buffers and marginal land where competitive yields of common crops cannot be guaranteed, but which could accommodate low‐input cultivation systems.

A parsimonious model for calculating the greenhouse gas emissions of miscanthus cultivation using current commercial practice in the United Kingdom

“…The most important is the amount of carbon sequestered during the cultivation period ( carbon_seq ). This can vary widely and greatly depends not only on site‐specific conditions (McCalmont et al, 2017) but also on the methodological approach selected for carbon accounting (Goglio et al, 2015) and the (assumed) permanence of the carbon sequestered (Lask, Martínez Guajardo, et al, 2020; Lask, Rukavina, et al, 2020). Due to the high variability in the possible values that this parameter can take, it is left to the user which value to select.…”

“…In recent years, industry's interest in miscanthus has grown due to its possible usage in a range of applications. It has been shown that miscanthus biomass can be used for the production of insulation material and chemicals, and can also serve as a bioenergy feedstock (Lask, Martínez Guajardo, et al, 2020; Lask, Rukavina, et al, 2020; Moll et al, 2020; Wagner et al, 2017). Each of these application pathways has been considered in environmental sustainability assessments, which commonly rely on the life cycle assessment (LCA) methodology (Kiesel et al, 2017; Lask et al, 2019; Wagner & Lewandowski, 2017; Wagner et al, 2019).…”

Conversion of biomass to biofuels and life cycle assessment: a review

“…The life cycle energy consumption and global warming potential of 1 MJ of gasoline and diesel production utilising switchgrass and pine residues were observed as 0.7 to 1.1 MJ and 43.2 to 76.6 g CO 2 eq, respectively Lask et al (2020) Global warming potential When considering land-use scenarios due to maize silage and wild energy crop production, blended feedstock consisting of both showed the lowest global warming potential as 198 kg CO 2 eq/kWh of electricity produced Mendecka et al (2020) Global warming, acidification, eutrophication and For treatment and upgrade of 1 kg of olive pomace, following impacts were observed freshwater ecotoxicity potentials Global warming potential = 0.468 to 1.024 kg CO 2 eq…”

Comparative life cycle assessment of bio‐based insulation materials: Environmental and economic performances

“…Both dLUC and iLUC can have highly influential effects on environmental performances, especially when considering an increased future demand for bio-based products. In fact, it was shown, for example, in a study evaluating different agricultural substrates for biogas production, that dLUC can decrease the total GWP up to 50% while iLUC can increase it by between approximately 16% and 31% (Lask et al, 2020). To minimize adverse effects from dLUC and iLUC, cultivation on marginal land should be prioritized where less or no competition with food crops is expected (Lewandowski et al, 2016).…”