Current limits of life cycle assessment framework in evaluating environmental sustainability – case of two evolving biofuel technologies

Highlights

• Can sustainability of forest and algae biodiesel production be estimated with LCA?

• Focus is on resource depletion, land use, water use, soil quality and biodiversity.

• Climate impacts are quantified to exemplify the uncertainty of the results.

• Decision making related to biofuels is challenging due to uncertainties in results.

• The methods for assessing environmental impacts by LCA still need to be developed.

Abstract

The growing need to use biofuel raw materials that do not compete with food and feed have resulted in a growing interest in lignocellulosic materials and microalgae. However, the life cycle environmental benefits of both biofuels have been questioned. The aim of this study was to evaluate how environmental sustainability of forest-based and microalgae biodiesel can be estimated by using the life cycle assessment framework. These biofuel chains were chosen because they are contrasting systems, as the first one is based on a “natural” feedstock production system, while the second one is an entirely anthropogenic system using an artificial infrastructure and external inputs to grow microalgae. This study focuses on life cycle impact categories still under methodological development, namely resource depletion, land use and land use change, water use, soil quality impacts and biodiversity. In addition, climate impacts were quantified in order to exemplify the uncertainty of the results and the complexity of estimating the parameters. This study demonstrates the difficulty to assess the absolute range of the total environmental impacts of the two systems. The results propose that the greenhouse gas emissions of microalgae biodiesel are higher than those of forest residue-based biodiesel, but the results of the microalgae chain are very uncertain due to the early development stage of the technology, and due to assumptions made concerning the electricity mix. On the other hand, the microalgae system has other advantages such as low competition on productive land and low biodiversity impacts. The findings help to recognise the main characteristics of the two production chains, and the main remaining research issues on bioenergy assessment along with the methodological development needs of life cycle approaches.

Introduction

In order to mitigate climate change and reduce dependency on fossil fuels, ambitious targets have been set for the use of renewable energy in transportation. For example, the European Union (EU) has set a 10% target for renewable energy in transport by 2020 in the EU Directive (28/2009/EC) on the promotion of the use of energy from renewable sources (RED). Also, the United States and many other countries have set ambitious targets for biofuel production (EISA, 2007; IEA, 2010). Along with growing global population, changing dietary preferences, and increasing use of biomass for other industrial applications, the use of biomass is expected to increase and cause competition for biomass resources (Berndes and Hansson, 2007). To produce biofuels, a wide range of biomass sources with various conversion routes can be utilised. Some biomass production systems are almost natural, such as forests, and some are to a large extent anthropogenic, such as microalgae production. In general, the anthropogenic systems use more inputs (fertilisers, pesticides, energy and water), but the productivity per hectare is high (Lardon et al., 2009).

The ambitious targets to increase biofuel production have created pressure to assess the environmental and social impacts of the expanding bioenergy production. Many studies have shown that first generation biofuels can cause even more environmental impacts than their fossil counterparts, and often second generation biofuels based on lignocellulosic or waste biomass are considered a potential solution to more sustainable biofuels production (e.g. Fargione et al., 2008; Gonzalez-Garcia et al., 2009). However, there can be significant problems in the sustainability of second generation biofuels as well (Melamu and Von Blottniz, 2011). These challenges of the input flows can be mitigated by various eco-design strategies using recycled materials from industrial sources (Soratana and Landis, 2011; Kadam, 2002), by aiming at reducing output fluxes to the environment, and/or by recycling them in system loops.

The studies on the environmental sustainability of biofuels are often based on life cycle assessment (LCA) (ISO, 2006) or an application of it. To ensure the sustainability of the biofuels, the EU has established a set of sustainability criteria for transportation biofuels and other bioliquids in the RED. The RED methodology for GHG impacts assessment is an application of LCA, as it aims to consider the impacts during the whole life cycle of biofuels. However, several problems of bioenergy LCA studies related to the use of input data, functional units, allocation methods, reference systems and other assumptions have been identified (Cherubini and Strømman, 2011). In addition, uncertainties and use of specific local factors for indirect effects (such as land-use change) may result in significant variation in final results (Cherubini and Strømman, 2011; Soimakallio and Koponen, 2011; Soimakallio et al., 2009). Due to the lack of input data and the immature state of the assessment methodologies for some of the impact categories, environmental impacts other than climate change are not usually assessed (Cherubini and Strømman, 2011). These challenges make the comparisons of the LCA bioenergy studies complicated.

Despite the methodological difficulties in producing reliable and unbiased estimates of the impacts of alternative production systems, biofuel production is a rapidly increasing field due to pressures of climate change mitigation. Therefore, an important viewpoint is to consider the available sustainability assessments as an input to make as optimal decisions as possible, taking potential biases and uncertainties of the available information into account. Techniques developed to support LCA-based decision-making with respect to multiple criteria (e.g. Myllyviita et al., 2012) and uncertainty assessments (e.g. Mattila et al., 2012) can be utilised in this context.

The aim of this study is to evaluate how the environmental sustainability issues concerning forest and algae biodiesel production can be estimated by using the framework of life cycle assessment. The forest biodiesel system is based on a “natural” feedstock production, while the algae production is an entirely anthropogenic system using an artificial infrastructure and inputs. These two biofuel chains were chosen because they are contrasting systems, and therefore exemplify the current limits of the life cycle assessment framework effectively. A short review of the limitations of the current LCA methodology is performed, and the challenges related to the environmental assessment of the two systems are discussed. An example of the complexity of quantitative assessment is given concerning the GHG emissions. By assessing the two very different biofuel chains, the study illustrates the challenges related to decision-making, while the best possible biofuel products should be selected for future development.