Teresa M. Mata, Antonio A. Martins, Subhas K. Sikdar, Carlos A. V. Costa, and Nidia S. Caetano

Abstract This chapter describes how to perform a sustainability evaluation of microalgae biodiesel through its supply chain. A framework for selecting sustain­ability indicators that take into account all three dimensions of sustainability: eco­nomic, societal and environmental, is presented. Special attention is given to a useful definition of the boundary for the system and to the identification of the rel­evant impacts associated with the biodiesel supply chain stages. A set of sustain­ability indicators is proposed for quantitative sustainability assessment, based on the impacts deemed relevant for each supply chain stage. Some qualitative arguments [10] [11]

are also presented to support the evaluation. Although microalgae appear to be superior in some respects to other currently used feedstocks, the development of large-scale microalgae production systems still needs further research.

1 Introduction

It is commonly accepted that our dependence on fossil fuel and the gradual rise of greenhouse gas (GHG) in the atmosphere are intimately coupled. Several strategies are being devised and currently implemented in the transportation sector of the economy to stem this GHG rise. Examples of Government and business strategies alike include the development of alternative fuels, more efficient engines or trans­portation means, transportation networks better fitted to the societal and economic needs of evolving human societies, among others. In the short term, biofuels, such as biodiesel or bioethanol, are seen as viable options to partially fulfill the objec­tives of reducing the environmental impacts, in particular of global warming.

Biodiesel has some important advantages over other currently sought potential solutions. It can be produced from a wide range of vegetable oils from agricultural crops (e. g. rapeseed, soy, sunflower, palm oil, hemp, among many others) or even residual materials, in particular animal fats from the meat or fish processing indus­tries that are difficult to dispose of. The technology and know-how needed to pro­duce it efficiently is already available, and setting up a production facility is relatively easy. The real challenge here is to have access to enough raw materials to meet the current demand, without compromising sustainable development. Although source-to-wheel assessments indicate that the use of biofuels in vehicles yields benefits in terms of GHG and other pollutant emissions (e. g. sulfur and nitrous oxides) when compared to petroleum-based fuels, their impact on the biodiversity loss and competition for arable land can be deleterious if general sustainability cri­teria are not met. Also, the precise amount of saved CO2 emissions depends on the feedstocks used, the production processes, and on several other factors.

Thus, it is fundamental that the emerging biofuels sector is built on sound sustain­ability principles. In that regard, the European Commission recently put forward a broad set of sustainability criteria for biofuels in the Directive 2009/28/EC [3] for the promotion of renewable energy sources, which complement the targets already defined by the European Union concerning the utilization of biofuels. Some of the sustainability criteria in this new directive include that no raw material should be provided from undisturbed forests with important biodiversity, no land with carbon stock (wetlands or continuously forested areas) should be converted for biofuels pro­duction, the use of land for the production of biofuels must not be allowed to com­pete with the use of land for the production of food, a minimum of 35% GHG savings has to be attained, and also, societal considerations must be taken into account.

However, the increase in production and even the announced targets for biodiesel has raised some problems of its own. Nowadays, vegetable oils (edible or non-edible) and animal fats are the main feedstock for biodiesel production. As vegetable oils are also used for human consumption, the competition for arable land and the expected increase in food prices have become significant concerns. Additionally, it increases the biodiesel production costs, hindering its usage, even if the environ­mental impact of biodiesel is smaller than that of fossil fuels. Production processes may not be most adequate and optimized for the available feedstocks. Also, to fulfill the EU target of 10% from domestic sources, the actual feedstocks supply and the domestic arable land available in Europe are not enough [17] . Moreover, extensive monoculture plantation, the conversion of high conservation-value forests, and other critical habitats for cultivation of biodiesel feedstocks are unacceptable. These habi­tats and associated biological diversity can be lost forever, due to the cutting of existing forests and the utilization of ecologically important areas [ 14] . Also of concern are jeopardizing food supplies of people living in developing countries that still strongly depend on agriculture.

Therefore, new feedstocks are needed to complement the existing ones. Examples include the utilization of agricultural crops not used for human consumption, such as lignocellulosic materials and microalgae, among others, with higher biomass productivity when compared with the currently used feedstocks [18]. All options have their specific advantages and drawbacks that have to be taken into account when selecting adequate feedstocks. As the majority of production processes asso­ciated with alternative feedstocks are still under development, decisions concerning their development and practical implementation should be made considering all three dimensions of sustainability: economic, societal and environmental.

Among the potential feedstocks, microalgae are increasingly seen as a viable option for the production of biodiesel and even other types of biofuels. This work attempts to evaluate the relative sustainability of microalgae biodiesel when com­pared with the currently used fuels, and to identify the key advantages and problems associated with their use for biodiesel production.