The use of a large variety of impact assessment methodologies can be potentially problem­atic if one wants to compare LCA studies. For instance, the comparison of the results of the "eutrophication" impact is not possible between the study of Kadam (2002) and the study of Brentner et al. (2011). In the first case, the methodology used is CML and the eutrophication impact is expressed in phosphate equivalent, whereas in the second publication the method­ology used is TRACI and the impact is expressed in nitrogen equivalent. Moreover, some studies do not precisely state the impact assessment methodology (Clarens et al., 2010, 2011).

A comparison of the LCA results of bioenergy production from microalgae with results for fossil fuels and other biofuels should be included. The strengths and weaknesses of this new kind of bioenergy production compared to fossil fuel or classical bioenergy production from biomass must be identified. Assessed impacts should include climate change and an energy balance, but impacts that have reduced the interest in first-generation biofuel (such as land use change occupation or impacts linked with the nitrogen flows or the use of chemical prod­ucts) and have motivated the abandonment of fossil fuel (ozone layer depletion or abiotic re­source depletion) should also be presented. A focus should also be made on the quantity and the quality of required water, since evaporation or water spray to cool the process could lead to drastic water consumption (Bechet et al., 2010, 2011).

13.5 CONCLUSION

This chapter presents a critical review of 15 publications about LCA and bioenergy produc­tion from microalgae. The review illustrated the variability of assumptions made about technological and environmental performance of the different processes involved in the pro­duction and transformation of algal biomass. The main conclusion of this analysis is that there is real difficulty in comparing the environmental burdens of the proposed setups, and there is now a need for clear guidelines to ensure that each new LCA study will consolidate the cur­rent knowledge. This is of key importance, since the objective of LCA works will more and more often consist of guiding the design of new biofuel production systems and prove that they lead to actual progress in terms of environmental impact. In this spirit, there is a clear gain for the LCA community to accept a set of rules and guidelines to make any new analysis comparable to the existing ones.

As a consequence, we have proposed some guidelines for the LCA to allow a clearer and sounder comparison between processes and to better estimate the potential and challenges of microalgae for biofuel production.

Acknowledgments

This chapter presents research results supported by the ANR-08-BIOE-011 Symbiose project. Authors P. Collet, A. Helias, and L. Lardon are members of the Environmental Life Cycle and Sustainability Assessment research group (ELSA; www. elsa-lca. org). They thank all the other members of ELSA for their advice.