Energy Systems and Technologies for the Coming Century ...

2.1 Key issuesDifferent algal strains perform differently, therefore it is essential to select strainscapable of growing in variety of wastewaters and producing feedstock for biofuels thatcan compete with biodiesel, biomethane and bioethanol in terms of land and water use,carbon sequestration and GHG emission savings, etc. Capability of algae to consumelarge amounts of CO 2 also makes it an attractive option as the process could be carbonneutral (Wang et al., 2008).Naturally, lipids accumulation increases under specific conditions, thus it is important tomaintain those factors that lead to accumulation of lipids in algae, like nutrients, CO 2concentration and sun light, etc. (Schenk et al., 2008). The best performing micro algaestrain can be obtained by screening of a wide range of naturally available isolates and theefficiency of those can be improved by selection, adaptation and genetic engineering(Singh et al., 2011a).The higher biomass yield with minimal operational cost and energy input is also achallenge to make algal biofuels as a sustainable biofuel. The operational cost andenergy input can be reduced by utilizing nutrients from wastewater and CO 2 fromindustrial flue gases and cultivating at area receiving bright sun shine for longer period.The quality of oil used for the production of biodiesel has a great impact on the qualityof the biodiesel produced. Genetic engineering of key enzymes in specific fatty acidproduction pathways within lipid biosynthesis is a promising target for the improvementof both quantity and quality of lipids. Algae have excellent potential for the geneticmodification of their lipid pathways. Any increase in photosynthetic efficiency willenhance downstream biofuels production as it drives the first stage of all biofuelsproduction processes (Schenk et al., 2008, Singh et al., 2011a).Bioreactor designs vary widely, but there is room for improvement to make systemssimple and cheap enough to be scaled while maintaining the higher productivity andcontrol over the culture than ponds allow. Clearly, an integrative approach where allnutrients are recycled and co-products are generated would be necessary for either pondsor bioreactors to be economic (Chisti, 2008), though this would be easier to achieve forbioreactors because of the greater control over them.Algal strains required physiological and biochemical adaptations for conditions of lowlight, including tightly stacked thylakoids and large light-harvesting antenna complexesthat allow them to effectively capture light energy. Optimizing stress conditions to obtainthe highest possible yields of lipids in the cells is very important to make it economicallyviable biofuel. Stimulated evolution is one option commonly used for bacteria and stressconditions can induce spontaneous mutation in cultivated strains. Selection of thesenatural mutants can improve production yields. Another option is to select wild localspecies that are already adapted to local growth conditions. Genetic modification (GM)is another option to improve production efficiency of algal strain. One current example isthe Algenol Company which is developing a strain of GM cyanobacteria capable ofproducing ethanol. Improved harvesting technologies are also needed. Lipid extractionprior to esterification is an area for further research. It would be an important advance ifmethods without drying or solvent extraction of the algae slurry could be developed as itwould significantly reduce the cost of biomass pre-treatment (Singh et al., 2011b).2.2 SustainabilityWorld Commission on Environment and Development defined the term ‘sustainability’as “the development that meets the needs of the present without compromising theability of future generations to meet their own needs” (UNCED, 1992). Sustainabilityassessment of products or technologies is normally seen as encompassing impacts inthree dimensions i.e. social, environmental, and economic (Elkington, 1998).Sustainability has become an unavoidable issue in all major planning and undertakingsthat involve future use of energy, water and other natural resources. The sustainability ofbiofuels production depends on the net energy gain fixed in the biofuels that depends onRisø International Energy Conference 2011 Proceedings Page 277