ENERGY FROM ALGAE: GROWTH OPTIMIZATION AND ALGAE-TO-FUEL CONVERSION ROUTES

摘要

Microalgae are generally considered as a high-potential renewable biomass source towards thernproduction of energetically efficient and sustainable fuels. Optimization of the various steps in the algae-to-fuel chainrnis required in order to achieve this goal, and especially the algae culturing. An alternative culturing configuration, arnso-called Hybrid Culture System, has been tested in order to combine the low cost advantage and easy operation of anrnopen pond system with the high rate of control and higher productivity of a photobioreactor. Using this hybridrnsystem, the biomass productivity could be nearly doubled in comparison to the production of a single open pond. Inrnaddition, the effect of intrinsic growth parameters such as light intensity and nutrient concentration has been studiedrnto improve the understanding of the growth kinetics (which could be described by the Michaelis-Menten kinetics) ofrnthe algae species (Chlorella fusca) used in the development of the system. The light intensity experiments helped torndetermine important factors such as optimal light intensity and open pond depth for this type of algae. In combinationrnwith the nutrient concentration experiments (using NO_3~- and PO_4~(3-)) we could observe that in general, the lightrnintensity is the limiting factor for the systems studied. For the algae-to-fuel routes, two thermo-chemical methodsrnhave been tested and compared with a third one from previous work: solvent extraction, thermo-chemical liquefactionrnand supercritical water gasification, respectively. With the results obtained, it is shown that the algae are a versatilernrenewable resource for energy carriers, but important process development activities are still required.