| dc.description.abstract | Microalgae are a promising feedstock for biodiesel production. To determine the future of biodiesel production from microalgae in the Netherlands the following question was asked: Which process to produce biodiesel from microalgae will be most suitable in the Netherlands, looking at stain selection, process technology and sustainability? This thesis focuses only on photoautotrophic microalgae grown in closed photo-bioreactors (PBRs) for the production of biodiesel in the Netherlands.
Multi criteria analysis (MCA) was used to determine the most suitable species by using the criteria: lipid productivity, nutrient usage, climatic suitability, content of valuable co-products and harvesting ease. Also for the process design (cultivation method & harvesting technique) an MCA was used with the criteria: land-use, construction costs, operational costs and efficiency. It turned out that Nannochloropsis gaditana cultivated in a vertical column PBR and harvested through filtration is the best option, although for larger microalgae species centrifugation is preferred.
The sustainability (minimizing environmental impacts and decreasing the depletion rate of fossil fuels) of the algae to biodiesel life-cycle was reviewed through a literature study focusing on: net energy rate (NER), greenhouse gas (GHG) balance, freshwater consumption, nutrient usage and co-product allocation. Microalgae cultivation inside a PBR, based on current PBR designs, is not sustainable due to elaborate PBR construction materials, PBR operation and high nutrient requirements. However, through process integration, biodiesel from microalgae can become a sustainable biofuel. Sea or wastewater should be used to provide nutrients while flue gas from power plants should provide CO2. The residual biomass should be used to generate electricity through anaerobic digestion, afterwards all the nutrients, and water, should be recycled. In the Netherlands a PBR would require additional heating, which should preferably be derived as waste heat from other industries. All these process integrations require more research before successful application.
Although the cultivation of microalgae has far higher productivities compared to other fuel crops, the cultivation (in PBRs) still requires large surface areas to give a substantial contribution to the Dutch policy goal of a 14% share renewable energy in 2020. This is however even a larger problem with 1st and 2nd generation biofuels indicating that microalgal biodiesel has a larger potential to become the biofuel from the future. The costs of 1 l microalgal biodiesel grown in a PBR are currently too high.
The Netherlands cannot become a large producer of microalgal biodiesel, mainly due to limitations in space. With higher productivities (l/ha/yr) some significant amounts for national consumption could possibly be commercial produced in a near future, although much research is needed especially within the field of genetic engineering and for the integration of sea/waste water and flue gas. The Netherlands could become a major consumer of microalgal biodiesel produced in other countries which have sufficient space and a better suitable climate. The Netherlands also do have the potential to become a source of knowledge for algae cultivation. To gain knowledge about algae cultivation the first PBRs should be focused on the production of valuable chemicals. | |
