The Macroalgae-Based Biorefinery - a comprehensive review and a prospective study of future macroalgae-based biorefinery systems

Abstract

In this thesis the macroalgae-based biorefinery is studied from an environmental and economic perspective. Macroalgae (or seaweed) could function as an interesting third-generation feedstock for the production of biofuels and chemical products. There is no need for arable land or freshwater during cultivation, in contrast to first-generation biofuels. Macroalgae is currently mainly cultivated for food production. The production of macroalgae-based biofuels alone is not economical feasible. Therefore, the biorefinery concept will be studied. By combining both fuels with higher-value compounds, the system could become profitable. The first part of the thesis consists of a review of macroalgae genera, cultivation methods, products, production methods and the design of the systems. In the second part of the thesis, the biorefinery concept is tested on the basis of three case-studies. In these cases, different species and scenarios will be studied from an environmental and economic perspective and a sensitivity analysis will be performed. In case-study 1 the brown seaweed Saccharina latissima is cultivated in order to produce alginate, biogas and compost in a biorefinery. In case-study 2 Ulva lactuca (green seaweed) is cultivated for the production of ulvan, biogas and compost. In case-study 3 Ulva lactuca is collected and will be subject to ABE fermentation (the production of acetone, butanol and ethanol).

Both the life-cycle analysis (LCA) and the economic analysis are founded on many assumptions, which increased the degree of uncertainty for the results. The LCA for the impact categories global warming potential, non-renewable and renewable energy use does not show positive results for the case-studies. Especially case-study 1 performed poor, which is mainly caused by the energy-intensive alginate extraction process . Case-study 3 performed much better, but the separation of the products caused the impact categories to remain high. The economic analysis resulted in very positive values for case-study 1. Case-study 2 and 3 did not perform well. The sensitivity analysis showed that the impact of the assumed yield for the alginate and ulvan has a large influence on the economic feasibility of the system.

There is a need for further research in order to design case-studies with more accurate results. The lack of pilot plant data and well-founded calculations made the environmental and economic analysis complicated to perform. The use of macroalgae for the production of chemicals and fuels could be very relevant in the future. Before this will happen there are many remaining barriers to take, mainly with regard to the cultivation and conversion of the biomass.