A comparative analysis of the environmental and economic performance of seaweed production and biorefinery systems were modelled within the project MAB3 (www.mab3.dk). A framework for integrated sustainability modelling of the circular economy of offshore seaweed production and biorefinery systems using excess aquatic nutrients and atmospheric CO2 emissions as a resource for biobased production is proposed. The seaweed production system was pilot tested at two Danish coastal areas achieving relatively low productivities of 1 to 2 ton dry weight seaweed per hectare. Biorefinery systems producing ethanol and proteins (EP) or biogas and fertilizers (BF) as main products were compared. Results show that seaweed cultivation and biorefinery systems contributes to mitigation of climate change as well as water quality restoration. Improvements in the productivity (cultivation technology) and product portfolio (processing and cascade utilization) are needed for a seaweed biorefinery industry to become economically viable.
The break-even point for the MAB3 EP biorefinery system is obtained by an increase in the seaweed productivity of a factor 2 to 4. Development of seaweed cultivation technology is ongoing and requires expanding the scale of production. Regarding the product portfolio, especially use of seaweed for pharmaceuticals and cosmetics will increase the profitability of the seaweed utilization compared to use for energy, feed and fertilizers.
There are not synergies between the economic and environmental performance of the modelled systems in all aspects. The revenue of the EP biorefinery system was higher than the revenue from BF system, while BF production delivered larger mitigation of climate change, i.e. GHG emission reductions. Mitigation of aquatic eutrophication was highest for the EP system. The welfare economic value of the services delivered by the seaweed cultivation and biorefinery systems ranges between 5 and 20% of the raw seaweed production costs.