Sustainability and life cycle assessment (LCA) of macroalgae-derived single cell oils

Abstract

Abstract Marine macroalgae (seaweed) has many advantages over terrestrial crops as a source of renewable biomass but is severely underutilised at present, especially within Europe. In particular, macroalgae has elevated poly- and monosaccharide content, making it an ideal feedstock as a heterotrophic fermentation sugar source for the production of higher value chemicals. Recent reports have detailed the suitability of seaweeds as a feedstock for the production of single-cell oils (SCOs) which have application in food, oleochemicals and fuels. It is proposed that a biorefinery system based on the production of SCOs alongside other secondary metabolites, has the potential to provide a sustainable replacement to terrestrial oils such as palm oil. This work therefore evaluates, for the first time, the environmental and economic sustainability of a production process for SCOs from seaweed Saccharina latissima using the oleaginous yeast Metschnikowia pulcherrima. Two alternative fermentation systems were considered, and uncertainties associated with the seasonal variation in seaweed carbohydrate yield and fermentation performance were integrated into the analysis. From an environmental perspective, the work indicates that seaweed derived SCO lipids and fats can be comparable to a terrestrial oil mix, with a potential climate change impact ranging between 2.5 and 9.9\u202fkg CO2 eq. kg−1 refined SCO. Interestingly and of particular significance, environmental impacts are mainly dominated by energy demand within fermentation and upstream processing steps. From an economic perspective, a break-even selling price for the oil was determined as between €5,300-€31,000 tonne−1 refined SCO, which was highly dependent on cost of the seaweed feedstock. Overall, we demonstrate that key uncertainties relating to seaweed cultivation costs and hydrolysate fermentation at scale result in a large range in values for environmental impact and economic return on investment. Yet even within the constraints and limitations of current knowhow, seaweed already offers a viable proposition for the competitive production of exotic oils similar to cocoa or shea butter in price and nature.