초록
<P><B>Abstract</B></P> <P>Production of microalgal biomass for feed and fuels demands unsustainable large amounts of fertilizers. The most broadly considered alternative sources of nutrients/fertilizer for microalgae are wastewater and internal recycling in closed-loop production platforms. However, these strategies largely disable co-production of feed and fuel in biomass biorefineries for an increased economic and environmental feasibility.</P> <P>In this study, we aimed at providing proof-of-concept for a semi-closed loop microalgal production-platform and biomass biorefinery for ethanol and feed from renewable resources of N and P. Atmospheric N<SUB>2</SUB> was assimilated into a N<SUB>2</SUB>-fixing cyanobacterial biomass, which sustained growth of a microalga that accumulated high levels of carbohydrates (up to 60% (w/w)) as a sole source of fertilizer. The microalgal biomass was efficiently saccharified with H<SUB>2</SUB>SO<SUB>4</SUB>, which was recycled to release soluble PO<SUB>4</SUB> <SUP>3-</SUP> from bone meal as a renewable source of P. Fermenting these P-enriched preparations with yeasts quantitatively produced ethanol at theoretical yields, a concentration of up to 50 g ethanol. L<SUP>−1</SUP> and a yield of 0.25 g ethanol. g biomass<SUP>−1</SUP>. Calculations suggested a potential yield from 7600 to 10,800 L ethanol. ha<SUP>−1</SUP>. year<SUP>−1</SUP>, under Buenos Aires environmental conditions, which would be higher than that currently obtained from maize feedstocks. The residual fermentation vinasse, supplemented with P and containing other downstream-process reagents, was recycled as a sole source of macronutrients for the cultivation of the N<SUB>2</SUB>-fixing cyanobacterium to close the production cycle. Water recycling and co-production of residual biomass enriched in fat and protein as potential feed are also shown. This semi-closed loop biomass production-platform reconciles the concepts of microalgal biomass biorefineries for the co-production of feedstocks for biofuels and feed and nutrients recycling in closed-loop systems that largely minimizes production of waste.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A multitrophic semi-closed loop biomass production platform is proposed. </LI> <LI> N and P fertilizers were produced on site from air and bone meal, respectively. </LI> <LI> Ethanol was produced at 0.25 g. g microlgal biomass<SUP>−1</SUP> along with animal feed. </LI> <LI> Sulfuric acid integrated biomass saccharification and efficient P recovery. </LI> <LI> Nutrients in vinasse and water were recycled to close the production cycle. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>