Integrated biodiesel and biopolymer production from <i>Nannochloropsis</i> biomass: a closed-loop biorefinery approach

This study investigates the potential of utilizing deoiled algal biomass (DAB) derived from <i>Nannochloropsis</i> sp. after biodiesel production for biopolymer synthesis in a closed-loop system. The investigation demonstrates the feasibility of employing a biorefinery-based approach to produce both biodiesel and biopolymer, specifically polyhydroxybutyrate (PHB), from algae residues. Algal oil was extracted using the Bligh and Dyer method, with an optimal lipid yield achieved at 45 °C after 30 minutes, resulting in a lipid content of 29.41 wt%. Biodiesel conversion of the extracted oil was achieved with a 90.4 wt% efficiency using NaOH as a catalyst. The residual deoiled cake was further utilized for PHB production, achieving a maximum yield of 0.39 g PHB per g DOC (39% of DOC dry weight). The results highlight the potential of integrating biodiesel and biopolymer production into a single biorefinery process, promoting resource efficiency and sustainability. This approach highlights the viability of a circular bioeconomy for microalgal biorefinery systems, with minimum waste generation and maximum resource utilization.