Co-production of biodiesel and alginate from Laminaria japonica

A process to produce both biodiesel and alginate in an integrated manner from a brown seaweed, Laminaria japonica, was established. Mannitol, a major carbon constituent in L. japonica, served to produce neutral lipids via the heterotrophic cultivation of an oleaginous yeast, Cryptococcus sp.; and simultaneously alginate, a high value product, was extracted to enhance the economic feasibility of the entire process. Only autoclave pretreatment, without need of any chemical agents, was enough to recover all the essential nutrients for the yeast cultivation. Specifically, it could recover 6.4 g L^-1 of mannitol to a degree comparable to 6.6 g L^-1 obtained by acid-aided pretreatment using 1.5% (v/v) of H₂SO₄. Maximum fatty acids methyl esters (FAME) content was 30.37% with FAME productivity of 0.56 g L^-1 d^-1, and the produced FAME could meet the biodiesel quality standards. Na₂CO₃-based method showed the best efficiency of alginate recovery, yielding 21.06% (w/w). This study supports that L. japonica can indeed be a promising low-cost feedstock for biodiesel production, and it is more so when a high-value product alginate is co-produced.