Recycling nutrients from a sequential hydrothermal liquefaction process for microalgae culture

Nutrient supply and reuse are critical considerations for culturing and processing algae as feedstock for biofuel production. Sequential Hydrothermal Liquefaction (SEQHTL) is used to convert microalgae biomass to biofuel and co-products. Along with biocrude and biochar of the co-products, SEQHTL produces aqueous products with high concentrations of phosphate, organic nitrogen and polysaccharides. In this study, three representative microalgaes, Chlorella sorokiniana, Chlorella vulgaris and Galdieria sulphuraria 5587.1 were evaluated for utilizing the nutrients recovered from the aqueous products of SEQTHL. C. sorokiniana and C. vulgaris exhibited the ability to hydrolyze polysaccharides, using 77% and 64% of the polysaccharides and removing 94% to 95% of the phosphate, respectively. G. sulphuraria on the other hand, could not use the polysaccharides. All three species could completely assimilate ammonia and use 33%-43% of the organic nitrogen. There were no significant differences in terms of lipid contents and composition, C. sorokiniana and C. vulgaris had higher lipid content (18% of DCW) than what G. sulphuraria did (only 10% of DCW). The findings indicate that although being species dependent, it is possible to reuse the nutrients recovered from SEQHTL of algal biomass for algal culture.