Hydrothermal Liquefaction of Bacteria and Yeast Monocultures

We hydrothermally treated monocultures of Escherichia coli, Pseudomonas putida, Bacillus subtilis, and Saccharomyces cerevisiae at isothermal (350 °C for 60 min) and fast (rapid heating for 1 min) liquefaction conditions. Fast hydrothermal liquefaction (HTL) of P. putida and S. cerevisiae produced the highest biocrude yields of 47 ± 13 and 48 ± 9 wt %, respectively. Biocrudes generated via fast HTL were always richer in O and N and had a higher yield of hexane-insoluble products. Isothermal HTL of all microorganisms always produced an aqueous phase richer in NH3 than the aqueous phase from fast HTL. Up to 62 ± 9% of the chemical energy in the biomass could be recovered in the biocrude product fraction. These results demonstrate the feasibility of applying HTL to produce high yields of biocrude from bacteria and yeast that are high in protein [>80 wt %, dry and ash-free basis (daf)] and low in lipids (<3 wt %, daf). Such microorganisms could serve as a renewable feedstock for biofuels.