(670a) Hydrothermal Liquefaction of E. Coli, P. Putida, S. Cerevisiae, and B. Subtilis: Effect of Biomass Selection, Growth Media, and Reaction Conditions

Bacteria and yeasts are widely used in industrial processes as biocatalysts that turn feedstock substrates into finished products (specialty chemicals, food products, biofuels, etc.). The associated microbial biomass produced is often only considered a low-value co-product or discarded as a waste, yet this biomass often accounts for a large amount of the chemical energy in the process. Hydrothermal liquefaction, a high-temperature and high-pressure process, can convert wet biomass slurries into energy-dense bio-oils. The pairing of large-scale cultivation of microorganisms and wet hydrothermal processing of biomass creates an opportunity to produce a renewable biofuel from low-value materials.

We cultivated Escherichia coli, Pseudomonas putida, Bacillus subtilis, and Saccharomyces cerevisiae and subjected the biomass slurries to hydrothermal treatment at fast and conventional liquefaction conditions. E. coli and S. cerevisiae are bacterial and yeast strains frequently used in industrial bioprocesses. P. putida has a diverse metabolic network, which makes it a candidate for growth on complex waste streams. B. subtilis, a widely studied Gram-positive bacterium, was included to investigate the impact of its differing cellular composition (particularly in the cell wall) on liquefaction products when compared to the other two Gram-negative bacteria. We examined the effect of bacteria selection, growth media, cellular structure, and hydrothermal treatment conditions. We found that bio-oils treated at fast liquefaction conditions had higher yields but were richer in hexane insoluble products. The total yield of bio-oil was similar between cultures grown with rich and minimal media. We also determined the molecular and elemental composition of the liquefaction products.