Review on hydrothermal liquefaction aqueous phase as a valuable resource for biofuels, bio-hydrogen and valuable bio-chemicals recovery

Hydrothermal liquefaction (HTL) of biomass results in the formation of bio-oil, aqueous phase (HTL-AP), bio-char, and gaseous products. Safer disposal of HTL-AP is difficult on an industrial scale since it comprises low molecular acid compounds. This review provides a comprehensive note on the recent articles published on the effective usage of HTL-AP for the recovery of valuable compounds. Thermo-chemical and biological processes are the preferred techniques for the recovery of biofuel, platform chemicals from HTL-AP. From this review, it was evident that the composition of HTL-AP and product recovery are the integrated pathways, which depend on each other. Substitute as reaction medium in HTL process, growth medium for algae and microbes are the most common mode of reuse and recycle of HTL-AP. Future research is needed to depict the mechanism of HTL process when HTL-AP is used as a reaction medium on an industrial scale. Need to find a solution for the hindrance in commercializing HTL process and recovery of value-added compounds from HTL-AP from lab scale to industry level. Integrated pathways on reuse and HTL-AP recycle helps in reduced environmental concerns and sustainable production of bio-products.

Valorizing a hydrothermal liquefaction aqueous phase through co-production of chemicals and lipids using the oleaginous yeast Yarrowia lipolytica

Hydrothermal liquefaction is a promising technology to upgrade wet organic waste into a biocrude oil for diesel or jet fuel; however, this process generates an acid-rich aqueous phase which poses disposal issues. This hydrothermal liquefaction aqueous phase (HTL-AP) contains organic acids, phenol, and other toxins. This work demonstrates that Y. lipolytica as a unique host to valorize HTL-AP into a variety of co-products. Specifically, strains of Y. lipolytica can tolerate HTL-AP at 10% in defined media and 25% in rich media. The addition of HTL-AP enhances production of the polymer precursor itaconic acid by 3-fold and the polyketide triacetic acid lactone at least 2-fold. Additional co-products (lipids and citric acid) were produced in these fermentations. Finally, bioreactor cultivation enabled 21.6 g/L triacetic acid lactone from 20% HTL-AP in mixed sugar hydrolysate. These results demonstrate the first use of Y. lipolytica in HTL-AP valorization toward production of a portfolio of value-added compounds.