Co-hydrothermal liquefaction of wastewater-grown algae and crude glycerol: A novel strategy of bio-crude oil-aqueous separation and techno-economic analysis for bio-crude oil recovery and upgrading

Crude glycerol was introduced into hydrothermal liquefaction of wastewater-grown algae, Galdieria sulphuraria, to improve yield and energy recovery of bio-crude oil, and to enable solvent-free oil/aqueous phase separation by gravity. Co-hydrothermal liquefaction of 5, 12.5, and 20 wt% solids loading algae and crude glycerol at 350 °C for 30 min gave bio-crude oil yields of 58.8 ± 0.8, 65.5 ± 1.5 and 56.2 ± 1.5 wt%, compared to 14.6 ± 0.1 wt% and 58.1 ± 0.8 wt% for algae alone and crude glycerol alone, respectively. Solvent-free bio-crude oil was upgraded into a liquid biofuel at a yield of 48.1 ± 0.8 wt% and higher heating value of 43.7 ± 0.1 MJ/kg. Incorporation of the co-hydrothermal liquefaction experimental yields and solvent-free phase separation into a techno-economic model for biofuels from hydrothermal liquefaction of algae resulted in a calculated minimum fuel sell price of $0.38–1.24 per liter gasoline equivalent, suggesting substantial potential for co-hydrothermal liquefaction of low-lipid algae with crude glycerol as a competitive strategy for economic 3rd generation biofuel production.