Hydrothermal liquefaction of mixed-culture algal biomass from wastewater treatment system into bio-crude oil

In this study, a mixed-culture algal biomass harvested from a functioning wastewater treatment system (AW) was hydrothermally converted into bio-crude oils. The highest bio-crude oil yield (49% of volatile matter) and the highest energy recovery were obtained at 300 °C with 1 h retention time. The highest heating value of the bio-crude oil was 33.3 MJ/kg, produced at 320 °C and 1 h retention time. Thermogravimetric analysis showed approximately 60% of the bio-crude oils were distilled in the range of 200–550 °C; and the solid residue might be suitable for use in asphalt. GC–MS results indicated that the bio-crude oil contained hydrocarbons and fatty acids, while the aqueous product was rich in organic acids and cyclic amines. The nitrogen recovery (NR) in the bio-crude oil ranged from 8.41% to 16.8%, which was lower than the typical range of 25%–53% from previous studies.