Wastewater treatment high rate algal pond biomass for bio-crude oil production

•Temperature effect on bio-crude production from wastewater algae was investigated.•The bio-crude yield increased with temperature.•The bio-crude higher heating values ranged 37.5–38.9kJ/g.•Up to 47.4% of the biomass energy (19.7kJ/g) was recovered in the bio-crudes. This study investigates the production potential of bio-crude from wastewater treatment high rate algal pond (WWT HRAP) biomass in terms of yield, elemental/chemical composition and higher heating value (HHV). Hydrothermal liquefaction (HTL) of the biomass slurry (2.2wt% solid content, 19.7kJ/g HHV) was conducted at a range of temperatures (150–300°C) for one hour. The bio-crude yield and HHV varied in range of 3.1–24.9wt% and 37.5–38.9kJ/g, respectively. The bio-crudes were comprised of 71–72.4wt% carbon, 0.9–4.8wt% nitrogen, 8.7–9.8wt% hydrogen and 12–15.7wt% oxygen. GC–MS analysis indicated that pyrroles, indoles, amides and fatty acids were the most abundant bio-crude compounds. HTL of WWT HRAP biomass resulted, also, in production of 10.5–26wt% water-soluble compounds (containing up to 293mg/L ammonia), 1.0–9.3wt% gas and 44.8–85.5wt% solid residue (12.2–18.1kJ/g). The aqueous phase has a great potential to be used as an ammonia source for further algal cultivation and the solid residue could be used as a process fuel source.