Study on the bio-oil characterization and heavy metals distribution during the aqueous phase recycling in the hydrothermal liquefaction of As-enriched Pteris vittata L.

The hydrothermal liquefaction (HTL) of As enriched Pteris vittata L. (PVL, hyper-accumulator biomass) was performed with the recycled aqueous phase as reaction medium, aiming to dispose the biomass with high water content and produce high-quality bio-oil. After three times of aqueous phase recycling at 275 °C, 30 min, the bio-oil yield increased to 30.32% from 21.54% and the higher heating value (HHV, 28.51 MJ/kg) of the bio-oil was higher than that of the bio-oil from HTL with pure water (26.80 MJ/kg). The main compounds detected in bio-oils were phenols, ketones, hydrocarbons, and aldehydes. Acetic acid (17.21-24.77 mg/mL) was dominant in the aqueous phases, resulting in the low pH (4.31-4.89). The heavy metals (Cu, Pb, Zn, Cd) mainly remained in bio-char whereas As was transferred to aqueous phase. Thus, HTL by aqueous phase recycling could be a promising way for PVL treatment to obtain high-quality bio-oil and arsenic recovery.