Hydrothermal liquefaction of typical livestock manures in China: Biocrude oil production and migration of heavy metals

Abstract

Hydrothermal liquefaction (HTL) of six typical animal manures in China (Swine manure, Dairy manure, Beef manure, Laying hen manure, Broiler manure, and Sheep manure) was performed in this study. The highest biocrude oil yield was 30.85% (dry ash-free basis, daf) and was obtained from swine manure at 340 °C, whereas the biocrude yields from other manures ranged from 15.03% (daf) to 25.47% (daf). The study demonstrated that besides biocrude oil production, the majority of heavy metals, i.e. 70%–98% of Zn and Cu, 71%–99% of Pb, 87%–98% of Cd and 20%–75% of As, in all six types of typical animal manures were concentrated into the solid residue after HTL. The mobile heavy metal fractions in the manure were transformed into more structurally stable forms in the solid residue. Environmental risks of heavy metals in the feedstock and solid residue were further assessed based on individual contamination factors and global contamination factor codes. Interestingly, ecological risk levels of most heavy metals in all manures were dramatically decreased from high-medium to low-moderate risk via HTL. It is feasible to simultaneously produce biocrude oil and control the migration of heavy metals in livestock manure via HTL.