Biocrude production and heavy metal migration during hydrothermal liquefaction of swine manure

The production of swine manure has increased constantly with the continuing development of the livestock industry. Swine manure contains a large amount of nutrients, heavy metals, and pathogens, which may cause severe environmental pollution when released into the environment without proper treatment. Hydrothermal liquefaction (HTL) has been recognized as a promising technology to degrade wet biowaste and recovery energy in the form of biocrude oil. This study investigated the effects of the operational parameters, including the temperature (220–370 °C), the retention time (0–90 min) and the total solid content (TS) (10–30%) on the HTL of swine manure. The volatile solid (VS) removal rate of swine manure reached up to around 90%, whereas the highest biocrude oil yield was 25.58% (based on dry biomass). FT-IR analysis indicated that the biocrude oil mainly consisted of esters, acids, aldehydes and hydrocarbon compounds. The results of elemental distribution showed that over 70% of the heavy metal elements (Zn, Cu, As, Pb and Cd) were accumulated in the solid residue. This study provides a basic depiction of energy recovery and the mitigation of environmental concerns when utilizing swine manure as a feedstock for HTL.