Abstract
[Display omitted]
•Demetalization of SS by a modified BCR sequential extraction before liquefaction.•Demetalization had little effect on oil quantity, but had positive effect on quality.•Bio-oil and bio-char produced after demetalization pose low environmental risk.•Removal of F1 and F2 fractions of heavy metals before liquefaction is recommended.•The expansion of BCR can be widely used to study the heavy metal in other processes.
Demetalization of sewage sludge (SS) by sequential extraction before liquefaction was implemented to produce cleaner bio-char and bio-oil. Demetalization steps 1 and 2 did not cause much organic matter loss on SS, and thus the bio-oil and bio-char yields and the compositions of bio-oils were also not affected significantly. However, the demetalization procedures resulted in the production of cleaner bio-chars and bio-oils. The total concentrations and the acid soluble/exchangeable fraction (F1 fraction, the most toxic heavy metal fraction) of heavy metals (Cu, Cr, Pb, Zn, and Cd) in these products were significantly reduced and the environmental risks of these products were also relived considerably compared with those produced from raw SS, respectively. Additionally, these bio-oils had less heavy fractions. Demetalization processes with removal of F1 and F2 fractions of heavy metals would benefit the production of cleaner bio-char and bio-oil by liquefaction of heavy metal abundant biomass like SS.