The migration and transformation behavior of heavy metals during co-liquefaction of municipal sewage sludge and lignocellulosic biomass.

Co-liquefaction of municipal sewage sludge (MSS) and heavy metal (HM) contaminated lignocellulosic biomass (rice straw or wood sawdust) was conducted at 300 °C with ethanol as the solvent to study the transformation behavior of HMs (e.g., Cu, Cd, Pb, Cr, Zn, and Ni). The results indicate that HMs in rice straw or wood sawdust transferred heavily to bio-oils (up to 10-25% of the total Cu, Cd, and Zn) when they were liquefied individually, compared with MSS with only ∼5% distributed to bio-oil. The bio-available fraction of HMs in bio-chars and bio-oils produced from liquefaction of individual biomass were assessed to show medium to high risk to the environment. Co-liquefaction promoted the distribution of HMs to solid bio-char. Moreover, co-liquefaction benefited the immobilization of HMs in bio-chars and bio-oils. Synergistic effects were found for HMs immobilization during co-liquefaction.