Influence of sewage sludge-based activated carbon and temperature on the liquefaction of sewage sludge: Yield and composition of bio-oil, immobilization and risk assessment of heavy metals

The influence of sewage sludge-based activated carbons (SSAC) on sewage sludge liquefaction has been carried out at 350 and 400 °C. SSAC increased the yield and energy density of bio-oil at 350 °C. The metallic compounds were the catalytic factor of SSAC obtained at 550 °C (SSAC-550), while carbon was the catalytic factor of SSAC obtained at 650 °C. Liquefaction with SSAC redistributed the species of heavy metals in solid residue (SR). With the addition of SSAC, the risk of Cu, Zn and Pb decreased at 350 °C, while at 400 °C the risk of Cd, Cu, and Zn were decreased. Ecological risk index indicated that 400 °C was preferable for the toxicity decrement of SR, while risk assessment code indicated that SR obtained at 350 °C contained lower risk. Considering the bio-oil yield, liquefaction at 350 °C with SSAC-550 was preferable.