Biochar, a stable, carbon-rich solid produced during biomass pyrolysis, has been widely used in soil conditioning. A promising option to alleviate the problem of sludge management. In this study, Cr, Ni, Zn, Cd, As, Pb and Cu were studied owing to their relatively high content in the sludge and their potential to cause environmental damage. Sludge-biochars were produced at different temperatures