Aim of the study was to investigate how hydrothermal carbonization changes adsorption efficiency toward metal ions of typical sludges. Hydrothermal carbonization is a novel and green method of treating biomasses. Reactions take place in an aqueous environment at relatively mild temperature and high pressure resulting a different end biomass structure than obtained from traditional pyrolysis. Anaerobically digested sludge (ADS) and pulp and paper industry sludge (INS) were utilized as a feedstock. Adsorption behavior of ADS and INS was examined towards Pb(II), Cr(III), Cr(VI), As(III) and As(V). Both ADS and INS were found to remove Pb(II) effectively and followed Sips adsorption isotherm. Adsorption kinetics was fast and followed pseudo-second order model. Furthermore, intraparticle diffusion was observed to be partly responsible in the adsorption process. Hydrothermal carbonization indicated high potential for the production of novel carbonaceous materials for metal removal from waters. (C) 2013 Elsevier Ltd. All rights reserved.