Carbon residue is a by-product from the biomass gasification process in which heat and power are generated. In this study, carbon residue was chemically activated and the effect of this activation process on the adsorption properties was investigated. A chemically activated carbon residue was used as an adsorbent for the removal of phosphate and nitrate in an aqueous solution. The general idea is that the carbon residue could first be used as a low cost adsorbent for phosphate and nitrate ions removal, e.g. from wastewaters, and after that it could be used as a nitrogen and phosphorus rich forest fertiliser. Based on the results, the most effective pH value for phosphate removal was 6, 4 and 6 for activated carbon residue, carbon residue and activated carbon respectively. Optimum pH value for nitrate removal was 6 for activated carbon residue and carbon residue, and 4 for activated carbon. The optimum concentrations for the initial phosphate solutions for activated carbon residue, carbon residue and activated carbon were 25,50 and 25 mg L-1 respectively. For nitrate, the optimal concentration was 25 mg L-1 for all adsorbents. Phosphate and nitrate adsorption kinetics were well fitted by the pseudo-second-order kinetic model for all studied adsorbents. Phosphate and nitrate adsorption onto activated carbon residue obey well Langmuir adsorption isotherm. (c) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.