Rice straw is pretreated with KOH aqueous solution and the resulting liquid is used to synthesize a black liquor-derived porous carbon (BLPC) in which KOH acts as both lignin extraction solvent and chemical activation agent. The addition of melamine into the black liquor leads to an increase in the surface area (2646 m(2) g(-1)), pore volume (1.285 cm(3) g(-1)) and promotes the formation of nitrogen covalent bonds in the carbon materials (N-BLPC). Melamine used as additive has dual roles as nitrogen source and pore modifier of the carbon material. The as-prepared materials have specific capacitances of 242 F g(-1), (BLPC) and 337 F (N-BLPC) when used as electrodes in 6 M KOH electrolyte at a current density of 0.5 A g(-1). The assembled N-BLPC-based symmetric supercapacitor shows stable cycling (>98% retention after 3000 cycles at 10 A g(-1)). The proposed strategy offers a facile method to produce porous carbons from waste black liquor in biorefinery or pulp and paper processes. (C) 2017 Elsevier B.V. All rights reserved.