The study was conducted to explore the potential of spent biomass of a hydrogen producing cyanobacterium, Nostoc linckia for removal of Co(II) from aqueous solution. The biomass waste generated from a lab-scale hydrogen bioreactor was immobilized in calcium alginate and used as a biosorbent. Kinetic studies indicated that biosorption of Co(II) on the cyanobacterial biomass followed pseudo second order model with an equilibrium time of 125 min. Response surface methodology (RSM) was used to design experiments for optimization of pH (1.0-6.0), temperature (25-45 degrees C) and initial metal concentration (10-100 mg/L) for achieving maximum removal of Co(II) by the biosorbent. The data was fitted to a second-order polynomial equation and highly significant regression coefficients confirmed that the model could be applied for obtaining the desired response within the design range using the present biosorbent. The response surface data showed a maximum of 97% metal removal at pH 3.5 and 25 degrees C temperature at initial metal concentrations of 10 mg/L (C) 2011 Elsevier B.V. All rights reserved.