Biological CO2 sequestration using algal reactors is one of the most promising and environmentally benign technologies to sequester CO2. This research study was taken up to alleviate certain limitations associated with the technology such as low CO2 sequestration efficiency and low biomass yields. The study demonstrates an increase in CO2 sequestration efficiency by maneuvering chemically aided biological sequestration of CO2. Chlorella sp. and Spirulina platensis showed 46% and 39% mean fixation efficiency, respectively, at input CO2 concentration of 10%. The effect of acetazolamide, a potent carbonic anhydrase inhibitor, on CO2 sequestration efficiency was studied to demonstrate the role of carbonic anhydrase in calcite deposition. Calcite formed by both species was characterized by scanning electron microscopy coupled electron dispersive spectroscopy and X-ray diffraction. The overall scheme of calcite deposition coupled CO2 fixation with commercially utilizable biomass as a product seems a viable option in the efforts to sequester increasing CO2 emissions. (C) 2009 Elsevier Ltd. All rights reserved.