Carbon sequestration and the role of biological carbon mitigation: A review

Climate change and rising atmospheric CO2 levels have become much debated environmental issues in recent years. Point source emissions of CO2 from industrialised processes such as power generation and cement production account for much of this increase. Direct carbon sequestration and storage techniques such as geological injection have large storage capacities, however these methods are very cost inefficient and have not been proved safe for long term sequestration. A novel approach to offsetting emissions is through direct biological carbon mitigation where CO2 from the flue gases of point sources is used to cultivate photosynthetic autotrophic organisms. The produced biomass can subsequently be converted into biofuels, bio-chemicals, food or animal feed. These useful by-products provide revenue to finance the carbon mitigation process. Large-scale cultivation of biological media on site at a power generation plant means that substantial amounts of biomass could be readily available for co-firing in the plant, thus decreasing the demand for fossil fuels. This review gives an overview of the most suitable strains of microalgae for the purpose of carbon mitigation while the challenges associated with carbon mitigation strategies such as capital costs, environmental issues, and cultivation of microalgae using flue gases will also be assessed. Selected media will be required to have a high CO2 fixing rate, a rapid growth rate, while being easily cultivated on a large scale in order to generate a large biomass yield and produce valuable by-products to offset the costs of carbon mitigation. An economic balance is also discussed to give an indication of the cost benefits in the implementation of biological carbon mitigation policies as a solution to the high capital and running costs of large scale microalgal production.