Greenhouse Gas Sequestration by Algae – Energy and Greenhouse Gas Life Cycle Studies

We have examined various scenarios involving the growth of algae and the sequestering of carbon during its growth. End-uses for algae are found in the production of food supplements for humans; animal feed; oil extraction and its transesterification to produce biodiesel; electricity production upon combustion directly or by transforming the algae to methane anaerobically; or fuel production via pyrolysis, gasification or anaerobic digestion. In every case, the greenhouse gases sequestered by the algae are released into the atmosphere, so that greenhouse gas benefits arise only as offsets when the algal use displaces the combustion of a fossil fuel in a vehicle or for the production of electricity. This paper examines the greenhouse gas, costs and energy balance on a life-cycle basis for algae grown in salt-water ponds and used to produce biodiesel and electricity. Under the conditions described and the data assumed, it is shown that it is possible to produce algal biodiesel at less cost and with a substantial greenhouse gas and energy balance advantage over fossil diesel. However, when scaled up to large commercial production levels, the costs may exceed those for fossil diesel. The economic viability is highly dependent upon algae with high oil yields capable of high production year-round, which has yet to be demonstrated on a commercial scale.