Algae

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Since biomass cultivation on land poses competition to food security, perhaps we can consider using other forms of biomass from the sea? Can algae be a promising source of biomass energy, since they generally do not compete with food crops for resources and land?

It appears that there has already been strong interest in algae biofuel development. A recent Time article mentioned that while technology to make cellulosic ethanol or biofuel from algae is available, there are high costs and challenges associated with scaling the production up sufficiently to compete with oil.

Liu et al (2013)'s life cycle analysis (LCA) on  algae-to-energy systems with hydrothermal liquefaction (HTL) showed that substantively lower GHG emissions can be achieved compared to gasoline as depicted by the chart below for various scenarios. Nonetheless, conventional fossil fuels such as gasoline maintain the upper edge as they enjoy a higher Energy Return on Investment (EROI).

Source: Liu et al (2013) 

HTL is of particular commercial interest because it is able to seamlessly integrates with existing petroleum refining infrastructure. During hydrothermal liquefaction, high moisture biomass is subjected to elevated temperatures and pressures, similar to the natural geological processes that has produced existing stocks of fossil fuel.

Apart from cost considerations, one should also consider the CO2 mitigation potential of algae biofuels through a life cycle analysis. Andres et al (2010) compared the environmental impact from algae production with various biofuel crops such as switchgrass, canola, and corn farming. The results indicate that conventional crops have lower environmental impacts than algae in energy use and GHG emissions. It appears that the large environmental footprint of algae cultivation is driven predominantly by upstream impacts, such as the demand for CO2 and fertilizer. To reduce these impacts, wastewater could be used to offset most of the environmental burdens associated with algae.

Looks like it will still be some way to go before algae biomass can become a marketable and truly climate-friendly alternative energy technology.