Macroalgae for biofuels
Globally, in order to meet our future needs for transport fuels, there is a huge requirement for new sources of liquid (or liquefiable) energy. Population growth and associated needs for increased food production drives a scenario of land space and water resource scarcity, which limits the potential contribution that terrestrial biofuel crops can make to future energy needs in a CO2-rich world. In addition, intensive production of terrestrial bio-energy crops requires large amounts of energy-intensive chemical fertiliser that contributes to diffuse pollution and is currently dependent on non-renewable sources of phosphorus. Furthermore, NIMBY and ECO attitudes may preclude extensive use of land for bio-energy production.
Marine macroalgal production has, in principle, huge potential to provide a biomass substrate that can be used for energy production (alcohol from fermentation, methane from Anaerobic Digestion). Harvest of wild macroalgae is currently practiced in the Americas, SE Asia and Europe but, as macroalgal forests are regarded as biodiversity hot spots providing important ecosystem services, and because of the scale required for economic biofuel production, wild harvest is unlikely to be the major source.
The technology to culture macroalgae without the need for additional fertiliser and with low dependence on freshwater is well developed in Europe, and lessons can be learned from the experience of industrial scale culture as practiced in the Far East: World aquatic plant production in 2006 reached 15.1Mt of which 10.9Mt originated from China (FAO 2008). Yields of up to 60t dw.ha-1y-1 have been reported for cultured Laminaria japonica in China.
The potential of macroalgae as a source of power is explicitly acknowledged in the UK Renewable Energy Strategy. The large brown macroalgae - or kelp - are perhaps the greatest potential source of marine biofuel. Kelp are large seaweeds, part of the brown algae class that are known for their high growth rates. To grow kelp requires nutrient-rich water below 20 °C. The concept of marine macroalgal biomass for biofuel is not new: in the late 1960s Chynoweth at IGT Chicago researched farming giant kelp (Macrocystis pyrifera) as a substrate demonstrating high conversion efficiencies, rapid conversion rates and good process stability. However, their attempts to farm the seaweeds failed through a lack of knowledge of seaweed biology and offshore farming methods.
Currently worldwide production of seaweed is placed at 6.9 million tonnes per annum, equivalent to US$6 billion. Of this just 4.3% is produced in Europe, while 90% is produced within the Far East. Kelp farming is currently undertaken in Scotland, Northern Ireland and Ireland (where production is 8,000 tonnes per annum).
Global interest in seaweed culture is growing rapidly with significant projects underway in Chile and Australia.