Third generation biofuels: from algae to oil
Getting oil from micro-algae is one of the most promising way to produce biodiesel in the future. There are several advantages of growing algae to produce oil. One is that the yield is one order of magnitude larger than for oilseeds cultivated inland. Another advantage is that there is no competition with food crops. Furthermore algae can be continuously harvested and could be used coupled to an industrial facility emitting CO2: instead of emitting CO2 oil can be produced.
There are between 200 000 and a million of different species of algae. Some of them can grow in extreme conditions. Micro-algae are interesting because they can produce oil with a higher yield compared to oilseeds cultivated inland. For example, the yield of micro-algae is between » 36 t/year/ha and 180 t/year/ha of dry matter. The lower bound (36 t/year/ha) has to be compared with rape (» 3.3 t/year/ha) or sunflower (» 2.2 t/year/ha). Indeed more than 20 t of oil can be produced with typical micro-algae compared to 6-8 t of oil for palm oil which is one of the most efficient inland crops for that.
There are many micro-algae able to produce more than half of their weight of oil. This is for example the case of Chlorella prothecoides, Dunalliela tertiolecta, Nannochloropsis, etc. In Europe France, Germany, Great-Britain, Malta, Netherlands and Spain are working on this subject.
There are nevertheless still many problems to solve before reaching an industrial stage and research is urgently needed. Studies about the impact of cultivating micro-algae in great quantities are required. It is also necessary to find the optimal conditions for growing and selecting the right species. For example, the yield dramatically decreases with the outside temperature. Stability and resistance against microbes of viruses are important issues if large areas are cultivated. Infection by other algae species might also be a problem. Genetic engineering will play a key role in this research.
Developing algae oil at an industrial scale is an important issue since transportation is mostly based on petroleum products. Mastering micro-algea crops to produce oil is important for energy safety. The DOE has estimated that an area in the sea of the size of the state of Maryland could provide enough biofuel to replace oil used in the USA.
Figure : indicative oil yields for various oil seeds and algae. Data from www.oilgae.com