Next Generation Energy is managed and written entirely by Seed editors and expert guest bloggers. Read more about them Go to most gas stations and there are two separate choices, gasoline and diesel. While your car or truck will run on one or the other, they are both refined from the same substance, crude oil. Biodiesel and bioethanol, however, are derived from very different sources. Ethanol is a product of fermenting simple sugars derived from plants; biodiesel is the product of esterified plant lipids (fats, oils, and waxes). Terrestrial plants have limited potential to yield significant amounts of oils though there are perhaps some opportunities worth discussing later such as Jatropha.
Cyanobacteria, also known as blue-green algae is a single cell
photosynthetic organisms that contains both chlorophyll (green)
and phycocyanin (blue) pigments. The species pictured, Spirulina
is cultivated around the world, and is used as a human dietary
supplement.
The oil yields are simply not high enough. However, biodiesel as a fuel lacks some of the drawbacks of ethanol, which has one third less energy than gasoline per unit volume and is hydroscopic hygroscopic. The lower heat of combustion rate results in less power and lower miles per gallon. Biodiesel on the other hand is roughly equivalent to diesel and as many of you know, Rudolph Diesel designed his first engines to run on peanut oil.
Various photosynthetic microbes are comprised of up 50% of their body (a single cell) weight in lipids. Why not cultivate photosynthetic microbes for their oils? Two of the most attractive aspects of this endeavor are land and water use. Sources of water too saline for irrigation or human consumption can be used in bioreactors that are suitable for virtually any land. The rate of production is considerably more rapid than any field crop as well. Without a long life cycle and seasonal growth, a much more continuous flow of biodiesel is possible as opposed to intermittent harvest of trees and grasses. This is a tried and practical approach. Today Spirulina is cultivation in small bioreactors and large "raceways" around the world.
The rapid life cycle also aids in research, more lifecycles to do experiments in less time and quick to develop a genetically modified strain. This brings us to some of the shortcomings. As with GM livestock and crops, a risk assessment will need to be conducted on this somewhat new example of a well-tested paradigm, GM cyanobacteria. Contamination can also be a serious issue. Not regarding escape, but unwanted organisms living in the bioreactors as noxious interlopers. Thus far, Spirulina raceways are relatively immune or at least tolerant to contamination, but other microbes might not prove to be so.
Aerial photos of the 90-acre microalgae production facility, Kona, Hawaii.
Note: green ponds culturing Spirulina and red ponds with Haematococcus
pluvialis.
The critical aspect of harvesting the cells and oil is not straightforward. Experimentally and in pilot plants, this is done by centrifugation. The centrifuges and the pumps used to fill tanks and move cultures from one tank to another require a prohibitive amount of energy when the cyanobacteria yield only 2.5g diesel/L of culture (back of the optimistic envelope calculation). One cost saving approach is to simply use gravity.
These seem to me to be solvable problems. One necessary step is to increase the number of scientists that study cyanobacteria. Today there are only a handful dedicated to their biochemistry and genetics. However, there are numerous start-up companies focusing on developing biodiesel platforms and interestingly the Department of Defense would like to use mobile bioreactors to fuel military forces in the field. There is in fact a rich history of biodiesel research and development that was largely killed in the 1990s by cheap oil. See this 3.58Mb document for more information: "A Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae." Today, higher oil prices and greater concern over CO2 should make the pursuit of microbial derived biodiesel an obvious choice.
Comments
I think you mean hygroscopic when describing the disadvantages of Ethanol.
Posted by: Michael | August 16, 2008 4:41 PM
Very interesting. This is basically solar power, but biological - and producing fuel instead of electricity. It seems to make a lot more sense than ethanol, especially since harvesting and processing would be simpler.
Posted by: WCG | August 17, 2008 8:33 AM
Sounds like an interesting technology but it's always good to keep in mind what might be the feasibility of integrating this into the landscape. How many square feet of earth surface would this process need to occupy to make a significant contribution to our energy supply? Can it be done on land that is not usable for growing crops so that we don't limit food production? How much water is consumed? What areas of the country would support it? And of course, what is the net gain in energy when all the inputs are accounted for?
Posted by: colluvial | August 17, 2008 8:28 PM
Colluvial, anything we use to replace oil is going to have a huge footprint. Every option - except nuclear - is just too diffuse. We'll inevitably be talking about massive wind farms, huge solar arrays, fields of plants grown for ethanol, etc. - even for a relatively small slice of the energy pie.* You're right that these things must be kept in mind, but this technology certainly seems to have a lot more promise than something like ethanol.
(*Of course, solar panels on residential roofs would use 'wasted' space, and I'd certainly like to see that, but localized energy production would be so variable that this would almost certainly have to be matched with massive installations somewhere.)
Posted by: WCG | August 18, 2008 8:47 AM
Can you grow those things in sea water?
Posted by: tuatara | August 18, 2008 11:48 AM
colluvial -
As far as I know, this process can use desert land and seawater; indeed, deserts have advantages in terms of sunlight. In theory, sewage/agricultural runoff can be used to help fertilise the bacteria as well.
Replacing all current fuel oil use is probably not possible; however, if we consider that the majority of land transport can be electrified (either electric cars or electric trains) reasonably easily, and heating oil replaced with electricity, we could reduce oil requirements by perhaps 60-70%.
If we also add in processes such as making methanol from currently-landfilled carbon based materials (Wood, paper, plastic etc), we could take the biodiesel from algae requirement down to perhaps 15-20% of today's oil usage figures, without any drastic lifestyle changes. That would still require a large area, but not such a drastically large area.
Posted by: Andrew Dodds | August 20, 2008 4:37 AM