A recent post in the Technology Review “A Biofuel Process to Replace All Fossil Fuels.” (Image Source: JouleBio.com)

Previous study by the US DOE Aquatic Species program found a few things that are relevant. While the process and outputs differ, some of the limiting factors are the same. I truly hope Joule Bio can deliver on their claims, but I am personally skeptical for a few reasons:
- The theoretical maximum for open pond algae to biodiesel is around 15,000 gallons per acre
- Anything but open pond is prohibitively expensive for mass production
- As organisms excrete more fuel into the environment, excretion displaces nutrient sources
- Organisms need energy to reproduce, and converting CO2 to hydrocarbons also takes a lot
Theoretical maximums can certainly be improved using new technologies and engineering the organisms so their metabolisms are on overdrive is one way to do it. However, there are a number of limiting factors, including sunlight, CO2 and nutrients. As closed systems become stacked higher, a lower percentage of the organisms receive sunlight at any given time. The problem can be addressed by pumping fluids containing organisms to and from the surface. However, growth is still limited by sunlight. Additional light sources can be introduced, but they also require energy, and additional money to power.
There is nothing inherently expensive about closed bioreactors, but scaling them to large areas is much more expensive than an open pond. Similar tests at Dow aim to produce up to 100k gallons of ethanol on 24 acres, which is still only a little over 4k gallons per acre, and less than the 5k gallons per acre the Aquatic Species progam actually achieved in open ponds.
A current technical barrier, which could possibly be overcome through genetic engineering, is that organism survival rate drops off as ethanol content goes up. The concept can be observed in fermentation of wine and beer, as the alcohol content increases, yeast dies off and alcohol content peaks. The National Renewable Energy Laboratory, which is working with some of these companies, is aware of the challenge (PDF, p5) and is working on producing “super-bugs” that can survive in harsh conditions. The research is promising, but as the desired alcohol content is excreted by the organisms, it displaces nutrients in the environment and further limits growth. The balance of inputs and outputs is one area still being studied, and the results will be dependant upon the organisms used.
One final reason for my pessimism about total output of the Joule Biotechnology approach is that creating hydrocarbons from CO2 is energy intensive. Even with the abundance of solar energy, if an organism puts too much of its energy towards its output, then it will not have as much energy to reproduce. Much of the reason algae has been investigated for biofuels is that it reproduces so quickly. Scaling to large numbers is easier when organisms reproduce quickly. In algae to biodiesel production, the oils from within the algae are extracted, which kills them off. Without high growth rates, expansion would not be possible. Fortunately, in the Joule Biotechnology approach, the products are extracted without killing off the organisms. However, as more energy goes to production, less goes to reproduction, limiting how fast production can scale.
These companies all have ambitious goals, but it appears that the numbers and claims are still too inflated. The most ambitious stated goal is by a company called Algenol that hopes to produce one billion gallons of ethanol a year. Based on current consumption [updated] of gasoline, which would be displaced by the ethanol, that’s still less than two thirds of gasoline consumption in the United States. Two thirds One third is certainly a significant proportion, but it will take years and major technology advances to come close to that, and global consumption will continue to increase.
I do believe that with government subsidy, and potentially without, that some of these will eventually be profitable. However, I do not believe that any of these companies will come close to “replacing all fossil fuels.”
Update: New EIA numbers show consumption data was actually ~3.3 Billion gallons.