Imagine if instead of digging oil up out of the ground and refining it into gasoline, we could just have bacteria make it for us in a big vat somewhere. Since we would grow the food that the bacteria turn into gasoline, this would be a very low carbon fuel option that lets us keep the current internal combustion technology and the vast distribution system already in place. In other words, this approach would greatly decrease our carbon footprint with minimal retooling of the existing infrastructure.
The downside is that for now, the bacteria need the food we eat to make the gasoline. We got a taste back in 2008 and 2011 for what happens when we try to lower carbon emissions by using food to make biofuels—food price spikes and their accompanying riots. Ideally, we will want to be able to feed the bacteria stuff we can’t eat so that making gas doesn’t cause starvation.
This is all relevant because researchers from South Korea have engineered bacteria to make gasoline. Through a series of genetic tweaks and add-ons, they have coaxed the laboratory workhorse, E. coli, to make around 580 milligrams (mg) of gasoline per liter of culture. While this is an amazing bioengineering feat, 580 mg is as little as it sounds.
Using this handy calculator, it looks like there are 2.9 million or so mg per gallon of gas. A little algebra shows that we would need around 5000 liters of bacterial culture to get a gallon of gas. Even with the best gas mileage, this wouldn’t be competitive. And these researchers know it.
They claim that if they can boost the bacteria so that it makes 10 or 20 grams of gasoline per liter, then it will become competitive with gasoline obtained the old-fashioned way. They can get away with this still relatively low level of production because unlike oil or tar sands, the bacterial gasoline doesn’t need any refining. The bacteria produce it ready-to-go!
Getting from half a gram to ten or twenty grams will not be trivial and will probably need some significant breakthrough. These are hard to predict which means we can’t know if they can get bacteria to this level in a year, a decade or a century. But if it happens, it may be one piece of the puzzle in dealing with global warming while maintaining our current standard of living.
It is important to note that bacterial production of biofuels is not the only game in town. One of the most viable alternatives currently is biodiesel. It isn’t great in the cold but at around $2.00-2.50 per gallon to produce, it is getting pretty competitive with petroleum based diesel.
Right now large scale production of biodiesel suffers from the same issues as bacterially made gasoline—food has to be used to make it. The numbers I have seen are that it takes something like 7.6 pounds of soybeans to make a single gallon of biodiesel. Given that the U.S. uses around 60 billion gallons of diesel each year, it would take a whole lot of soybeans just to match our current needs. Keep in mind this number doesn’t include any increased diesel needs as more and more cars are converted to diesel.
Figuring out how this compares to the bacterially produced gasoline is no picnic! I tried a back of the napkin calculation to figure out how much food it takes for these bacteria to make a gallon of gas but it may be a bit off. Still, it does give a number that is probably in the right ballpark.
A little digging found that 3,360 pounds of corn can yield about 2000 pounds of a 90% glucose solution or about 1800 pounds of glucose. Since the researchers used 5000 liters of a 20 gram per liter culture to get one gallon of gas, that means each gallon of gas would take 100,000 grams of glucose. A little algebra and we come up with 220 pounds of glucose per gallon of gas which translates to a mind boggling 411 or so pounds of corn. Suddenly biodiesel is looking pretty reasonable!
If they can really get the bacteria to produce 20 grams of gasoline per liter of culture, the amount of corn needed for each gallon of gas falls to 11.9 pounds. This is getting pretty close to the ball park of biodiesel but is still an awful lot of corn.
Both the soybean based biodiesel and the bacterial based gasoline simply need too much food to be useful as a substitute for petroleum based diesel and gasoline. Scientists need to find ways to use inedible plants to make biodiesel or to feed these bacteria. This is obviously an active area of research with great strides being made in turning cellulose into the gasoline additive ethanol. If scientists can get similar results with a cellulose to glucose conversion, then this bacterially produced gasoline may yet let us live happily ever after.
Learn more in this great article on other fuels that will not require a change in infrastructure.