WTF Are Fourth-Generation Biofuels?


Have biofuels been around long enough for there to be four generations of them? Those in the biofuel industry think so. Scientists at the University of Essex have discovered a new mechanism that regulates the process of carbon fixation in plants. The research, to be published today in the Proceedings of the National Academy of Sciences, could lead to improvements in so-called “fourth-generation” biofuels by letting scientists design feedstocks that capture more carbon (hat tip to Biopact).

This follows Craig Venter’s statement last week that his company, Synthetic Genomics, will produce fourth-generation biofuels in as little as 18 months.

There’s been a great deal of debate recently over first-generation, or food-based, biofuels. Meanwhile, a breakthrough to commercialize second-generation, or lignocellulosic, biofuels has yet to materialize. So how are we already jumping to the fourth generation? We’ve broken down their evolution below, including making note of any related startups.

Biopact Fourth generation

First Generation:
First-generation biofuels rely on food crops as their feedstock. Corn, soy, palm and sugarcane all have readily accessible sugars, starches and oils. So brewing them into biofeuls simply involves either fermenting the sugars or chopping up the fatty oils through transesterfication.

The problems with first-generation biofuels are numerous and well-documented in the media, ranging from net energy losses to greenhouse gas emissions to increased food prices.

Most biofuel startups are not working with first-generation feedstocks but biofuel distribution startups, such as Propel Biofuels and Conserv Fuel, are working almost exclusively with food-based biofuels because that’s all that’s currently available.

Second Generation:
Second-generation biofuels use lignocellulosic biomass as feedstock, among them dedicated biofuel crops like switchgrass and agricultural residue such as corn stalks. Using specially designed microorganisms, the feedstock’s tough cellulose is broken down into sugar and then fermented. Alternatively, a thermochemical route can be taken whereby the biomass is gasified and then liquefied, a process known as “biomass-to-liquid.”

A lot of venture funding is going into second-generation biofuels startups as they race to develop a single, cost-effective process for producing biofuels. Kior is working on their “biomass catalytic cracking process” while Coskata claims they can produce ethanol for $1 a gallon using old tires as a feedstock. Mascoma is working to build a “super bug” that would digest lignocellulosic feedstocks while ZeaChem plans to tap poplar trees for fuel.

Third Generation:
Rather than improving the fuel-making process, third-generation biofuels seek to improve the feedstock. Designing oilier crops, for example, could greatly boost yield. Scientists have designed poplar trees with lower lignin content to make them easier to process. Researchers have already mapped the genomes of sorghum and corn, which may allow genetic agronomists to tweak the genes controlling oil production.

Monsanto and ADM have been developing genetically modified cultivars for years but amid intense competition and anti-GMO criticism are usually mum about their research. Arborgen is a startup working to make trees by design for biofuel and timber purposes.

Fourth Generation:
Fourth-generation technology combines genetically optimized feedstocks, which are designed to capture large amounts of carbon, with genomically synthesized microbes, which are made to efficiently make fuels. Key to the process is the capture and sequestration of CO2, a process that renders fourth-generation biofuels a carbon negative source of fuel. However, the weak link is carbon capture and sequestration technology, which continues to elude the coal industry.

Venter says his Synthetic Genomics can make moot the issue of CO2 capture. His company plans to combine the processes of feedstock growth and fuel processing by designing organisms that will inhale CO2 and excrete sugars. We’ll see if these potentially world-saving bugs become a reality in the next 18 months.


Jeremy Abramowitz

Crank! I was tooling around on the Internets reading about different generations of biofuels and stumbled upon your work. It is very nice to see that you are still involved in the business and continuing the good work you did in developing the Big Green Bus and other environmental initiatives from our student years. I work in technical programs for the Solid Waste Association of North America so my work involves research on waste-to-energy systems that are very similar in scope and process to advanced biofuels.

As far as third vs. fourth generation biofuels I would assume the biggest difference is the modification or engineering of the biogenic feedstocks themselves. So in a third generation system the distinguishing feature is the use of photobioreactors and other systems to cultivate autotrophic microorganisms, while a fourth-generation system might be characterized by an algae or cyanobacteria breeding program to select for especially useful qualities such as high hydrocarbon content or enhanced carbon storage. A photobioreactor can also be injected with exhaust, produced by combustion for energy production, for CO2 enhancement to as a way of increasing the efficiency of any fuel-based system. In other words: third- and fourth-generation biofuel systems can be retrofitted onto combustion power plants for CCS and an additional layer of fuel production with zero negative impact on existing sequestration (from accumulation in forests, soils, wetlands etc)

Kudos and keep up the good work!

-Jeremy Abramowitz


Third generation biofuels are considered to be produced from Algae biomass and not modification of feedstock sources. What you propose to be third generation biofuel is still biofuel from cellulose even though the source has been modified. Therefore I think that calling the further modification of these cellulose producers to store more carbon can still be considered second generation. Fourth generation biofuel could be biofuel from a different source such as the conversion of chitin from shellfish waste. Chitin is after cellulose the second most abundant biomolecule on earth.


Rory’s question is the same as mine.

The carbon is going into the sugars which then go to EtOH, Butanol, or other carbon compounds. I am not certain how this is anything but zero sum at best.

I have seen mention of “below soil” carbon sequestration which I am imagining is root biomass that is left behind and being added into the equation to try to semantically offset the carbon that is being pushed downhill into more combustion.

Every moment we burn fossil fuels (ancient carbon sequestration) we skew the equation further in the direction of increased carbon in the atmosphere and climate warming. Any use of biofuels (nascent carbon sequestration) is simply recycling the carbon we have on the surface of the earth. Because its not going into long term living beings (old growth forests) and is being pumped through the feedstock-to-fuel cycle very quickly, there is really no appreciable “real” impact to this very temporary carbon sequestration. Hope that makes sense.

Any serious biofuel discussion (development, investment, etc) should start from one simple question (mantra) – where is the nitrogen going to come from.

Muhammad Iqbal

I’m sorry sir, but I think you forgot about the accummulation which occurs within the plants itself. When the plants do carbon fixation, they don’t convert all of this carbon to sugar, they also accummulate them as their biomass in a form of cellulose, lignin, protein, pigment, etc. So,the total mass balance of carbon at the atmosphere still reduced of course.

Muhammad Iqbal

I’m sorry Mr Nika, but I think you forgot about the accummulation which occurs within the plants itself. When the plants do carbon fixation, they don’t convert all of this carbon to sugar, they also accummulate them as their biomass in a form of cellulose, lignin, protein, pigment, etc. So,the total mass balance of carbon at the atmosphere still reduced of course.


Green energy is definitely the best solution in most cases. Technology like solar energy, wind power, fuel cells, zaps electric vehicles, EV hybrids, etc have come so far recently. Green energy even costs way less than oil and gas in many cases.


Wow, you got me raging on the title, but this is actually a really good read. In Germany bio-fuels have been mainstream since 10 years at least. The fact that we cannot simply fuel up on bio-diesel here is still crazy. Anyways, we are indeed on the fourth generation, and North America is just a little bit slow!!!! (sorry to hurt any feelings)

Rory Gawler

By the way, I think this is a comprehensive and highly interesting and relevant article.

Rory Gawler

Would feedstocks designed to inhale additional carbon be higher in energy content as well? Otherwise, wouldn’t they just slightly delay climate change as all the extra carbon they inhaled was exhaled during their combustion?

What are Mr. Venters direct-to-sugar plants going to do with this carbon? It doesn’t just disappear…

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