Last time, I looked at research on the benefits of harvesting low-input high-diversity prairie plants as a feedstock for bioenergy. This week, practicalities and policies.
Biomass can be burned directly, alongside coal or some other fuel, as a source of energy for heat or power. But unless you’re running an old-fashioned external combustion engine, like a steam locomotive, that’s not much use for transport. Biodiesel is different, but for bio-ethanol you need yeasts, which convert starches and sugars into alcohol. There’s none of the nuanced fermentation of the wine-maker, though. Just a push for as much ethanol as possible. The problem is that both the starting material -- sugar -- and the final product -- ethanol -- can poison the yeasts. Wine-makers don’t care. Grapes are never so sweet that they harm the yeast, and while different strains of yeast will succumb to higher or lower concentrations of alcohol, the goal is to make a palatable product, not one that necessarily packs the most powerful punch. Bio-engineers want none of that. They want the most ethanol per batch. That means starting off with as much sugar as possible and ending up with as much alcohol as possible, and that's where the second Science paper comes in.
Gregory Stephanopoulos and his MIT colleagues could have laboriously tinkered with each step of the complex path that leads from carbs to booze. Instead, they upped the error rate as the yeast copied its DNA and then looked for better performance. Their approach was pretty clever. They created mutants of a gene called SPT15, which is an essential component in the mechanism that copies DNA. They expected the mutated SPT15 gene to induce further mutations in other genes by virtue of its role in copying. But many of those changes might be harmful and potentially lethal to the yeast. So they put the mutated SPT15 gene into a yeast that also contained a normal SPT15 gene. This way, the yeast’s machinery would continue to work normally, but if the mutated SPT15 resulted in any improvements in other genes, the yeast would survive and the researchers would be able to pick up the mutants.
And it worked (obviously, or I wouldn’t be here writing about it). The yeast now survived better in high sugar and high alcohol, and this improved performance was the result of changes to hundreds of genes. Picking on just the dozen or so genes most affected, none of them, on their own or in pairs, was enough to improve the yeast’s performance. It was the whole ensemble that played better together. The mutant strain ended up producing 70% more alcohol than the wild-type yeast, at a rate close to the theoretical maximum.
And the point is?
So, we have back to back academic papers that show firstly that a mixture of prairie grasses is a better source of biomass from all sorts of perspectives, and secondly that it is possible to make a much better yeast to turn biomass into bio-ethanol. Problem solved? No, not by a long way. On now to policy ...
The big isue with many biofuels is that, at least at the outset, they use the same feedstocks that people and their livestock use; edible plant parts. Some see it as a crime against humanity to convert food into energy. Better to give it to hungry people around the world. Others say that subsidizing farmers to grow biofuels is somehow less morally reprehensible than subsidizing them to grow food that is dumped on the world market, depressing local sales in developing countries. And these are only two of the more extreme positions. There seems to be at least as many views on biofuel policy as there are policy makers.
To the rescue rides IFPRI, the International Food Policy Research Institute, with Bioenergy and Agriculture: Promises and Challenges, the latest in a series of briefing documents. The booklet (downloadable here) contains 12 pithy briefs that look at bioenergy through several facets. Among the most complex is an analysis by Mark Rosegrant and his colleagues of the ways in which the development of bioenergy sectors might impact global food systems. IFPRI has something called the International Model for Policy Analysis of Agricultural Commodities and Trade (IMPACT -- a nifty acronym if ever there was one) that links a whole bunch of inputs with a whole bunch of outputs. Rosegrant set IMPACT to work on three possible scenarios:
- Aggressive growth in biofues with no change in productivity
- Cellulosic conversion -- the so-called second-generation of converting biomass into biofuel -- comes on stream in about 2015
- Aggressive biofuel growth with higher productivity and better conversion
For cassava, touted as an energy crop in the tropics, the results are staggering. The price of cassava under the first scenario increases by 135% by 2020. That puts it well beyond the reach of people who may prefer to eat it, “causing,” as the researchers drily note “sizable welfare losses to the major consumers of this crop, who reside mostly in Sub-Saharan Africa. ... If cassava is not profitable as a biofuel feedstock at today’s high oil prices, it certainly would not be at more than double the cassava price.”
Adding better conversion and improved productivity to the mix helps, but not much; cassava prices rise by 54%.
There are many more fascinating conclusions in IFPRI's brief, almost all of which suggest that the price of oil alone is going to be a minor factor in the growth of biofuels in developed and developing economies alike. That said, it is also clear that biofuels do offer benefits. With better feedstocks -- such as low-input high-diversity mixtures growing untended on degraded land -- and better conversion technologies -- such as improved yeasts -- the balance in favour of benefits shifts ever so slightly. The resurgence of interest in biofuels, prompted by oil instability and climate concerns, offers an intellectual feast as well as practical solutions. If I were younger, I’d be tempted to try and make it my living.