You can ferment it in bacteria.  You can subject it to outlandish temperatures and pressures.  But however you produce biofuel, one thing is constant -- you need a supply of carbon, the "feedstock".

I. Switchgrass == Environmental Threat?

One leading candidate for widespread use as a biofuel feedstock is switchgrass.  Fast-growing and hardy, switchgrass quickly produces a great deal of biomass.  But a new study by the University of Illinois reveals a potential downside -- switchgrass' growth comes at the cost of soil moisture.

Switchgrass is apparently so effective at sucking water out of the ground that it could cause adverse affects to other human crops, as well as local ecosystems.  Praveen Kumar, the Lovell Professor of civil and environmental engineering at the University of Illinois states, "While we are looking for solutions for energy through bioenergy crops, dependence on water gets ignored, and water can be a significant limiting factor.  There are many countries around the world that are looking into biofuel energy, but if they are adopting these (large grasses) into their regular policy, then they need to take into account the considerations for the associated demand for water."

The study examined transpiration -- the loss of water through plant pores.  Ultimately switchgrass and another fast growing grass, Miscanthus, transpire at a higher rate than corn (the most widely used ethanol biofuel crop) and thus pull water from the soil at a faster rate.  This dries the soil and increases humidity.

The researchers also used a predictive model to study what would happen if the predictions of global warming were realized.  What they found was that while higher carbon dioxide levels decreased the transpiration rate by allowing the plant to open its pores to the air less frequently, higher temperatures negated this affect by increasing the rate of water loss while the pores were open.  Overall, the predicted affect was even higher rates of water loss.

Regardless of whether the warming scenario occurs, however, the study raises concerns for the viability of switchgrass and Miscanthus as biofuel feedstocks, particularly in drought-prone regions.

The study was published [abstract] in the peer-reviewed journal PNAS (Proceedings of the National Academy of Sciences).

Of course, the pro-corn, anti-grass bent should be taken with a grain of salt.  The University of Illinois has a long-standing relationship with the corn ethanol community, which would be displaced in a move to switchgrass cellulosic ethanol.  While this particular study was funded by a National Science Foundation grant, given the overall financial situation, it's possible that researchers at the University of Illinois could feel incentivized to find downsides of switchgrass and the upsides of corn.

II. Algae Could be the Cream of the Crop

That said, the University of Illinois, in a separate study, is promoting a fascinating biofuel alternative to both corn ethanol and switchgrass -- seaweed.  Recent efforts by the U.S. Marine Corps have heated up interested in algae- and seaweed-based biofuels.

The new study looks at how to speed up the slow process of fermenting red seaweed biomass to produce biofuel.  Currently Saccharomyces cerevisiae -- commonly named yeast -- is the leading candidate for fermentation as it has genes which code for proteins capable of digesting both galactose and glucose -- the two primary sugars in red seaweed.  However, wild-variety yeast "eats" glucose before it will eat galactose, making the fermentation process slow, and thus, ultimately, more expensive.

By introducing a new sugar transporter and enzyme that breaks down cellobiose at the intracellular level via a bit of gene splicing, the team was able to create a strain of yeast that simultaneously digests galactose and glucose, cutting the production time of red seaweed-derived biofuel in half.

Yong-Su Jin, an assistant professor of microbial genomics, compared the development "to a person taking first a bite of a cheeseburger, then a bite of pickle. The process that uses the new strain puts the pickle in the cheeseburger sandwich so both foods are consumed at the same time."

Professor Jin says that the pre-treatment process to break down seaweed into cellobiose -- glucose pairs -- and galactose is considerably less toxic than many of the potential processes to break down cellulose from terrestrial crops.  Furthermore, he says that red seaweed has several other advantage as well, including its higher biomass-per-unit-area density, its higher rate of carbon fixation than terrestrial biofuels crops, and its ability to grow in the sea, thus escaping land-space constraints.

The researcher selected the red variety (Gelidium amansii) of seaweed as it’s a fast-growing variety found in abundance in one very space-constrained region -- Southeast Asia.

The study on the work was published [abstract] in the peer-reviewed journal Applied and Environmental Microbiology.  The study follows work earlier this year published [abstract] in PNAS, which saw Professor Jin's team introduce pathways for simultaneous digesting of xylose -- another plant sugar -- and cellobiose into a yeast strain.

Together the studies paint an interesting picture.  Switchgrass is potentially undesirable in arid regions and in space-confined regions.  However, many of these same regions border the sea.

So for regions like the Southeastern United States, Southeast Asia, the Middle East, and Japan, growing biofuels in the sea might be the wisest approach of all.