Celebrity Death Match - Biodiesel vs. Bioethanol (Part I)

A fight for the ages, and it's being waged through the pages of Trends in Biotechnology!

In 2007, Yusuf Chisti published an opinion piece in Trends in Biotechnology with the title "Biodiesel from microalgae beats bioethanol" (see reference, below). In this article, Dr. Chisti laid out the rationale as to why we should seriously look at biodiesel from microalgae. In the abstract, Chisti states ...

Biodiesel from microalgae seems to be the only renewable biofuel that has the potential to completely displace petroleum-derived transport fuels without adversely affecting supply of food and other crop products.

Say it ain't so! You mean to say, that if we rely on food crops to develop ethanol ... we're going to adversely affect our supply of food? Who would've seen that coming?!?

Let's score it:
Yusuf Chisti: 1
Ethanol Lobby: 0

Figure 1 of the opinion piece lays out a conceptual system (see image below) for producing this microalgal oil for biodiesel. As you can see, not only does the algae have use as an oil source, the remaining byproducts can be used for anaerobic digestion. If you recall my earlier talks, anaerobic digestion produces methane. When this methane is cleansed of contaminants, it is indistinguishable from the natural gas (which is methane) which we use daily to heat our homes, produce electricity, cook our food ... and even some vehicles use as fuel.

And it doesn't stop there. If you use the methane/biogas for power generation (for sale on the grid, and to run the algae production process), you wind up with carbon dioxide. That carbon dioxide can be shuttled back to the algae biomass production area for re-use by the algae in photosynthesis. Very little carbon dioxide will be released into the atmosphere, and very little fossil fuel will be used to run the process. In essence making the system "carbon neutral, as Chisti states:

Ideally, the microalgal biodiesel can be carbon neutral, because all the power needed for producing and processing the algae could potentially come from biodiesel itself and from methane produced by anaerobic digestion of the biomass residue left behind after the oil has been extracted.

Biodiesel kicks bioethanols ass

This section of the opinion piece starts off looking at the algal biodiesel compared to sugarcane bioethanol because "sugarcane bioethanol can be produced at a price comparable to that of gasoline". Simply put, when considering similar levels of energy recovery, sugarcane ethanol produces less than half that recoverable from algal biodiesel (75 metric tons of biomass per hectare for sugarcane versus 158 tons per hectare for microalgal biomass).

So what's stopping us?

In short: economics. The technology, while there in part, is not there in force. However, if the demand were there for microalgal processing equipment, the costs in machinery would eventually come down. Another issue is that of drying technology. Drying (removal of water) is a huge energy cost and additional research into processes which can dry the algae cheaply are needed. Thirdly, further research into the genetics of algae is needed. Increases in production of algal oil metabolism would result in greater yields of oil, resulting in lower production costs per barrel of algal oil.

As Chisti explains:

At this price [$100/barrel], microalgal biomass with an oil content of 55% will need to be produced at less than ~$340/ton to be competitive with petroleum diesel. Literature suggests that, currently, microalgal biomass can be produced for around $3000/ton.

But don't lose heart! Chisti goes on to say:

This analysis disregards possible income from biomass residues. In addition, converting M tons of algal biomass to biodiesel is likely to prove less expensive than converting a barrel of crude petroleum to various fuels. Nevertheless, the assessment given here provides an indication of what needs to be achieved for making algal biodiesel competitive with petrodiesel. A high threshold is placed on competitiveness of microalgal biodiesel by comparing it with petrodiesel: none of the biodiesel being produced commercially from soybean oil in the US and canola oil in Europe can compete with petroleum-derived diesel without the tax credits, carbon credits and other similar subsidies that it receives.

So, we need to get the costs down. I don't think this is an obstacle that cannot be overcome. With the proper infrastructure put in place, to produce and then process large loads of algal biomass, the costs will come down. Further advances in technology will likewise increase oil yields and reduce costs even more. It's not as if the petroleum market dropped into our laps as a full-grown adult, did it? It didn't, and while it currently remains "cheap" and I say "cheap" in comparison to other technologies ... it won't always remain the most economically viable commodity. And that doesn't even begin to address the fact that oil is a matter of national security. The point is ... we need to get these other technologies online NOW, so when the petroleum bubble DOES burst, we have a suitable alternative. Chisti demonstrates that biodiesel from algal biomass can be a basket we can put our eggs into.

Or ... maybe not? [cliffhanger - See Part II)

References

CHISTI, Y. (2008). Biodiesel from microalgae beats bioethanol. Trends in Biotechnology, 26(3), 126-131. DOI: 10.1016/j.tibtech.2007.12.002