Biodiesel isn't that bad. In a vehicle it just requires a newer model. The main reason being that bio-diesel requires earlier combustion phasing for peak efficiency. So you need a modern on-board computer to make the changes. Kinda like how new vehicles can run premium or down to 87 octane.
In a jet engine these issues don't really matter. Biodiesel makes 67% less hydrocarbons than regular diesel which is a HUGE plus, however it does create more NOX which in airplanes I think is the biggest issue. At altitude the sun reacts with NOx causing a chain reaction that produces O3(ozone) which causes birth defects, respiration issues, and (I'm not 100% on this) I think it even kills the immune system. I have no clue if putting O3 out at higher altitudes is a good or a bad thing. They are always complaining about the ozone layer so perhaps in the upper altitudes it helps.
Diesel has on average= 129,500 btu/gal and a density of .85g/cm3
B100(100% biodiesel)= 118,296 btu/gal with a density of .88g/cm3 (8.65% less power producing ability while weighing 3.53% more than conventional No. 2 diesel)
B20 = 127,259btu/gal @ .856g/cm (1.73% less power producing ability while weighing only .7% more)
There's also a B2 blend but there's no point in it. 1-2% could barely be noticed if at all. In automotive diesel there can be a 15% variance in the btu/gal depending on the manufacturer and time of season. When I lived on the Mexican border I'd fill up over there for half the price and get 23mpg going 80mph in a 4dr Dodge diesel :O
It will be interesting to see what data they manage to produce from the test. I'd like to see a comparison of the reduction in hydrocarbons vs the reduction in fuel economy. If we get a 5-10%+ reduction in hydrocarbons with only a 1-2% loss in fuel economy that would be incredible. My math says that 20% BD could reduce hydrocarbons by 13.4%. 1-2% loss in power for a 13.4% decrease in hydrocarbons is amazing if it pans out that way. On the other hand I could have easily screwed the math up by making it too easy.