At least it's hypothetically possible to create with less net carbon impact than fossil fuels. It still has a long way to go, but we've got to invest in things that aren't practical right now if we ever want aviation to decarbonize.
The most common method of making biodiesel that I know of involves fermenting farming byproducts, namely corn stalks and manure.
However, it still produces CO2 when it combusts.
Yeah but how much energy does it take to keep the ferment going vs how much do you get out of it? Is it scalable to meet world demand? Remember that is basically what dino oil is but with millions of years of energy input from the heat and gravity of earth.
Fermentation is a natural process, so there's no energy input to the process. As for output, you get almost the same energy density as standard diesel, and some excellent fertilizer. For a farming area, it's very self sustaining. Farmers bring their excess crop waste and manure, they get fuel and fertilizer in return. Also, the methane that off-gasses during fermentation is collected and burned to supplement the power grid.
Considering it's mostly being used in this application, it works very well. However, I can see it falling way behind if scaled for widespread use in industrial and non-argricultural uses, where dedicated crops would be grown and harvested. Regardless, it's a good way to cut down demand for standard fuel products for areas that can sustain a large biofuel digester.