I know they make a point in reasoning "why not landfill?" but I have to wonder if "injecting our magic bio-oil deep underground" just sounded better to the VCs vs "we we just friggin' buried the corn husks."
On a serious note...that's not a bad idea. I will need to find out why that's the case (although I imagine it's something to do with the pyrolysis leaving a more stable and predictable carbon-rich mass rather than leaving the degradation to nature)
"Others are working on this method. The landfills are expensive to dig, the geology is critically important, and we don’t believe the capacity to be as scalable or as permanent as injecting carbon-containing liquid into deep geological storage. The conversion of biomass into bio-oil via pyrolysis results in a liquid form with a higher carbon density, and is more easily handled, transported, and injected into existing wells."
Burying biomass produces methane as it anaerobically decomposes. I'd imagine that capturing that is fairly challenging compared to (essentially) burning the biomass and separating out the carbon.
Biomass can be pyrolized to produce flammable gas, charcoal/biochar, "wood vinegar", and a few other byproducts in a process that produces surplus energy. As long as you have biomass feedstock coming in, you can produce highly concentrated solid or liquid carbon on the far side and get energy out as power.
Biochar, the solid product of pyrolized biomass, is considered a beneficial soil amendment (it's basically elemental carbon -- like what you'd get in a charcoal filter). It's probably not a good idea to breathe it though.
I'm not sure about bio-oil specifically, as it contains much more of the tar-like compounds. It's likely it contains benzene and other compounds. I found this in a cursory google search: https://www.nrel.gov/docs/fy07osti/37779.pdf
Notably the dose makes the poison as well. If just "helps plants grow" was enough to be an environmental good then fertilizer run off would be a good thing.