Saturday, March 06, 2010

Kudzu Power

For several years I've mused that if only we could find some efficient way to make ethanol from Kudzu (the incredibly fast growing invasive weed that has taken over much of the southeastern US), we could stop importing petroleum, vastly improve many ecosystems and tremendously improve the US economy, all in one swell foop. I didn't take this idea very seriously. It appears that somebody else has. Consider the following abstract from a recent volume of the journal Biomass and Bioenergy:

We determined the amount of standing biomass of kudzu (Pueraria montana var lobata) in naturally infested fields in Maryland and Alabama, USA. At each site, we evaluated the carbohydrate content of roots, stems, and leaves. For a third site from Georgia, we evaluated the carbohydrate content of kudzu roots of varying diameters. Belowground biomass in Alabama exceeded 13 t ha−1, and contained an average of 37% fermentable carbohydrates (sucrose, glucose, and starch). Roots from Georgia of all size classes contained over 60% fermentable carbohydrates. Biomass and carbohydrate levels in roots from Maryland were low compared to plants growing in Alabama and Georgia, producing 5 t ha−1 of roots with 20% non-structural carbohydrate. Stems from Alabama and Maryland contained 1–3% carbohydrates. Based on the yield and carbohydrate content, we estimate wild kudzu stands in Alabama and Georgia could produce 5–10 t ha−1 of carbohydrate, which would rival carbohydrate production from maize and sugar cane fields. If economical harvesting and processing techniques could be developed, the kudzu infesting North America has the potential to supplement existing bioethanol feedstocks, which could be of significance to the rural economy of the southeastern USA.

Further consider this economical processing technique, from next month's PNAS:

Abundant plant biomass has the potential to become a sustainable source of fuels and chemicals. Realizing this potential requires the economical conversion of recalcitrant lignocellulose into useful intermediates, such as sugars. We report a high-yielding chemical process for the hydrolysis of biomass into monosaccharides. Adding water gradually to a chloride ionic liquid-containing catalytic acid leads to a nearly 90% yield of glucose from cellulose and 70–80% yield of sugars from untreated corn stover. Ion-exclusion chromatography allows recovery of the ionic liquid and delivers sugar feedstocks that support the vigorous growth of ethanologenic microbes. This simple chemical process, which requires neither an edible plant nor a cellulase, could enable crude biomass to be the sole source of carbon for a scalable biorefinery.

This will, of course, take longer and be more complicated than anyone currently expects, but I'd be surprised if we don't eventually have industrial scale application of this technology, using many sources, including kudzu.


jte said...

Kudzu might come into play with the cellulosic processes, but how viable could it ever be to start harvesting the root mass? I know people harvest potatoes from below the surface, but kudzu isn't growing in nicely prepared agricultural fields. It's growing in and around everything else. That's not the kind of situation you want when you are doing industrial scale harvesting.

GreenEngineer said...

Yeah, apparently kudzu makes a pretty good forage crop too. And that avoids the problem of getting at the roots. (Another option would be to use the aboveground biomass for gasification as the first step towards fuel production. In that case, you don't care about cellulose vs. starch -- it's all just biomass.)

I don't think the problem with runaway kudzu is a lack of potential uses. There's just no mechanism for economically connecting the resource with a potential user.