Wood processing waste is a biofuel source, accordding to the Energy blog which says
Adding a little coal and processing the papermaking industry's black liquor waste into synthesis gas is a better choice than burning it for heat, improves the carbon footprint of coal-to-liquid processes, and can produce a fuel versatile enough to run a cooking stove or a truck, according to a team of Penn state engineers.
That's got to be one of the better ideas for biofuels, taking a waste product and doing something useful with it, even if in volume terms it is limited, compared to oil.