Essentaily made from veg oil, run through a process called transesterification that exchanges the alkoxy group of an ester compound with some alchohol and gains a proton along the way. The whole process almost halfs the molecule size, which makes it a little thinner, and gaining the proton makes it more reactive.
It can be mixed with DERV, in fact all diesel from grangemouth has a small percentage already. This is a blend, they usually start at 5% and go as high as 100%, which as suggested would be pure bio diesel.