Hang on a second...
My initial reaction to "Bio fuels"... is to wonder if you mean, LPG, fuel oil, diesel, etc? Since hydrocarbons are biological chemicals they would technically count as "bio-fuels".
I'd assume something but I actually have no idea what "bio fuels" are, so I guess you'll have to educate me!
As an aside, I'm considered modelling a sewage works as an industry on a layout. Although not many of them were ever rail connected, they do have a potentially rail-transportable product output, which is essentially dryed biosolids (dead plants, mud, faeces, etc.). This is then taken to an incinerator at a landfill. Might be a good small-time branchline operation, switcher-only motive power, trains being no more than four to five freight cars long.
If you're dedicated enough to modelling this concept it can be very easily done. I've found the walthers wide oil-storage tanks useful in that respect - sawn in half they make a great pair of thickening/settling tanks. All you need to add is the central column, catwalk going between one edge of the tank and the central column, railings, and feed baffle ring (which surrounds the top of the central column) - there are more details you can add if you really want to, depending on how accurately you want to represent it, for instance; the feed pipe suspended underneath the catwalk. Some tanks, rather than having a central column, have an I-beam bridge going right the way accross, with a catwalk on top of the beams that usually gets as far as the center. To add a little variation in the tank sizes (Since they are not all one width) the Walthers tall and thin oil storage tanks will saw up into three small tanks. To make a percolating filter you simply build the sprinkling arms assembly, mount it on a central column, and fill the tank in with a dark grey or brown ballast. After that you need a river (to discharge clean water into) running by, on the banks of which you can put a few culverts. The loading spur for your railroad should run up alongside a storage building, attatched to which is the filter press building.
And if you want it to be really really prototypical, there are loads of websites on the internet that go into great detail about what exactly goes on in the sewage works process. My suggestion is to only model part of the sewage plant, the rest of it going off the edge of the board, in the land of the imaginary. Trying to model a whole plant will consume your budget and take up a whole lot of time as well as resources and board space!