Facts about cooking oil fuel are pretty slippery
You produce a secondary bio fuel from cooking oils.
Vegetable oils have a much lower energy output and you have to burn more to go the same distance as other fuels. So larger quantities are needed to produce an equivalent amount of energy. So even though its Co2 emissions are lower than diesel it requires that you burn much more of it which makes the Co2 component almost equivalent in the end.
It requires carbon intensive machinery to produce the initial product. It is exactly like the upstream and downstream Co2 calculations the enviros love to throw out in regards to oil and gas production. There is a huge cost of the initial investment to make the stuff just like a refinery has huge costs. It impacts crop prices for foods and it put a lot of pressure on water resources. It also produces CO2 emissions and it is a carbon based fuel. It also produces particulate as big as diesel fuels which makes it a dangerous choice for asthmatics, seniors, people with heart conditions or lung conditions or people with suppressed immune systems.
Saying it is a clean energy alternative with a tiny carbon footprint is not true. It is an alternative and only marginally better IMHO than actual diesel. Nevertheless that is why some chose to use that fuel. Fair and dandy but use it without shady carbon trading and governmental transfer of taxpayers funds to support it.