I don't claim any expertise in biofuels! But Ben's question about the relative merits of ethanol and biodiesel is interesting and important.

Clearly there are lots of interrelated issues, some of which are particular to geographic regions. Because there are many economies of scale involved, governments often take a position favoring either biodiesel or ethanol.

From what I've gleaned, Nigeria takes a position which leans towards ethanol. One of the issues is that gasohol, that is a formulation of gasoline and ethanol requires engines which will run on them. Many vehicles already on the road are flex-fuel, they can run on gasohol.

Cassava can be used as a feedstock for biodiesel, but it requires a process called Thermal depolymerization which among other things requires heating the feedstock to high temperatures under pressure. So it's a relatively capital intensive process. It should be noted that seed oil production on a scale to produce biofuels is also a fairly capital intensive operation.

As Ben points out the operation under consideration is a relatively small capital affair. Ethanol can be made from cassava in this sort of enterprise. Ethanol also fits in with the Nigerian energy strategy. However there is concern about the ability of Nigeria to increase production of cassava and sugar cane to meet their targets and the impacts upon the food supply.

Part of the calculation about ethanol is the anticipation of the development of enzymes to break down cellulose to render sugar for alcohol, so instead of the kernels of maize being used, the stocks might be. Cellulosic alcohol is something much studied. Both Canada and China have plants producing cellulosic alcohol presently, but the efficient processing of cellulose is yet to be perfected, and certainly isn't a small-scale enterprise.

Biodiesel is generally made from vegetable oil. People in America eat so many fried foods that the waste oil from cooking has actually jump-started interest in making biodiesel here. Obviously a car which runs on gasoline will not run on diesel and vice versa. However there are many diesel engines, and other devices which operate using biodiesel as fuel. So biodiesel is a very useful fuel and it has the advantage of requiring relatively less energy to produce than ethanol.

With a supply of vegetable oil it's not a terribly capital intensive process to make biodiesel. However processing soybeans, rapeseed, and other oil bearing crops into oil on an industrial scale is a capital intensive enterprise.

It is not surprising to me that Nigeria as an oil producing country would favor the development of ethanol as part of their energy policy. It fits well with the existing delivery mechanisms as well as oil company objectives. Implementing this policy also impacts Nigerian agricultural policies; for one thing they need to grow more cassava.

On a small scale, even in Nigeria, it would seem that either ethanol or biodiesel could be an attractive enterprise given the right alignment of factors. Seed oil production is key to biodiesel. Ethanol can be made from a variety of crops which yield sugar, eg. cassava, sugar cane, sorghum, etc. My, admittedly ignorant, hunch is that there are fewer obstacles in the road for ethanol production in Kaduna than there are for biodiesel.