Feasible biofuel?

As the fuel price soars, it seems difficult to achieve the transition to more sustainable and renewable energy supplies without using biofuel for at least a portion of our fuel consumption. While we have a range of technically possible biofuel solutions, they are all more or less unsustainable, some are even wasteful and/or dangerous. In my opinion, the biofuel alternative that is practical should at least have a few characteristics:

First and most importantly, the energy invested in the whole life cycle of such biofuel should not exceed what human can extract from it. This seems natural yet many alternatives reported in the past year failed to meet this criterion. Some appear to have higher output than their fossil counterparts but the actual result is opposite if one count the energy cost of collection, extraction and transportation in.

The second and equally important characteristic is that the raw material had better be a byproduct, or at least the growth of the raw material does not reduce land availability for food production. The rapid adoption of biofuel crops in some countries may have contributed to rapidly increasing food prices worldwide.

The effort to increase unit productivity of biofuel crops should be responsible and do not cause ecological problems. It is worried that some biofuel species may be invasive, rendering the food production problem more serious. Biofuel based on algae without effective control may be a problem for the marine ecosystems. It is also possible that economic incentives urge people to transform previous landuses to new ones that are not so sustainable, or destroy key habitats.

And pollution, though an old problem already, should not be enhanced by biofuel production. Many kinds of biofuel boast less pollution in combustion compared to fossil fuels, but pollution in production and exhausts still need attention and auditing.

At present there is few biofuel that meets all these criteria, and that's why I am against mass adoption of them. For transitional energy alternatives, nuclear may be a better choice.