We could use External Combustion engines maybe ?
they are not so efficient but they can use anything as fuel.
As a side note I once read about a plastic surgeon in Beverly Hills who had an old mercedes diesel and he used the fat he got from liposuctions to power it.
>>I once read about a plastic surgeon in Beverly Hills who had an old mercedes diesel and he used the fat he got from liposuctions to power it.
I hear that liposuction fat makes good soap, too.