you're right- the CO2 is rereleased when you burn the biodiesel. But I would hardly call the proposition "snake-oil." You basically get two uses out of the CO2 (from the initial burning at the power plant and the consumption in the car) for the price of one.

I think you'll understand the point if you can answer this question: which fuel is better for the environment- biodiesel produced from the method mentioned in the article, or regular diesel?

I really don't see any difference between the CO2 produced from this biodiesel and any other biodiesel. With regular biodiesel you have no net CO2 emission since the CO2 emmitted from the car is more than absorbed by the CO2 necessary to create the oil. With the biodiesel created in the manner mentioned above, the CO2 absorbed from the  power plants is rereleased by consumption by the car, but no CO2 that would normally produced from non-biodiesel consumption is released, meaning the net-emmission is the same as emission just from the plant, so it is as good as regular biodiesel.

The mathematical logic behind this is pretty simple:

regular biodiesel is like 0 + - 1 (CO 2absorption from algae) + 1 (release from car burning) = 0 (no net emission)

this biodiesel is like 1 (power plant emmision) - 1 (absorption) + 1 (release) = 1 .

Use of regular fuel is like 0 + 1 = 1 (net CO2 release).