The per hectare reductions in global warming potential achieved by replacing gasoline with poplar derived ethanol are
calculated using Equations (1) and (2).
Over the lifespan of the proposed poplar plantation (21 years) 300 t of bone dry chips would be harvested per hectare. Using the EP this will produce 93.6 m3 of ethanol.
Averaged over 21 years, a hectare of land would produce 4.46 m3 or 104 GJ (GJ) of ethanol annually.
The GWP for 104 GJ of ethanol is 0.73 t and the GWP for 104 GJ of gasoline is 9.3 t.
Using a hectare of land to grow poplar, therefore, would result in an annual GWP savings of 8.6 t ha1 when ethanol is produced with the ethanologen process.
By comparison, assuming the same poplar chip yield of 300 t over 21 years, the AP would produce 170 m3 of ethanol, with an average annual ethanol yield of 8.1 m3 or 190 GJ of ethanol.
The GWP of 190 GJ of ethanol produced by the AP process is 9.1 t and the GWP of 190 GJ of gasoline is 17 t.
If the ethanol from the AP process replaced gasoline for fuel use it would have a GWP savings of 7.9 t ha1.
In contrast to using the unit energy basis, the GWP savings of the acetogen pathway on a per hectare basis is similar to
the GWP savings of the ethanologen pathway.