Page 64 - Advances in Eco-Fuels for a Sustainable Environment

Ecofuel feedstocks and their prospects 41

overall health of a region’s natural resources). The loss of plant life also means a loss
of valuable CO 2 scrubbers: native forest is almost always better at removing CO 2
from the atmosphere than a biofuel feedstock, as the CO 2 remains trapped and is
never released by fuel burning. This would release vast amounts of sequestered car-
bon, and create a carbon debt that could take centuries to repay. The second damage
is done by the carbon debt just created. Energy is needed to deforest and prepare an
area for farming as well as to plant crops. All this produces emissions and puts the
region at a net positive GHG production before a single liter of biofuel is even pro-
duced. Energy is also required for harvesting and replanting the crop: estimates
showed that deforesting could produce a carbon debt that could take up to 500 years
to repay. Using virgin land for biofuels, even if no food was ever grown, is the equiv-
alent of potential ecological bankruptcy. Finally, changing land to agricultural status
means that fertilizers are likely going to be used. Fertilizers require notable energy
(and GHG emissions) for their production and are subject to runoff and agricultural
pollution generation. Increasing farmland areas is likely to damage surface waters,
requiring investing more energy into treatment facilities and other mitigation
strategies.
When indirect land-use change effects started to be considered in the GHG
accounting of biofuels, GHG overall emissions savings from biofuels were rec-
alculated as [9]:
Corn ethanol from 20% to +93%
-
Cellulosic ethanol from 70% to +50%
-
where negative and positive values are intended compared to fossil fuels. The solution
is to identify feedstock that could grow more rapidly and with less water and nutrient
needs. Some types of microalgae, genetically modified, could satisfy these require-
ments. Biogas (and some other fuels) are still a concern, when made directly from
animal or agricultural/forest waste, despite the environmental benefits connected to
waste disposal and energy recovery. Biofuel production could use anywhere from
2 to 84 times as much water as fossil fuel production. Table 2.11 shows embedded
water use (in L/km) for motor vehicles fed with different fuels. Some feedstock, such
as cellulosic ones (generally leftovers of foodcrops harvesting), use much less water,

Table 2.11 Water use (L/km) for different fuels
Fuel Source L H 2 O/km (Car) L H 2 O/km (Truck)
Corn 667.3 1047
Grain 0.40 0.66
Cellulosic biofuel 0.61 0.99
Petroleum 0.09 0.17
Oil shale 0.19 0.50
(Data from: Sandia Natl. Laboratories, US DoE.)