58
use is one of the advantages of LCA. However, analytical methods for this are complicated. There are two different strategies to evaluate apportion environmental
loads between the final products and its byproducts. Either practitioners can proportionally divide the burdens between output flows based on their physical (mass or
energy) content or economic value (called as allocation) or alternatively system
boundaries can be expanded to include additional credits related to the byproducts
displacement (called as system expansion).
Bagasse, a typical byproduct of sugarcane, is most commonly used for thermal
energy and electricity generation. Thus, environmental loads can be divided between
bagasse and ethanol based upon its energy content. This is a straightforward method
that guarantees stable outcomes, as physical properties are constant. However, the
allocation of physical properties may encounter criticisms, since environmental
loads are not necessarily proportional to products’ mass/energy content. Thus, practitioners can consider the expansion of the system boundary. When bagasse is used
as an energy source, it has the effect of replacing a fossil fuel. In the LCA, this effect
is evaluated as the avoided environmental loading from the fossil fuel. This is a typical case of system expansion.
If petroleum is replaced by a byproduct, the effect may be calculated as a reduction in the environmental loading caused by petroleum production. When electricity
is generated by a byproduct, the effect reduces the environmental load associated
with generating electricity. The substance replaced by a byproduct depends on the
geographic region, and because a number of different kinds of fuel are used in a
power grid, it is important to determine which fuels are replaced by the byproduct.
For example, if electricity is generated by a byproduct in a region where the grid
electricity is generated with coal, this leads to a large reduction in CO 2 , whereas if
electricity is produced from a byproduct in a region that uses hydroelectric power
generation or nuclear power generation in the grid, the CO 2 reduction effect is very
low.
As an example, we consider composting solid waste and substituting it for a
chemical fertilizer (Fig. 6.4). In this case, the system boundary must be expanded to
include fertilizer production. If the waste were not recycled through composting,
the waste would be landfilled, causing an environmental load such as methane emission, while energy would be used in the industrial production of chemical fertilizer.
Various environmental loads are caused by these processes. On the other hand, if
compost is produced from the waste, an environmental load is caused by this production, but the abovementioned environmental loads of landfilling the waste and
producing the chemical fertilizer are avoided. These calculations must be performed
so that the effectiveness of the compost matches the effectiveness of the chemical
fertilizer that is replaced. As the fertilizing effects of 1 ton of compost and 1 ton of
chemical fertilizer are not the same, adjustment is necessary in the calculation.
With biofuels, energy substitution by residues and replacement of chemical fertilizers are typical uses of byproducts. Large amount of residues are produced from
the conventional process for producing a biofuel from an energy crop. This residue
can replace large amount of fossil fuel. On the other hand, if the production yield is
raised by an innovative process, less amount of residue can be used to replace fossil
K. Hanaki and J. Portugal-Pereira
use is one of the advantages of LCA. However, analytical methods for this are complicated. There are two different strategies to evaluate apportion environmental
loads between the final products and its byproducts. Either practitioners can proportionally divide the burdens between output flows based on their physical (mass or
energy) content or economic value (called as allocation) or alternatively system
boundaries can be expanded to include additional credits related to the byproducts
displacement (called as system expansion).
Bagasse, a typical byproduct of sugarcane, is most commonly used for thermal
energy and electricity generation. Thus, environmental loads can be divided between
bagasse and ethanol based upon its energy content. This is a straightforward method
that guarantees stable outcomes, as physical properties are constant. However, the
allocation of physical properties may encounter criticisms, since environmental
loads are not necessarily proportional to products’ mass/energy content. Thus, practitioners can consider the expansion of the system boundary. When bagasse is used
as an energy source, it has the effect of replacing a fossil fuel. In the LCA, this effect
is evaluated as the avoided environmental loading from the fossil fuel. This is a typical case of system expansion.
If petroleum is replaced by a byproduct, the effect may be calculated as a reduction in the environmental loading caused by petroleum production. When electricity
is generated by a byproduct, the effect reduces the environmental load associated
with generating electricity. The substance replaced by a byproduct depends on the
geographic region, and because a number of different kinds of fuel are used in a
power grid, it is important to determine which fuels are replaced by the byproduct.
For example, if electricity is generated by a byproduct in a region where the grid
electricity is generated with coal, this leads to a large reduction in CO 2 , whereas if
electricity is produced from a byproduct in a region that uses hydroelectric power
generation or nuclear power generation in the grid, the CO 2 reduction effect is very
low.
As an example, we consider composting solid waste and substituting it for a
chemical fertilizer (Fig. 6.4). In this case, the system boundary must be expanded to
include fertilizer production. If the waste were not recycled through composting,
the waste would be landfilled, causing an environmental load such as methane emission, while energy would be used in the industrial production of chemical fertilizer.
Various environmental loads are caused by these processes. On the other hand, if
compost is produced from the waste, an environmental load is caused by this production, but the abovementioned environmental loads of landfilling the waste and
producing the chemical fertilizer are avoided. These calculations must be performed
so that the effectiveness of the compost matches the effectiveness of the chemical
fertilizer that is replaced. As the fertilizing effects of 1 ton of compost and 1 ton of
chemical fertilizer are not the same, adjustment is necessary in the calculation.
With biofuels, energy substitution by residues and replacement of chemical fertilizers are typical uses of byproducts. Large amount of residues are produced from
the conventional process for producing a biofuel from an energy crop. This residue
can replace large amount of fossil fuel. On the other hand, if the production yield is
raised by an innovative process, less amount of residue can be used to replace fossil
K. Hanaki and J. Portugal-Pereira