Page 79 - Materials Chemistry, Second Edition

LIFE CYCLE INVENTORY MODELING IN PRACTICE 61

of the scrap, because the coated scrap must be repulped and the fiber separated
from the coatings before the fiber can be used to make a useful product.
When deciding whether it is appropriate to apply credits for using postin-
dustrial scrap, one should consider the current utilization of this type of scrap.
If the scrap is currently being fully utilized (e.g., kraft clippings from box
manufacture), use of the scrap diverts the material from some other use rather
than diverting it from disposal. Material production burdens can be allocated
between the primary product and the scrap based on the mass of input mate-
rial that ends up in the finished product and the mass of scrap that leaves the
system boundaries as input to another product.
However, if the scrap requires additional reprocessing, as in the example of
coated cartonboard scrap, then the scrap material will be used only if the extra
reprocessing steps can be economically justified. In this situation, virgin mate-
rial burdens may be allocated between the primary product and the converting
scrap based on the relative quantities of material that end up in the primary
product and in the converting scrap, and the relative economic value of the
virgin material and the devalued scrap.

3.4.5 Water Use

In recent years water use, in particular freshwater use, has become an area
of increased interest in life cycle inventories and assessments [7]. However, a
large body of life cycle data has been developed over the years without gath-
ering accompanying water use data, making it necessary to add water use to
data sets where it is missing.
It is interesting to note that a similar situation existed when global warm-
ing became recognized as an important environmental issue. Prior to that
time, carbon dioxide emissions had not been tracked in LCI databases because
there had been no environmental reporting requirements for carbon dioxide.
Adding carbon dioxide emissions to LCI databases was relatively easy, how-
ever, since carbon dioxide emissions can be estimated based on the carbon con-
tent of material. Water use, on the other hand, is more difficult to characterize
and quantify, since there are many forms of water use and different types and
sources of water that can be utilized.
Water use is a broad term that can include any form of use that makes water
permanently or temporarily unavailable for use by another system. Water use
can be generally classified as in-stream use or off-stream use [7]. Off-stream
use involves withdrawal from a water source, while in-stream uses do not.
Examples of in-stream use are hydroelectric generation, water transport, fish-
eries, or recreational uses such as boating.
Off-stream uses involving water withdrawals can be further classified as
degradative or consumptive. Degradative use returns the water to the same
watershed from which it was withdrawn, but with changes in quality (e.g.,
addition of contaminants, temperature changes). Consumptive use refers to
water that is withdrawn from one source and returned to a different water
body or watershed (e.g., depleting the initial water source but adding to the