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1.
(From Allen, et al., 1992) At the supermarket checkstand,
customers are asked to choose whether their purchases should be placed
in unbleached paper grocery sacks or in polyethylene grocery sacks. Some consumers make their choice based on the perception of
the relative environmental impacts of these two products. This problem will quantitatively examine life cycle inventory
data on the energy use and air emissions for these two products.
Life
cycle inventories for paper and polyethylene grocery sacks have
resulted in the data given below, and these data will be used in
comparing the two products. Assume that the functional unit to be used in this comparison
is a defined volume of groceries to be transported, and that based on
this functional unit, 2 "1 plastic sacks are equivalent to one
paper sack. Air
emissions and energy requirements for paper and polyethylene grocery
sacks (Allen, et al., 1992)
Note:
These data are based on past practices and may not be current. a.)
Using the data in the Table, determine the amount of energy required
and the quantity of air pollutants released per plastic sack.
Also determine the amount of energy required and the quantity
of air pollutants released for the quantity of paper sacks capable of
carrying the same volume of groceries as the plastic sack.
Both the air emissions and the energy requirements are
functions of the recycle rate, so perform your calculations at three
recycle rates: 0%, 50% and 100% recycled.
Note that a 50% recycle rate indicates that half of the sacks
are disposed of and the other half are recycled after the product use
stage of their life cycle. b.)
Plot the energy requirements calculated in Part a.) as a function of
the recycle rate for both sacks.
Do the same for the air emissions.
Compare the energy requirements and air emissions of the sacks
at different recycle rates. c.)
Discuss the relative environmental impacts of the two products.
Do the results allow for a comprehensive comparison?
d.)
The material and energy requirements of the plastic sacks are
primarily derived from petroleum, a non-renewable resource.
In contrast, the paper sacks rely on petroleum to only a
limited extent and only for generating a small fraction of the
manufacturing and transportation energy requirements.
Compare the amount of petroleum required for the manufacture of
two polyethylene sacks to the amount of energy necessary to provide
10% of the energy required in the manufacture of one paper sack.
Assume 0% recycle and that 1.2 lb of petroleum is required to
manufacture 1 lb of polyethylene.
The higher heating value of petroleum is 20,000 BTU/lb. e.)
In this problem, we have assumed that 2 "1 plastic sacks are
equivalent to one paper sack. Does the uncertainty in the equivalency
between paper and plastic sacks affect any of your conclusions? 2.)
(From Allen, et al., 1992) Disposable diapers, manufactured from paper
and petroleum products, are one of the most convenient diapering
systems available, while cloth diapers are often believed to be the
most environmentally sound. The
evidence is not so clear-cut, however. This problem will quantitatively examine the relative energy
requirements and the rates of waste generation associated with
diapering systems. Three
types of diapering systems are considered in this problem: home
laundered cloth diapers, commercially laundered cloth diapers and
disposable diapers containing a super-absorbent gel.
The results of life cycle inventories for the three systems are
given below. Energy
requirements and waste inventory per 1000 diapers (Allen, et al.,
1992)
a.)
The authors of the report from which the data in the Table are
taken found that an average of 68 cloth diapers were used per week per
baby. Disposable diaper
usage is expected to be less because disposable diapers are changed
less frequently and never require double or triple diapering.
In order to compare the diapering systems, determine the number
of disposable diapers required to match the performance of 68 cloth
diapers, assuming: 15.8
billion disposable diapers are sold annually 3,787,000
babies are born each year children
wear diapers for the first 30 months disposable
diapers are used on 85% of children. Ratio
of impact to home laundered impact
c.)
Using the data given below, determine the percentage of
disposable diapers that would need to be recycled in order to make the
solid waste landfill requirements equal for cloth and disposable
systems. Impact
of recycle rate on solid waste for diapering systems
3.) The University of Michigan has developed a case study analyzing the decision, made by McDonalds, to replace polystyrene clamshell containers with other container systems. The case study is described at: http://www.umich.edu/~nppcpub/resources/compendia/chem.e.html. Review this case study and write a one page summary of the case. |
