Assignments

Assignment 1:

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)

 Life cycle Stages Paper sack air emissions (oz/sack) Plastic sack air emissions (oz/sack) Paper sack air energy req’d (Btu/sack) Paper sack air energy req’d (Btu/sack) Materials manufacture plus product manufacture plus product use 0.0516 0.0146 905 464 Raw materials acquisition plus product disposal 0.0510 0.0045 724 185

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)

 Impact Disposable diapers Commercially laundered cloth diapers Home laundered cloth diapers Energy requirements (million BTU) 3.4 2.1 3.8 Solid waste (cubic feet) 17 2.3 2.3 Atmospheric emissions (lb) 8.3 4.5 9.6 Waterborne wastes (lb) 1.5 5.8 6.1 Water requirements (gal) 1300 3400 2700

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.

b.)  Complete the Table given below.  Remember to use the equivalency factor determined for cloth and disposable diapers determined in part a.).  Based on the assumptions you made in Part a.), how accurate are the entries in the Table?

Ratio of impact to home laundered impact

 Impact Disposable diapers Commercially laundered cloth diapers Home laundered cloth diapers Energy requirements Ratioed to home laundered use 0.50 0.55 1.0 Solid waste Ratioed to home laundered waste 1.0 Atmospheric emissions Ratioed to home laundered emissions 1.0 Waterborne wastes Ratioed to home laundered emissions 1.0 Water requirements Ratioed to home laundered use 1.0

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

 Percentage of diapers recycled Solid waste per 1000 diapers (Cubic feet) 0 17 25 13 50 9.0 75 4.9 100 0.80

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.

Assignment 2:

Streamlined LCA Assignment

Your assignment is to perform a streamlined life cycle assessment of a product of your choice.  You should employ the streamlined LCA methodology outlined in Chapter 13, Section 13.3.  You may also wish to consult Dr. Thomas Graedel's book on Streamlined Life Cycle Assessments (see the references in Chapter 13).

Specifically, organize the life cycle information using the 5-by-5 matrix shown below.

 Material Use Energy Use Solid residues Liquid residues Gas residues Premanufacture 1,1 1,2 1,3 1,4 1,5 Product Manufacture 2,1 2,2 2,3 2,4 2,5 Product delivery 3,1 3,2 3,3 3,4 3,5 Product use 4,1 4,2 4,3 4,4 4,5 Refurbishment, recycle, disposal 5,1 5,2 5,3 5,4 5,5

a.)    For each matrix element assign a score of 0-4, with 4 representing superior environmental performance and 0 representing poor environmental performance.  For each matrix element, write a few sentences justifying your score.  Do this assessment for both the current design of your product and for a previous design.

b.)    Weight the scores for each life cycle stage.  For example, if you were evaluating the life cycle of an automobile, you might weight the use stage more heavily than the production stage, since the bulk of the emissions and energy consumption associated with a vehicle are associated with the use of the vehicle.  Note that the weights, over all life cycle stages, should sum to one.  Also weight the impact categories.  Again, using the example of an automobile, you might weight the gas residue category more heavily than the liquid residue category since the bulk of the emissions over a vehicle’s life are to the atmosphere.  This results in a doubly-weighted matrix.  The details of the weighting approach are described in Dr. Thomas Graedel’s book on Streamlined Life Cycle Assessments (see the references in Chapter 13).  Justify your choice of weighting factors.  Again, a few sentences to a paragraph for each weighting assignment is sufficient.

c.)      Briefly comment on whether this methodology provides insight on the environmental performance of the product you chose.

In performing this assignment, you may wish to consult the EIOLCA web page developed by Carnegie Mellon University.  A description of this web page is given in the Links sections of this web site.