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Reusable vs. disposable cups revisited: Guidance in life cycle comparisons addressing scenario, model, and parameter uncertainties for the US consumer

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Purpose Despite interest in an environmentally conscious decision between disposable and reusable cups, a comprehensive and current study for US consumers is not yet available. Guidance in favor of single-use cups rely on outdated or non-ISO-compliant results with limited uncertainty information. Such claims are insufficiently generalizable. This article delivers an updated comparative life cycle impact assessment of reusable ceramic cups and single-use expanded polystyrene cups. Methods The ReCiPe midpoint model was selected. Scenario uncertainties are addressed by evaluating compliant standard dishwashing appliance models from 2004 to 2013 used in 26 US subregional utility grids. A utility snapshot from 2009 is applied with extension to recent shifts in generation from increased penetration of natural gas and renewable energy. Parameter uncertainty is quantified through statistical methods. Results Where there is statistical difference, results almost entirely favor reusable cups in the USA. For climate change, 16 % of users have higher impact for ceramic cups washed in 2013 by minimally compliant dishwashers. Higher climate change impacts for 32 % of reusable cup users is indicated with 2004 average dishwashers, though using a cup twice between washes shifts the impact in favor of the reusable cup. Conclusions Disposable cup scenarios do not account for film sleeves, lids, printing, and less conservative shipping weights and distances and therefore reflect a best case scenario. Impact for reusable cups is expected to decrease further as the electricity mix becomes less CO2-intensive with replacement of coal-fired generators by natural gas, wind, and solar and as less efficient dishwashers are replaced with new units compliant to current laws.
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Int J Life Cycle Assess (2014) 19:931–940
DOI 10.1007/s11367-013-0697-7
PACKAGING SYSTEMS INCLUDING RECYCLING
Reusable vs. disposable cups revisited: guidance in life cycle
comparisons addressing scenario, model, and parameter
uncertainties for the US consumer
Laura Woods ·Bhavik R. Bakshi
Received: 8 May 2013 / Accepted: 31 December 2013 / Published online: 25 February 2014
© Springer-Verlag Berlin Heidelberg 2014
Abstract
Purpose Despite interest in an environmentally conscious
decision between disposable and reusable cups, a compre-
hensive and current study for US consumers is not yet
available. Guidance in favor of single-use cups rely on out-
dated or non-ISO-compliant results with limited uncertainty
information. Such claims are insufficiently generalizable.
This article delivers an updated comparative life cycle
impact assessment of reusable ceramic cups and single-use
expanded polystyrene cups.
Methods The ReCiPe midpoint model was selected.
Scenario uncertainties are addressed by evaluating compli-
ant standard dishwashing appliance models from 2004 to
2013 used in 26 US subregional utility grids. A utility snap-
shot from 2009 is applied with extension to recent shifts
in generation from increased penetration of natural gas
and renewable energy. Parameter uncertainty is quantified
through statistical methods.
Results Where there is statistical difference, results almost
entirely favor reusable cups in the USA. For climate change,
16 % of users have higher impact for ceramic cups washed
in 2013 by minimally compliant dishwashers. Higher cli-
mate change impacts for 32 % of reusable cup users is
indicated with 2004 average dishwashers, though using a
cup twice between washes shifts the impact in favor of the
reusable cup.
Responsible editor: Hans-J¨urgen Garvens
L. Woods ·B. R. Bakshi ()
William G. Lowrie Department of Chemical and
Biomolecular Engineering, The Ohio State University,
Columbus, OH 43210, USA
e-mail: bakshi.2@osu.edu
Conclusions Disposable cup scenarios do not account for
film sleeves, lids, printing, and less conservative shipping
weights and distances and therefore reflect a best case
scenario. Impact for reusable cups is expected to decrease
further as the electricity mix becomes less CO2-intensive
with replacement of coal-fired generators by natural gas,
wind, and solar and as less efficient dishwashers are
replaced with new units compliant to current laws.
Keywords Sustainability ·Uncertainty ·Consumer
choice ·Midpoint impact assessment
1 Introduction
In 2010, the USA accounted for 37 % of food service dis-
posables globally and is projected to remain the largest
market for these consumable goods by a wide margin
(Freedonia Group Inc. 2011). Over 500 billion dispos-
able cups are sent to landfills every year (Forsyth 2012).
Despite the strong interest in assessing the life cycle foot-
print of reusable and disposable cups, previous studies have
been too narrow in scope for making generalizable claims
(Hocking 1994; Ligthart and Ansems 2007). One of the
largest shortcomings of the most cited works by Hocking
in 1994 and the Nederlandse Organisatie voor Toegepast
Natuurwetenschappelijk Onderzoek (TNO) in 2007 is the
assumption of cup size, which were evaluated at 8 oz or less
when the actual average portion size in the USA is around
16 oz (Hocking 1994; Ligthart and Ansems 2007; Nielsen
and Popkin 2003). Furthermore, these previous works lack
resolution in the feedstock for power generation by assum-
ing a national average and are outdated regarding recent
power generation trends. Hocking’s work addressed only
cumulative energy demand. TNO’s publication used CML
932 Int J Life Cycle Assess (2014) 19:931–940
2002 and a shadow price approach. Aside from high con-
tribution of ecotoxicity to conclusions in the TNO study
and guidance in cautious use of ecotoxicity for policy and
decision making (Aboussouan et al. 2004), the conclu-
sions cited by the TNO study further suffer from parameter
uncertainty that is not addressed in the report’s sensitivity
analyses. Nonetheless, these studies have been cited exten-
sively as guidance for consumer purchasing and business
operations. A more thorough literature review is available in
the Supporting Information.
Analysis in this updated study covers both polyethylene-
coated paper (PE-paper) cups and expanded polystyrene
foam (EPS) cups for single-use systems with glass, ceramic,
and varying plastic blends for the reusable system. Since
past research has produced inventories and analyses for EPS
versus PE-paper (Franklin Associates Ltd. 2006), iterations
of this study lead to a focus on EPS and ceramic cups in
parsing results.
Ceramic cups were chosen both for consistency with pre-
vious studies and because they tend to have higher impacts
than similar reusable plastic cups designed for equivalent
life span. Of the reusable cups considered, none are specif-
ically advocated as the most preferred in the scope of
this study. Nonetheless, clarity is required in differentiat-
ing reusable cups that are used-as-designed for hundreds
or thousands of uses and those that fail to maintain emo-
tional durability as defined by Chapman (Chapman 2009)
such that they are not utilized fully for a designed life span
through loss, breakage, or disfavor. Such matters, though a
critical part of research in sustainable consumption,are out-
side of the scope of this study, which takes the view that 500
uses of a reusable cup conservatively describes true usage.
To assume less would bring in social and moral issues in
consumption, which cannot be captured by traditional LCA,
but are a necessary field of research as part of a toolbox
for sustainability. Regarding an adequate and appropriate
steady-state approximation, iterations of the analysis found
this figure to be well beyond the point at which the use
phase dominates the impact entirely for ceramic, glass, and
durable plastic cups. Still, results regarding break-even uses
for climate change are provided in Supporting Information.
This article contributes to the literature by analyzing an
essential consumer item: a drinking cup, where the average
US consumer may be presented with the choice between cup
types multiple times per day. This study frames the choice
realistically according to realized trends in consumer appli-
ance ownership and average portion size. Washing energy
is evaluated according to subregional electrical utility mixes
instead of a national average. With scenario and model
uncertainty addressed in framing the problem, parameter
uncertainty is addressed in interpretation of results. The
approach taken overcomes shortcomings of previously pub-
lished findings.
Key findings of the study are the superiority of reusable
cups in climate change impact in most regions of the USA
with only approximately 32 % of the residential popula-
tion having a higher climate change impact for the oldest
appliance technology assessed. This figure drops to about
16 % for US consumers using a minimally compliant 2013
dishwasher model. This study also finds even for regions
with highest climate change impact, reusable cups have
comparable or lower impacts in nearly every other indicator
of the ReCiPe method. Contrary to prior reports, rinsing
a cup and using only twice between washes is sufficient
for improving climate change impacts for consumers with
dated dishwashers in regions of higher impact. These results
indicate a strong life cycle environmental benefit of using
reusable cups.
This article begins by laying out assumptions of the
model and scenarios evaluated. Then, a comparison to
energy analyses of previous studies is provided. From here,
a case is made for conducting a midpoint impact assess-
ment according to regional utility mixes rather than national
averages using the ReCiPe method. Results of the midpoint
assessment are presented using statistical methods for com-
paring the means of two independent lognormal distribu-
tions to determine statistical significance in comparison of
results. This is followed by a discussion of results and impli-
cations of changing electrical utility mixes and differenti-
ation between residential and industrial purchasing behav-
iors. The Supporting Information includes a more detailed
literature review and background; a comparison to the 2007
TNO study; more information on modeling assumptions,
tools, statistical methods, and grid details; additional uncer-
tainty and midpoint graphs; and an extension of results to
a regional mix undergoing changes due to increased natural
gas and renewable energy penetration in 2012.
1.1 Assumptions and problem design
Many methods and inventory practices have been developed
and aided through standardization since the mid-1990s.This
study applies process modeling using SimaPro 7.2.4 with
Ecoinvent v2 database and a selection of impact methods
available in the software. In the analysis, cumulative energy
demand (CED), CML 2, TRACI2, and ReCiPe midpoint
methods were applied to gain insight on past studies and
conflicting results. The ReCiPe midpoint method has been
selected for reporting final conclusions based on its more
recent development, which has addressed some of the issues
in ecotoxicology assessment raised in the CML model.
More information on various life cycle impact assessment
(LCIA) methods and software can be found in the litera-
ture and in the Supporting Information (EarthShift 2011;
Ecoinvent Centre 2007; Althaus et al. 2010; Joint Research
Commission (JRC) 2010).
Int J Life Cycle Assess (2014) 19:931–940 933
The life cycle diagram in Fig. 1shows activities that form
the analytical space, showing only the EPS and reusable
models. Ecological flows (emissions, effluents, raw mate-
rial acquisition, etc.) are implicit to the diagram, from which
the inventory is constructed. The following sections discuss
the features of the process network.
1.1.1 Cup manufacture and end-of-life
The cup size is 16 oz (473 mL), keeping with current trends
and analyses (Franklin Associates Ltd. 2006; Franklin
Associates 2011; Nielsen and Popkin 2003). More discus-
sion on cup size is in the Supporting Information.Themass
of the disposable cups from the Franklin study in 2006
is used here, which is 4.4 to 5.0 g/cup for EPS (Franklin
Associates Ltd. 2006). For the reusable cups, impact has low
sensitivity to cup mass within its useful life; a range was
applied capturing low- to high-weight retail samples. For
ceramic cups, this range was 292 to 700 g/cup.
For both paper and plastic single-use serviceware, recy-
cling is negligible in the US municipal solid waste system
(US Environmental Protection Agency (EPA) 2009). In
both cases, the US average for solid waste incineration,
11.7 %, is assumed (US Environmental Protection Agency
(EPA) 2011). Incineration for energy recovery is consid-
ered avoided production. The remaining is assumed to be
landfilled. Sensitivity analysis provides sufficient insight for
variations in waste handling across regions. There are 86
waste incineration facilities in 24 states by 2010 figures,
where the incineration rate would be higher than the cited
average (Michaels 2010). Highest throughput facilities are
distributed primarily in the northeast, Florida in the south,
and Pennsylvania in the midwest. Remaining regions have
little to no substantial municipal waste-to-energy activities,
so the reality in these areas would approach 100 % landfill
for cups disposed in trash receptacles.
Ceramic is not considered recyclable, while less than
15 % of glass containers are recycled annually(US Environ-
mental Protection Agency (EPA) 2009). Both are designated
as 100 % landfill.
Corrugated cardboard has a 76.6 % waste stream recov-
ery rate, which is modeled in the disposable cup system
(US Environmental Protection Agency (EPA) 2011). It is
assumed as a first approximation that 76.6 % of the card-
board packaging is diverted from landfill or incineration
with 50 % of diverted materials resulting in avoided produc-
tion or reuse.
A conservative value was placed evenly on the disposable
cups for transportation and packaging. The average dis-
tance for delivery of materials and products by diesel truck
was set at 200 miles. Packaging for transportation of the
raw materials was neglected. Only corrugated cardboard for
distribution of the final product at 1,000 units per box. Pack-
aging film sleeves, cup lids, and individual cup sleeves were
not included in the inventory. The corrugated cardboard is
assumed to add 10 and 20 % to the final shipped product
mass for paper and polystyrene cups, respectively. These
figures were estimated based on an evaluation of average
cup mass and shipping weights and roundeddownward. The
sum total of these assumptions leads to results that represent
a lower limit of impact for the single-use system.
incinerate (11.7%) landfill (88.3%)
cardboard recovery use
packaging and transportation
forming
transportation
expandable polystyrene manufacture
(a) expanded polystyrene
wastewater treatment
landfill
detergent manufacture
tap water
dishwasher
use
distribution
transmission
electricity generation
use
reusable cup manufacturing
(b) reusable: glass, ceramic, or plastic
Fig. 1 Technical system life cycle diagram each type of cup
934 Int J Life Cycle Assess (2014) 19:931–940
1.1.2 Use phase
Fifty to seventy-five percent of American homes are
equipped with a dishwashing appliance (Hoak et al. 2008;
Emmeletal.2003; California Energy Commission (CEC)
2010; Boustani et al. 2010). Thus, from the US con-
sumer perspective, it is assumed, on average, that signifi-
cant domestic population have access to a dishwasher with
relative ease and frequency. Results of this study are trans-
ferable to the workplace in the event that a standard-sized
dishwasher is provided for employee use within the range
of assumptions.
Energy, Water, and Detergent The E-SCOPE study con-
ducted in the UK to inform appliance take-back policies in
the mid to late 1990s found that the average age of discarded
dishwashers was 9 years (Cooper and Mayers 2000; Cooper
2005). While a Department of Energy analysis yielded a
mean age of 15 years based on a Weibull distribution for
likelihood of failure (US Department of Energy Office of
Energy Efficiency and Renewable Energy (OEERE) 2012;
U.S. Department of Energy (DOE) 2012), this study will
assume values based on the direct observations of consumer
behavior from E-SCOPE. Table 1lays out values for energy
and water use of dishwashers dating back to average pur-
chases in 2004. For current models, energy and water use
are cited from Federal Register and Energy Star require-
ments for compliance and certification (U.S. Government
Printing Office (USGPO) 2012; U.S. Environmental Protec-
tion Agency (EPA) 2013a;2013b). Energy use is reported
in kilowatt hour per year, including energy use per cycle
plus standby power, assuming 215 cycles/year. The energy
factors (EF, cycle per kilowatt hour) in Table 1are derived
accordingly.
For earlier years, energy factors represent average con-
sumer purchases, as determined in a report tracking appli-
ance market shares in California prior to incentivization
measures (Pulliam 2009). Average EF for dishwashers
increased from 0.52 in 1999 to 0.66 in 2007. With the
passage of the “Energy Independence and Security Act”
of 2007, water efficiency became explicitly part of DOE
dishwasher efficiency standards. Energy use in dishwash-
ers is most highly correlated to water use for heating (Hoak
et al. 2008). Therefore, for the average purchased dish-
wasters in 2004 and 2007, water consumption is assumed
from the corresponding EF from guidelines. Units having
EF of 0.6 and 0.66 correspond to maximum water use of
6.5 and 5.8 gal/cycle, respectively, according to Depart-
ment of Energy requirements for compliance and energy star
ratings (U.S. Government Printing Office (USGPO) 2012;
U.S. Environmental Protection Agency (EPA) 2008).
Detergent mass follows from a review of dishwasher
operation manuals and consumer tips on labels of
powder detergents. A review of material safety and data
sheets for detergents and self-reported product ingredient
listings showed sodium carbonate (Na2CO3) is common and
appreciable in concentration. In productionof laundry deter-
gents, raw material supply was dominant over total product
manufacture, including packaging (Saouter and van Hoff
2002). In order to keep the scope manageable, production
of 100 % Na2CO3is assumed as a proxy. Sodium sul-
fate, sodium chloride, and layered sodium silicate were also
included in analysis iterations, but the impact of different
formulations was found negligible compared to influences
from energy use of the washing unit.
User behavior To fairly allocate the fraction of impact
in washing attributed to a single cup, assumptions must
be made regarding capacity loading. Dishwashers are
designed with a larger volume designated to the bottom rack
leaving the top rack to occupy about 40 % of the wash
volume. This allows the bottom rack to be reserved for large,
unusually shaped items as dinner plates, pots, and pans
while the top rack is designed primarily for cups and other
small items. Reasoning that 25–30 cups can fit in the upper
rack, a conservative assumption is made such that a single
cup is allocated a fraction of 1
60 of the dishwasher capacity,
assuming a fully loaded unit. A consumer study found that
93 % of study participants report running their dishwash-
ing appliance only when full (Emmel et al. 2003). Drying
cycles are assumed corresponding to compliance testing
procedures.
Table 1 Dishwasher energy
and water use 2004–2013 Energy factor Water use
Year Rating cycle/kWh L/cycle (US gal/cycle)
2004 Average purchase (AP) 0.59 24.6 (6.5)
2007 Average purchase (AP) 0.66 22.0 (5.8)
2013 Minimally compliant (MC) 0.70 18.9 (5.0)
2013 Energy star (ES) 0.73 16.1 (4.25)
2013 Best available technology (BAT) 1.19 8.3 (2.2)
Int J Life Cycle Assess (2014) 19:931–940 935
2 Methods
Beginning with an energy analysis, methods of approach
were in keeping with trends dating back to the work of
Hocking (Hocking 1994). Then, midpoint analysis with
attention to uncertainty are presented for a set of reasonably
generalizable conclusions for the US consumer. A case is
made for disaggregation according to regional utilities, for
evaluating this comparison with more recently developed
LCIA methods, and for greater attention to be placed on
uncertainty for fair reporting. The functional unit for anal-
ysis and reporting is impact per use of each cup. The basis
of the assumption is one wash or disposal for each use,
respectively. Some details have been described underlying
the assumptions in this respect, e.g., model energy factor,
uses per cup life, and cup mass. More details are in the
Supporting Information.
2.1 Energy analysis
The values for energy demand reported by Hocking (1994),
Denison (1998), and Franklin Associates Ltd. (2006)are
superimposed to this study’s energy analysis results in
Fig. 2. An extrapolation to Hocking’s figures is made for
16-oz cups. In this graph, line spread captures mean val-
ues for scenario ranges described above. For disposable
cups, variability in cup mass is reflected. For reusable cups,
variability in energy and operational efficiencies are cap-
tured. Variations include range of cup mass, energy factors,
water and detergent use, and capacity loading. Figure 2
takes the approach used by the references cited, combin-
ing various energy fuel sources for a cumulative figure,
though it is recommended in current practice to report the
fuel sources individually. These details are in the Supporting
Information.
0
100
200
300
400
500
600
700
800
900
8 oz 16 oz 8 oz 16 oz
PE-paper EPS ceramic glass
Combined CED, kJeq/use
’94
’94ext
’94
’94ext
’94Can ’94Can
’94U.S.’94U.S.
’98 ’98
’98
’06
’06
Fig. 2 Comparison of combined cumulative energy demand, notated
by year of publication (Hocking 1994;Denison1998; Franklin Asso-
ciates Ltd. 2006). ext, extrapolation to 16 oz; Can/U.S, Canadian and
US average electricity generation scenarios
There is agreement in this study’s results and previous
studies where assumptions have been aligned. While dish-
washer use dominates the impacts of reusable cups over the
useful life, impact is not similarly affected by size as larger
cups occupy about the same amount of space in the unit.
The Franklin Associates study is assumed the most com-
prehensive and relevant study on disposable serviceware
(Franklin Associates Ltd. 2006). Where our figures come
in somewhat lower, they are in good agreement and par-
ticularly conservative with respect to the Franklin study.
Packaging assumptions in this study are more conservative
than those in the Franklin study, which would have a larger
impact on the polystyrene cups than the paper cups. The
Franklin study assumed packaging of 500 units per box,
adding corrugated cardboard in the amount 68 and 17 % of
the cups’ mass for EPS and PE-paper cups, respectively. The
figure reported from the Franklin study in Fig. 2includes
packaging and waste-to-energy credits applied in the study
for fair alignment of boundaries.
The largest influence on cumulative energy demand
across the reusable cups is dishwasher power requirements,
which correlates to utility grid assumption, percent of
washer capacity loading, and energy efficiency of the unit.
Previous studies assume an average national electricity mix
and are neither current nor geographically relevant across
the USA. Figure 3expands the utility grid assumption into
26 US regions, in approximate descending order of popu-
lation, as reported in the EPA’s Emissions and Generation
Resource Integrated Database (eGRID) (U.S. Environmen-
tal Protection Agency (EPA) 2012). The population order-
ing in this case is to avoid arbitrary data visualization. It
is acknowledged that there is a significant cross-regional
transmission. This is addressed further in context of uncer-
tainty in the midpoint results and in the discussion section.
Subregion names and a breakdown of utility grid mixes for
each region is provided in the Supporting Information.
2.2 Midpoint assessment and uncertainty analysis
While comparison with previous studies, including the TNO
study (discussed further in the Supporting Information)
gives us some information, especially regarding impact cor-
relations to size in disposable cups, the level of resolution
is not high enough to accurately demonstrate sensitivity on
energy use and other factors for this study. First, model
and scenario uncertainties were addressed by disaggrega-
tion across subregional utilities, modeled with 2009 data,
and accounting for representative dishwasher models span-
ning older models still in operation to 2013 purchases.
936 Int J Life Cycle Assess (2014) 19:931–940
Fig. 3 Combined cumulative
energy demand per use of 16-oz
cup across regions of US
electricity grid
0
100
200
300
400
500
600
700
800
900
PE-paper
EPS
CAMX
RFCE
ERCT
SRVC
RFCW
NWPP
SRMW
FRCC
NYUP
SRSO
NEWE
MROW
SRTV
SRMV
RFCM
AZNM
MROE
RMPA
SPNO
SPSO
NYLI
NYCW
HIOA
AKGD
HIMS
AKMS
Combined cumulative energy demand, kJ-eq/use
An inventory analysis revealed positive skewness with char-
acteristic mean >median >mode. Nearly all distributions
in Ecoinvent v2 unit processes are designated lognormal.
Much of the Ecoinvent v2 data has uncertainty informa-
tion associated with inventory items, which is determined
through combinations of measurements, estimates, and a
pedigree matrix approach described in literature (Weidema
1998;Ecoinvent2007). Over 70 % of the inventory for this
study contained uncertainty information through these semi-
quantitative methods. For comparison in any impact cate-
gory, an investigation of the measures of central tendency is
warranted.
2.2.1 Measures of central tendency
Use of SimaPro’s “analyze” and “compare” functions gen-
erates mean value output. This is what is generally reported
in LCA literature where this software is used for processing
inventories. For example, Fig. 4shows two sets of results for
climate change (CC). Figure 4a shows mean output across
the range of scenarios, similar to the range shown in Fig. 3,
demonstrating utility mix effects. For the single-use cups,
variation corresponds to cup mass. For the reusable cups,
across the subregions, the range includes user and appli-
ance efficiencies. Figure 4b gives box plots resulting from
parameter uncertainty for one scenario, or one combina-
tion of sensitivities relating to mass, energy use, etc. The
mean value in the box plot, designated by a sideways hash
mark, corresponds to the output in Fig. 4a designated with
the darkened circle. For other points along the range in
Fig. 4a, parameter uncertainty graphs would show a shift in
the mean and a corresponding shift in confidence intervals.
Inventory components contributing most to CC in this
study have smaller standard deviations designated in the
inventory than those having highest contributions to other
impacts such as ionizing radiation, human toxicity, and
ecotoxicity. Figure 4is an example where the mean is a rea-
sonable measure of central tendency for comparison of the
EPS and reusable cups, and there is greater variation in sce-
nario uncertainty than parameter. On the other hand, where
the largest contributors to ionizing radiation (IR) in the
inventory have higher uncertainty designation, the spread is
much greater, as shown in Fig. 5, such that the compari-
son of mean values may not accurately reflect differences in
impact. Figure 5is an example where parameter uncertainty
has greater influence than scenario. Higher uncertainty may
be attributed to a number of factors, including more com-
plex geochemical influences on substances in the ground
and water compartments; inventory data quality regarding
time, location, and technology; or variation in reporting
requirements across industries and regions.
It is known that mean and standard deviation are highly
sensitive to extreme points, and it is often recommended
by statisticians to use the population median rather than the
mean as a measure of central tendency when dealing with
a skewed distribution (Singh et al. 1997). For both Figs. 4b
and 5b, the whiskers reflect the median plus 1.5 times the
interquartile ratio.
Given the output from SimaPro and basic knowledge
on the distributions for each indicator in each region in
the neighborhood of analysis, an approach was constructed
from the Cox method for estimating confidence intervals
and the Z-score method for comparing the means of two
independent lognormal distributions (Olsson 2005; Zhou
et al. 1997).
2.2.2 Estimation of parameters
For approximately lognormal distributions, where ln X
Nμn2
n, hypothesis testing developed by Zhou et al.
(1997) can be applied for comparing samples with unequal
variances as follows:
Z=
ˆμn,2−ˆμn,1+(1/2)(S2
n,2S2
n,1)
S2
n,1
n1+S2
n,2
n2+(1/2)S4
n,1
n11+S4
n,2
n21
(1)
where ˆμnand S2
nare maximum likelihood estimators of
the sample mean and unbiased estimators of the sample
variance, respectively.
Int J Life Cycle Assess (2014) 19:931–940 937
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
PE-paper
EPS
CAMX
RFCE
ERCT
SRVC
RFCW
NWPP
SRMW
FRCC
NYUP
SRSO
NEWE
MROW
SRTV
SRMV
RFCM
AZNM
MROE
RMPA
SPNO
SPSO
NYLI
NYCW
HIOA
AKGD
HIMS
AKMS
Climate change: kg CO2 eq
(a) Sensitivity analysis (scenario and model uncertainty)
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
PE-paper
EPS
Usavg
CAMX
RFCE
ERCT
SRVC
RFCW
NWPP
SRMW
FRCC
NYUP
SRSO
NEWE
MROW
SRTV
SRMV
RFCM
AZNM
MROE
RMPA
SPNO
SPSO
NYLI
NYCW
HIOA
AKGD
HIMS
AKMS
Climate change: kg CO2 eq
(b) Parameter uncertainty (Usavg = U.S. average)
Fig. 4 Climate change (CC); kilogram of CO2-eq per use: The scenario marked by a circle in (a) is one of a range of scenarios and corresponds
to parameter uncertainty analysis in (b)
To perform the comparison, the Cox method for esti-
mating confidence intervals is used to estimate S2
nand ˆμn
with knowledge on the upper and lower bound of the inter-
vals at 95 % confidence. The full equations are given in the
Supporting Information.
3 Results and discussion
Following this approach, tables were constructed for com-
paring sample means, μs,EPS and μs,reuse, for each region
and scenario by the Z-score test. For example, inventory
uncertainty for substances characterized for radiative forc-
ing, or climate change, is relatively low. In this case, visual
inspection of Fig. 6would lead closely to the Z-score
results, where a green circle indicates the reusable cup has
a lower impact than the EPS cup for the relative US region
and appliance efficiency. A red diamond indicates a lower
impact for EPS, while a yellow triangle indicates no signifi-
cant difference. One way to consider these results is to note
that, of the top ten most populous US cities, only one city
(Chicago, IL) is located in a subregion (RFCW) with higher
climate change impact for the 2004 units. The othernine are
in the regions CAMX, AZNM, SRMV, ERCT, RFCE, and
the New York cluster. Climate change is influenced by util-
ity mix and is correlated with cumulative energy demand
only insofar as the utility is CO2-intensive.
There is significant transmission across colocated subre-
gions, so Fig. 6is organized by subregional utility groups,
shown as boxed groups in the icon chart in approximately
decreasing order of regional population. Where the distri-
bution of Zin Eq. 1is approximately standard normal,
significance was set as exceeding a score of ±1.96 for 95 %
confidence. Graphs and Z-score icon tables demonstrate
model uncertainty in terms of region and energy efficiency
of the appliance coupled with the parameter uncertainty
communicated by the error bars. Figure 6shows the nine
subregions with the highest percentage of coal for electric-
ity generation have the highest scores for climate change.
This is according to the 2009 figures. After presenting the
results, the discussion will address how the changing util-
ity mix and other considerations would impact conclusions
further.
Similar to ionizing radiation having higher variance,
results for particulate matter (PM) formation, shown in
Fig. 7, are skewed with greater spread making comparison
of means less straightforward. For almost all regions, the
best available technology has significantly lower impact for
reusable cups. For units as efficient as the 2004 model aver-
age purchase, there is not a significant difference between
0
0.005
0.01
0.015
0.02
0.025
Ionising radiation: kg U235 eq
(a) Sensitivity analysis (scenario and model uncertainty)
0
0.005
0.01
0.015
0.02
0.025
PE-paper
EPS
CAMX
RFCE
ERCT
SRVC
RFCW
NWPP
SRMW
FRCC
NYUP
SRSO
NEWE
MROW
SRTV
SRMV
RFCM
AZNM
MROE
RMPA
SPNO
SPSO
NYLI
NYCW
HIOA
AKGD
HIMS
AKMS
PE-paper
EPS
Usavg
CAMX
RFCE
ERCT
SRVC
RFCW
NWPP
SRMW
FRCC
NYUP
SRSO
NEWE
MROW
SRTV
SRMV
RFCM
AZNM
MROE
RMPA
SPNO
SPSO
NYLI
NYCW
HIOA
AKGD
HIMS
AKMS
Ionising radiation: kg U235 eq
(b) Parameter uncertainty (Usavg = U.S. average)
Fig. 5 Ionizing radiation (IR); kilogram of U235-eq per use: The scenario marked by a circle in (a) is one of a range of scenarios and corresponds
to parameter uncertainty analysis in (b)
938 Int J Life Cycle Assess (2014) 19:931–940
0
0.01
0.02
0.03
0.04
0.05
SRMW
SRMV
SRSO
SRTV
SRVC
CAMX
NWPP
RMPA
AZNM
RFCE
RFCM
RFCW
NYLI
NEWE
NYCW
NYUP
ERCT
FRCC
MROE
MROW
SPNO
SPSO
HIOA
HIMS
AKGD
AKMS
EPS
Climate change: kg CO2 eq
Fig. 6 Results across five models (described in Table 1) for climate change (kilogram of CO2-eq per use): mean of EPS (μEPS ) is compared to
each regional mean for ceramic mugs (μreuse,region)byZ-score comparision of two independent lognormal distributions
the two cup types, except in the subregion RFCM, which is
roughly the Michigan lower peninsula.
Remaining ReCiPe midpoint results are available in
the Supporting Information. All impacts except land use
and water depletion categories were correlated entirely to
energy use in the dishwasher. For all of these categories,
except ozone depletion (OD) and climate change, results
are either not significantly different or else favor reusable
cups. For ozone depletion, impact is mostly correlated to
nuclear power generation. Only SRVC and RFCE, which
have the highest percentage of nuclear power, have higher
impact for best available technology in this category. There
are some CFC emissions associated with uranium enrich-
ment in the inventory. In contrast, most regions with higher
ozone depletion values score significantly lower for climate
change.
Land use was considered outside of the scope of this
comparison. Water depletion and metal depletion showed
higher impact for reusable cups. While water depletion for
EPS is embodied water, that for reusables is throughput,
which is not consumed. The reason being that water deple-
tion was calculated in the method almost entirely from the
draw of tap water for washing. Only a small percentage
of the results were due to evaporative losses or embodied
0
0.00002
0.00004
0.00006
0.00008
0.0001
0.00012
Particulate matter formation: kg PM10 eq
SRMW
SRMV
SRSO
SRTV
SRVC
CAMX
NWPP
RMPA
AZNM
RFCE
RFCM
RFCW
NYLI
NEWE
NYCW
NYUP
ERCT
FRCC
MROE
MROW
SPNO
SPSO
HIOA
HIMS
AKGD
AKMS
EPS
Fig. 7 Results across five models (described in Table 1) for climate change (kilogram of PM10-eq per use): mean of EPS (μEPS) is compared to
each regional mean for ceramic mugs (μreuse,region)byZ-score comparision of two independent lognormal distributions
Int J Life Cycle Assess (2014) 19:931–940 939
water, leaving the results to be interpreted as throughput not
depletion of water. It is debated how water may be incor-
porated into LCA studies by impact rather than throughput;
Ecoinvent reports water use, not consumption (Berger and
Finkbeiner 2012).
Similarly, metal depletion results are based on the
amount of copper used in transmission and distribution. The
copper is considered depleted by reference of having been
extracted from the Earth, but forming into electrical cables
is not a dissipative activity such as incorporation of cop-
per to circuit boards or consumer electronics, leaving this
category open to interpretation, since the method would
consider copper for either aggregate or dissipative activities
equivalently.
Reusable cups meet at least two of three strategies laid
out for maintaining quality of life with lower rates of new
product purchasing: life extension, shared ownership, and
product repair (Allwood et al. 2011). Results presented
show that, for many regions across the USA, reusable cups
are a better choice than polystyrene cups for typical serv-
ing sizes when washed in a standard-sized dishwasher once
for every use. It is reasonable to assume that an individ-
ual using a reusable cup is more likely to rinse and reuse
a cup throughout the day if it is a personal item than if
it is a single-use item. Performing the same procedure for
the SRMW subregion assuming an average of two uses
per wash resulted in improvements in all indicators. For
the 2004 average purchased model in climate change and
particulate matter formation, the impact is less than the
single-use polystyrene disposable and is lower than one use
per wash with the best available technology. Ozone deple-
tion impact was lowered from worse to not significantly
different. Details are in the Supporting Information.
According to the Energy Information Administration’s
Electric Power Annual for 2011, green pricing has been
entirely driven by the residential sector, where 92.9 % of
green pricing customers are residential, 7 % commercial,
and 0.1 % industrial (U.S. Energy Information Adminis-
tration (EIA) 2013). This implies that credit for cleaner
portion of utility mixes goes to the residential consumer for
electricity use in the home.
The impact of a changing utility mix with higher penetra-
tion of renewable technologies and the increased domestic
availability of natural gas also leads to additional con-
clusions. Net capacity additions for natural gas-fired and
renewable generators continue to increase with 56.8-GW
net summer capacity additions in natural gas, wind, and
solar predicted for 2012–2016 (U.S. Energy Information
Administration (EIA) 2013). For the same period, net
summer capacity for coal-fired generators is expected to
decrease by 4.1 GW. The current condition for SRMW was
investigated to compare the impact from the 2009 eGrid
mix to 2012 figures reported by the US Energy Informa-
tion Administration (U.S. Energy Information Administra-
tion (EIA) 2012). Applying the same analytical approach,
improvements were seen in all impacts. Details are in the
Supporting Information.
One final item of consideration in interpreting the results
is interstate electricity imports. Electricity import and export
of colocated regions is a function of the population and busi-
ness distributions. Nonetheless, interstate transmission is
assumed to impact comparative results minimally. Accord-
ing to analysis by Marriott and Matthews (Marriott and
Matthews 2005), outside of California, most of interstate
transmission occurs between states that are already assessed
as regional groups. For example, WV exports to VA and
MD, both of which partially belong to RFCE as does WV.
Similarly, while CA imports a significant amount, it is
generally coming from other WECC regional states, not
including RMPA.
Finally, while a demonstrative study, it has been implied
by Lave et al. that disposable cups may have higher indi-
rect impacts through supply chain interactions than those
directly captured in process LCA (Lave et al. 1995). To the
contrary,where the supply chain for electricity production is
less complex than for consumer goods, it is thought that pro-
cess LCA for electricity production in this study effectively
captures most impacts.
Using LCA methodology, the authors intend the frame-
work of this study to be used as guidance for corrective
measures in reporting results of life cycle impact assess-
ments. Unlike the headline “Single-use cups win every
time!” claimed by the Benelux Disposables Foundation
after publication of the TNO report, this study makes no
claim of the ultimate superiority of any cup system (Stitch-
ing Disposables Benelux 2013). It is considered the best
available guidance for US consumer choice in single-use
and reusable cups with respect to regional power mix and
consumer behavior.
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Supplementary resource (1)

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... Plastic materials are known to cause significant damage to the environment and are major contributors to carbon emissions. Although the carbon footprints for plastic and polymers are lower than the alternative materials, the one-time use of plastic materials makes their environmental profile less desirable (Woods & Bakshi, 2014). Undoubtedly, plastic materials have a number of applications and benefits. ...
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