1. Answers are provided from a recent study that addressed a
present hot-button industry issue: Does switching from dual-stream
to single-stream collection and processing of recyclables reduce
greenhouse gas impacts?
By Richard Abramowitz, Michael Timpane and Editorial Staff
T
he growth rate of single-stream collection and processing in the U.S. has
been nearly constant since 1995, at an average of about 14 new facilities per
year. In general, the transition from dual- to single-stream is accompanied
by a significant increase in collected tonnage of recycled materials, and the long-
term effects of the transition depend greatly on numerous characteristics of the
original recycling program, as well as in the community at large. The recyclable
materials yielded in the single-stream approach far outpace the expected increases
in the amount of residue, which were taken into account in the study. Thus, the
increase in recycling is around 50 percent and can vary from only 10 percent, as
was found in the case in Vadnais Heights, Minnesota, to the 100 percent seen by
Springfield, Massachusetts. In fact, in some cases, the high increase in collected
material at the onset of a program can taper off somewhat later on. For example,
Collier County, Florida experienced an initial increase of 77 percent, only to watch
that figure drop to 47 percent over the next few years.
But, do the expanding number of municipal programs making the move to single-
stream collection experience similarly ever-increasing benefits of greenhouse gas (GHG)
emissions reduction? Exactly what GHG benefits are gleaned by making the move to
single-stream collection was the goal of a recent study, Comparison of Greenhouse Gas
Impacts of Dual Stream vs. Single Stream Collection and Processing of Recyclables, prepared
by the Earth Engineering Center at Columbia University under the direction of Professor
Nikolas Themelis. The results of that study are summarized in this article.
GHG benefits of single-stream
The major contributor to GHG benefits of single-stream over dual-stream collection is
the increased rate of recycling and the corresponding increase in production of recyclable
commodities by a single-stream materials recovery facility (MRF). The increased produc-
tion of recyclable materials at the MRF leads to a decrease in GHG emissions because
recycled commodities replace virgin supplies, which have a higher carbon footprint. The
major contributor to the GHG benefit of the commingled products is fiber, followed by
aluminum and plastics, as is shown in Table 1.
Reprinted from
14 RR | December 2010

2. RR | December 2010 15
In comparative lifecycle assessment
(LCA) studies, it’s necessary to define the
boundaries around the system under inves-
tigation – in this case, the report focuses
primarily on the municipal collection and
MRF processing of recyclables and does
not include the post-processing or market-
side of the recycling system. That said,
the study took into account all fuel and
electricity usage, both at the collection and
processing stages of the dual- and single-
stream programs, and used these quanti-
ties to develop the overall environmental
impact assessment. It was also necessary to
include the environmental benefits gained
through the avoidance of the mining and
processing of virgin materials that are
replaced by recycled material as a result of
increased recovery rates.
What is being
measured?
The primary benefit of
switching to single-stream
collection will come as no
surprise to readers of this
article or the study – that,
on average, single-stream
increases the tonnage of
recyclables collected in a
community by 50 percent.
This does not happen in a
vacuum, of course, instead
due to the larger cart neces-
sitated by the switch, ease of
compliance for the commu-
nity, and the attendant ex-
pansion of materials included
with curbside pickup.
Speaking of pickup, the GHG impacts
of collection change, as well, with ease of
collection (automated collection requires
less time per pick-up, thus, less fuel burned
while idling); number of collections per
week and truck load (a higher loading on
the truck reduces overall distance to be
travelled, but increases the work load on
the truck’s engine); distance travelled by
collection trucks directly to the MRF or
transfer station; the distance between a
transfer station and MRF; and, number
of truck trips required at full operating
capacity.
Dual-stream collection systems that
use a two-compartment truck to collect
fiber and mixed plastic, metal, and glass
(PMG) in different compartments suffer
collection inefficiencies from the different
densities of the two streams. The PMG
compartment of these trucks fills much
more rapidly than the fiber compartment
because of the lower bulk density of rigid
containers.
There is, of course, an increase in
the residue – in the case of the study, a
doubling of the residue is assumed, from
five percent of each ton for dual-stream
collection to 10 percent of residue per ton
of single-stream collection. This is taken
into account for all the GHG assessment
equations.
The benefits of recycling versus
landfilling were studied, as well, using
a combination of the Environmental
Benefits Calculator created by the U.S.
Environmental Protection Agency (EPA),
and modified by the National Recycling
Coalition, and a GHG environmental
benefit calculator created by the Northeast
Recycling Council (NERC) under the
sponsorship of the EPA.
Where are the GHG
savings coming from?
Using recycled materials in place of virgin
materials is the primary source of reduction
of GHG impact, with differing impacts,
depending on the material and depend-
ing on its comparative effect if landfilled,
instead of recycled. Aluminum experiences
the greatest reduction of energy use when
comparing virgin to recycled materials,
because of the energy-intensive process of
making the metal from bauxite ore. Mixed
paper is the second largest GHG contribu-
tor when landfilled, mainly due to the fact
that paper degrades in landfills and emits
methane – some of which may not be cap-
tured – and has 21 times the global warm-
ing potential as carbon dioxide (CO2
), as is
detailed in Table 2.
A switch from dual- to single-stream
Table 1 | Summary of GHG benefits of
implementing single-stream (SS)
collection and processing
Material
Tons of
material per
outbound ton
from SS MRF*
Reduction in GHG
emissions, MTCE**
per ton of material
Reduction in GHG
emissions, MTCE**
per outbound ton
of SS MRF
Paper fiber 0.65 0.8 0.52
Ferrous metal 0.032 0.5 0.016
Aluminum 0.008 4.0 0.032
Plastics 0.08 0.4 0.032
Total GHG benefit per metric ton of MRF product = -0.61
*plus residue and glass
**Metric tons carbon equivalent 1 MTCE = 3.67 metric tons of carbon dioxide
Source: Earth Engineering Center, Columbia University, 2010
Table 2 | GHG benefit of using recycled materials1
Recyclable commodities
Tons
recycled
Reduction in energy use
for materials produced
from recycled rather than
“virgin” stock (mill. Btu)
Reduction in
GHG by using
recycled stock
(MTCE)2
Paper fiber (OCC, ONP, mixed) 1 -13.95 t-0.83
Iron and steel scrap 1 -19.97 -0.49
Glass 1 -2.13 -0.08
Mixed Plastics (HDPE, LDPE,
and PET)
1 -52.50 -0.41
Aluminum 1 -206.42 -4.03
(1) http://www.nrc-recycle.org/environmentalbenefitscalculator.aspx
(2) MTCE: metric tons of carbon equivalent; 1 MTCE = 3.67 metric tons of carbon dioxide
Source: Earth Engineering Center, Columbia University, 2010

3. 16 RR | December 2010
Figure 1 | Rate of growth of SS MRFs in the U.S.
(based on data compiled during the
EEC study)
Source: Earth Engineering Center, Columbia University, 2010
Table 3 | Assumed distribution of
products in MRF outbound
stream
Material
Percent distribution in outbound
stream from MRF (by mass)
Paper fiber 65%
Glass 12%
Residue 11%
Plastics (HDPE, PET, etc) 8%
Ferrous metal 3.20%
Aluminum 0.80%
Total 100%
Source: Earth Engineering Center, Columbia University, 2010
Table 4 | Estimated GHG benefits per
ton of MRF product
MRF Products
Avoided GHG per ton
of material (MTCE)
Paper fiber 0.8
Iron and steel 0.5
Aluminum 4.0
Plastic 0.4
Glass 0.1
Source: Earth Engineering Center, Columbia University, 2010
collection and processing
also generally results in a
smaller truck fleet, fewer
truck trips, heavier loads
on trucks, and lower use
of fuel per ton of material
collected. Table 4 shows
that, because of the higher
energy efficiency of single-
stream collection, the
change from dual- to sin-
gle-stream collection will
result in a lower carbon
footprint by -0.006 tons of
CO2
per ton of prior dual-
stream collection.
What’s in
a MRF?
The study used a 2006
Governmental Advisory
Associates (GAA) survey of
563 U.S. MRFs and found
that single-stream MRFs,
with an average capac-
ity of 206 tons per day,
represented 42 percent of the total U.S. MRF capacity.
Dual-stream MRFs, for comparison, averaged 152 tons
per day. The capacity of single-stream MRFs is doubtlessly
higher today, with the increased growth rate those MRFs
are currently enjoying, as seen in Figure 1. According to
some industry
experts, single-
stream MRFs
now total over
50 percent of
U.S. processing
capacity.
There are
over 545 mate-
rials recovery fa-
cilities (MRFs)
in operation
throughout the
U.S., with over
85 percent of
all MRF processing capacity dedicated to the processing
of single- or dual-stream recyclables. The biggest percent-
age of MRFs can be found in the South, at 28 percent,
followed by the Northeast (27 percent), the Midwest (25
percent) and the West (20 percent). However, the North-
east produces the highest average per-day throughout of
any of the nation’s four regions, at 23,238 tons per day.
Fifty percent of all MRFs operating in the U.S. employ the
use of automated sorting systems to process recyclables.
The other half rely on low-tech, labor-intensive methods to
process recovered material.
Considerable savings in energy consumption were also
found in a single-stream MRF – 0.3 kilograms (kg) of CO2
per ton processed, versus 11.4 kg for dual-stream process-
Successful conversion
from a dual-stream to
a single-stream system
can result in a GHG
benefit of 0.9 tons
of CO2e
per ton
of original dual-
stream collection.
0
50
100
150
200
250
NumberofSSMRF
20102005200019951990

4. RR | December 2010 17
ing. Taking into account the 50 percent
average increase in the volume of recyclable
materials, the energy advantage of single-
stream nearly compensates for the energy
requirement of the increased tonnage. This
scenario results in decreasing the GHG
emissions of the single-stream operation by
1.1 kg of CO2
per ton of material pro-
cessed.
As noted before, the major GHG ben-
efit of the single-stream switch is derived
from the increase in materials recovery and
the total GHG benefit amounts to 0.61
metric ton carbon equivalent (MTCE) per
ton of material processed at the MRF.
Table 5 | Community case studies for Comparison of Greenhouse Gas
Impacts of Dual Stream vs. Single Stream Collection and
Processing of Recyclables
Observations
Community Population Changes made Comments
Increasein
recyclingtons
Decreasein
GHGimpact
Costsavings
Avon, MA 4,500
Plant retrofitted to facilitate both
SS and DS operations
SS tonnage increased from 1,000 to
5,000 in 12 months
YES 9.40% YES
Springfield,
MA
151,000
SS collection Pilot Program for 800
households
expanding the plan to an additional
14,000 households
100% YES YES
West New
York, NJ
46,000 Switched to SS
No automatic collection due to high
population density
NO NO NO
Chula Vista,
CA
221,000
Switched from 4 stream collection
to SS, 18 gallon containers replaced
by 96 gallon carts
Recycling rates more than doubled to
1,500 tons per month
> 100% YES YES
Hopkins, MN 17,000
Weekly DS in 18 gallon open bins
to bi-weekly SS in wheeled carts
with lids
Net cost of collection decreased by
$ 20, 500 per year
16% YES YES
Dakota
County, MN
390,000 Has five SS and two DS communities Not a before and after scenario 16.60% YES YES
Madison, WI 230,000
Automated refuse collection
system and switched to SS
Worker’s compensation cost decreased
by 70% due to decrease in job related
injuries; Collection cost decreased by 53%
29% YES YES
Kent, MN
Mankato,
MN
33,000 Applied a feasibility model for SS YES YES
$ 33.76/
ton
Blaine, MN 55,000 Switched to SS
Collection truck productivity increased by
71%; Fuel consumption decreased by 40%
89% YES YES
Burnsville,
MN
60,000 Switched to SS
Collection truck productivity increased by
40%; Fuel consumption decreased by 40%
6% YES YES
Vadnais
Heights, MN
2,800
households
Switched to SS
Total miles travelled for collection
decreased by 52%
YES YES YES
East Grand
Forks, MN
8,000
Transition from SS in a bin
to SS in a cart
58% YES YES
Miami-Dade Switched to SS 92% YES YES
Collier
County, FL
315,000 Switched to SS
Very high collection for an year
after the switch
47% YES YES
Township of
Ocean, NJ
28,000 Switched to SS YES YES
$140,000
pa
Source: Earth Engineering Center, Columbia University, 2010

5. 18 RR | December 2010
GHG conclusions
Though the study did find an overall
savings of GHG emissions, single-stream
facilities have a more complicated GHG
footprint that requires accounting of
electricity use (and GHG-intensity of the
regional power grid), as well as on-site
combustion of natural gas, propane (i.e., in
forklifts and other vehicles), and diesel fuel.
That stated, the more advanced sorting
systems employed in single-stream MRFs
also allow municipalities to collect more,
and different types of, recyclable mate-
rial, which provides a source of recycled
products previously unavailable to end-use
mills.
Benefits at various levels of mea-
surement of single-stream collection of
recyclable materials over its dual-stream
counterparts, though the most salient, as
has been repeated here, is in the increased
volume of recycled materials collected.
Ultimately those extra volumes equate, ulti-
mately, to a reduction of GHG emissions
over the impacts of virgin materials, and
that’s a good thing.
Still to be accomplished are similar
unbiased looks at the long-term benefit
analysis of the increased tonnage to revenue
generation, collection system capital sav-
ings (which is significant), regional macro-
economic benefit of jobs and infrastructure
from diversion, not to mention savings in
landfill life. Further, though rightfully
concerning affected end user industries,
comparing those benefits to downstream
commodity consumer costs for cleaning
more diverse streams will continue to be of
a concern to the recycling community. It
is clear the system benefits overall but the
impact does make cleaning more diffi-
cult. Although tantalizing, these were not
directly addressed in the study and need
further vetting.
Richard Abramowitz is the director of pub-
lic affairs of Waste Management Recycle
Services and can be contacted at rabramo
witz@wm.com. Michael Timpane, director
of municipal recycling and diversion at
Waste Management can be contacted at
mtimpane@wm.com.
Reprinted with permission from Resource
Recycling, P.O. Box 42270, Portland, OR
97242-0270; (503) 233-1305, (503) 233-
1356 (fax); www.resource-recycling.com.
Table 6 | Summary of GHG benefits (-)
and impacts (+) of change from
DS to SS system
Contributing stage:
Metric Tons of CO2e per ton
of DS collection
Collection of recyclables -0.006
Processing of recyclables in MRF -0.001
Effect of increased rate of recycling -0.894
Total Impact on GHG footprint -0.901
Source: Earth Engineering Center, Columbia University, 2010