Lowering Greenhouse Gas Emissions by Reducing the Frequency of Curbside Recycling
One of the most popular recycling services offered by local governments in North America is the weekly curbside collection of recyclables from residents. In 2007, more than 8,600 curbside recyclables collection programs were reported in the United States (Franklin Associates. Municipal Solid Waste in the United States: 2007 Facts and Figures. http://www.epa.gov/osw/nonhaz/municipal/msw99.htm).
Because of the current recession, recycling program managers are under increased pressure to reduce recycling program costs. An option that is growing in popularity is reducing the frequency of the residential curbside recycling service. As discussed in this article, this option provides another important benefit—namely, the reduction of greenhouse gas (GHG) emissions.
The SWANA Applied Research Foundation’s (ARF) Recycling Group decided to target this topic for investigation during Fiscal Year (FY) 2011 (July 2010 through June 2011). This article presents highlights from the research memorandum prepared for this project, which was conducted with input and guidance from the ARF Recycling FY2011 Group Subscribers listed in Table 1. (The SWANA Applied Research Foundation was founded in 2001 with the purpose of conducting collectively defined and funded applied research on pressing solid waste issues. It is funded by local governments and other organizations that contribute a “penny per ton” of waste managed to the foundation on an annual basis. For more information on the SWANA Applied Research Foundation, please contact Jeremy O’Brien, director of applied research, SWANA, 301-585-2898.)
Greenhouse Gas Emissions From Curbside Recycling
Depending on participation rates and type of service, a residential recyclables collection crew can typically serve on the order of 1,000 households per day. Since recyclables are generally collected on a weekly basis, each collection crew can serve on the order of 5,000 households in a five-day workweek.
Diesel fuel is by far the most common fuel for vehicles used to provide recyclables collection services. According to the United States’ Environmental Protection Agency (EPA), the carbon content of a gallon of diesel fuel is 2.778 kilograms per gallon. See PDF on Average Carbon Dioxide Emissions Resulting from Gasoline and Diesel Fuel.
Refuse and recyclables collection trucks typically average on the order of 25,000 miles per year. In addition, their fuel efficiency is on the order of 2.8 miles per gallon of diesel fuel. (Greening Garbage Trucks: New Technologies for Cleaner Air. New York, NC, INFORM, 2003.)
The Intergovernmental Panel on Climate Change (IPCC) guidelines for calculating emissions inventories require that an oxidation factor be applied to the carbon content to account for a small portion of the fuel that is not oxidized into carbon dioxide (CO2). For all oil and oil products, the oxidation factor used is 0.99 (i.e., 99% of the carbon in the fuel is eventually oxidized, while 1% remains unoxidized.)
To calculate the CO2 emissions from a gallon of fuel, the carbon emissions are multiplied by the ratio of the molecular weight of CO2 (44) to the molecular weight of carbon (12), i.e., 44/12 or 3.67. Using the IPCC guidelines, CO2 emissions from a gallon of diesel can be calculated as follows:
CO2 Diesel = 2.778 kilograms
x 0.99 x 3.67 = 10.1 kg/gallon
Assuming the recycling collection vehicles travel 25,000 miles per year and averages 2.8 miles per gallon, a recyclables collection vehicle will use 8,929 gallons of diesel fuel per year (25,000 miles / 2.8 mpg). As a result, it will emit 90.2 metric tons of CO2e (MTCO2e) per year (8,929 gal x 10.1 kg/gal / 1,000 kg/metric ton), which is equivalent to 24.6 metric tons of carbon equivalent (MTCE) per year. These assumptions and calculations are summarized in Table 2.
Lowering GHG Emissions in Charlotte, NC
In an effort to improve efficiencies and reduce costs, an increasing number of local governments are reducing the frequency of curbside collection from a weekly to a biweekly or monthly basis. This is often done in conjunction with converting the service to “single stream” recycling, which involves the collection of commingled recyclables in large, lidded, roll-out containers using automated or semi-automated collection vehicles.
The city of Charlotte, North Carolina, began collecting residential recyclables in a single stream fashion in July 2010 (FY2011). At the same time, the city reduced its collection frequency from weekly to biweekly collection and increased the types of materials accepted for collection to include empty aerosol cans and all plastics with the exception of plastic No. 6. A new, 96-gallon cart was provided to each residence to enable the change in service to be implemented. The city provides curbside recycling collection services through its contractor to approximately 208,000 residences and small businesses. (Recyclables collection services are provided under contract to the city by Inland Services Corp.)
Performance data regarding the city’s weekly bin-based and biweekly rollout-container-based recyclables collection services are provided in Table 3. As indicated, in converting from weekly to biweekly recyclables collection, the setout rate increased from 42% to 50%, while the pounds per set out increased from 15.1 to 33.4 pounds. Despite these increases, the city was able to increase the number of households served per crew per day from 967 to 1,156 due to the reduced time required to service each set out with the automated collection approach.
By increasing collection efficiencies (using the automated collection approach) and reducing the frequency of recyclables collection from weekly to biweekly, the city was able to reduce its service workforce by 25 collection crews. The city estimates that $15 million will be saved over five years through the implementation of the “single-stream” biweekly rollout container service for recyclables collection. (Boone, M. “New Recycling Bins Roll Out Next Month,” NewsChannel 36. February 9, 2010.)
The GHG impacts that are accruing in the city of Charlotte due to the conversion to biweekly recyclables collection are summarized in Table 4.
As indicated in Table 2, the CO2e emissions per gallon of diesel fuel are estimated to be 22.2 pounds per gallon. In providing bin-based curbside recycling services on a weekly basis, it was assumed that collection vehicles traveled an average of 25,000 miles per year. (The city reports that the collection vehicles of its contractor—Inland Services Corp.—travel an average of 2,550 miles per month, or 30,600 miles per year—while providing the biweekly residential recyclables collection services. Due to the higher amounts of recyclables collected, it is assumed that these vehicles make more trips to the county’s material recycling facility than were made by the city vehicles providing the weekly, bin-based service. Therefore, it was assumed that the city vehicles traveled the lower, more typical distance of 25,000 miles per year.) Based on the average fuel efficiency of 2.8 miles per gallon reported by the city for recycling vehicles, it was estimated that each vehicle consumed 8,929 gallons per year in providing the weekly collection service. As a result, each vehicle emitted a little over 99 tons of carbon dioxide per year.
As stated above, by increasing collection efficiencies and reducing the frequency of recyclables collection, the city was able to reduce its service workforce by 25 collection crews and, therefore, was able to take 25 collection vehicles out of service. This resulted in a reduction of 2,255 MTCO2e or 615 MTCE per year.
Due to their low fuel efficiencies and daily use, recyclables collection vehicles represent a significant local source of GHG emissions.
The city of Charlotte estimates that it will save about $15 million over a five-year period due to the implementation of a single-stream recyclables collection system that allowed the city to reduce the residential recyclables collection frequency from a weekly to a biweekly basis. The city was also able to reduce its carbon footprint by 615 MTCE per year.
In addition to saving costs, increasing recycling and reducing fuel usage, GHG reductions are another important reason for considering the implementation of single-stream and other collection methods that enable the frequency of residential recyclables collection to be reduced.
Author's Bio: Jeremy K. O'Brien, P.E., is director of applied research for the Solid Waste Association of North America.
Author's Bio: Victoria O. Johnson is the solid waste services director for the city of Charlotte, NC.
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