|Fig. 1: Recycling bins are easily accessible on university campuses.|
You would probably agree that the general attitude of society toward recycling is positive. However, we seem to only have some vague sense that recycling allows us to "save the planet" and makes us feel morally upright without really knowing the details. That is why the aim of this write-up is meant to give readers a more informed view of recycling.
The United States Environmental Protection Agency reveals that in 2012, the US recycled and composted 87 million tons of waste, which is 34.5 percent of the total amount discarded. That is a lot of waste recycled! Unfortunately, that also means that a lot of our waste was not recycled, about 164 million tons. 
For a moment, let us pretend that everything in the municipal waste system was actually pure, usable energy. To do an energy calculation, we first convert the amount of trash from tons to kilograms, then multiply by the chemical potential of different materials (joules/kg). We are left with a certain number of joules. Let us do an example with paper, because paper and paper products make up the largest percentage (27.4 percent) of municipal solid waste.  The 68.8 million tons of discarded paper is roughly 6.88 × 1010 kilograms. The chemical potential of paper (i.e. wood) is 2.0 × 107 joules/kg. Therefore, 68.8 million tons of paper is like discarding 1.38 × 1018 joules of energy. If we extend this calculation to the other categories of the 251 million tons of waste (by percentage: food 14.5, plastics 12.7, rubber/leather/textile 8.7, metals 8.9, yard trimmings 13.5, wood 6.3, glass 4.6, other 3.4), we get a grand total of approximately 5.5 × 1018 joules of energy. This seems to be a large number, but is actually only 1 percent of the energy budget of the world -- 5.0 × 1020 joules. 
Although the theoretical amount of energy we save if we could turn all the trash into usable energy is not substantial on a large scale, I think it is valuable to see the energy potential of what some may view as nothing more than garbage. Furthermore, there are other ways of looking at energy in the context of recycling. Sally Walker, senior researcher at the Genuine Progress Index Atlantic, a group that quantifies hard-to-measure realities like the benefits of recycling, claims "It takes three or four or even more times as much energy to make something from raw materials than from recycled."  Articles by Popular Mechanics and CNN seem to agree and tabulate energy saved by recycling compared to manufacturing from virgin materials. Up to 96 percent of energy is saved by recycling aluminum, between 76 and 88 percent for plastics, and 45-64 percent for paper. [4,5] These savings translate to some exciting numbers on a smaller scale. For example, recycling one ton of paper could "save the energy equivalent of 165 gallons of gasoline" and recycling a ton of aluminum cans conserves the same amount of energy in 26 barrels of oil. And if we recall the 87 million tons recycled in 2012, we find that the amount of energy saved is the same amount of energy consumed by nearly 10 million U.S. households in a year. 
These numbers show that recycling is one way for society to live more sustainably. Moreover, recycling and its processes are more environmentally friendly. Tom Zeller of the National Geographic writes, "A product's true cost includes greenhouse gases emitted in its creation as well as use, and pollutants that cause acid rain, smog, and fouled waterways." One may argue that the carbon footprint of recycling plants and their transportation and processes equal or exceed the costs of simply disposing of materials. However, an international study published by the Waste & Resources Action Programme looking at 180 municipal waste management systems found that in 83 percent of cases, "recycling proved better for the environment than burying or burning waste." 
While recycling may not be able to provide a large percentage of the global energy budget, it is still a proven way to be environmentally friendly and cognizant of our limited energy resources. So now, let us go forth with a more informed view of why recycling is helping to "save the planet."
© Alyssa Fujimoto. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 "Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2012," U.S. Environmental Protection Agency, EPA-530-F-14-001, February 2014.
 "BP Statistical Review of World Energy," British Petroleum, June 2014.
 S. Leahy, "Study: Recycling Cost Overstated," Wired, 13 Sept 04.
 A. Hutchinson, "Recycling By the Numbers: The Truth About Recycling," Popular Mechanics, 13 Nov 08.
 R. Oliver, "All About: Recycling," CNN, 4 Feb 08.
 T. Zeller, "Recycling: The Big Picture," National Geographic, January 08.