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Throughout this book, we have examined systems in terms of inputs, outputs, and internal changes. We will begin our discussion of solid waste in the same way—by considering the inputs and outputs of materials that end up becoming solid waste. We will define solid waste and examine the contents of the waste stream and waste generation trends. We will conclude the module with an examination of electronic waste and the specific challenges that it raises.

Learning Objectives

After reading this module, you should be able to

Humans are the only organisms that produce waste others cannot use. To explore this further, we need to learn why materials generated by humans become waste and what that waste contains. Although this seems like a trivial and simple question, it touches upon recent U.S. history, human behavior, and many other topics, including some that go beyond environmental science. We need to establish that waste can be viewed as a system, just like other materials. And it is necessary to describe how we got here—what features of U.S. society allowed us to generate the quantities of waste that we do.

Waste as a System

In an ecological system, plant materials, nutrients, water, and energy are the inputs. In a human system, inputs are very similar but contain materials manufactured by humans as well as natural materials. Within this system, humans use these inputs and materials to produce goods. And, as in any system, outputs are generated. We call these outputs waste, which is defined as material outputs that are not useful or are not consumed. Energy waste is also an output. FIGURE 51.1 shows a diagram of the relationship between inputs and outputs in a human system.

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If waste is the nonuseful output of a system, how do we determine what is useful? The detritivores we described in Chapter 3 recycle waste from animals and plants; they use the energy and nourishment they obtain and turn the remainder into compost or humus that nourishes other organisms. Dung beetles, for example, live on the energy and nutrients contained within the dung of elephants and other animals; in the natural world, this is not waste, it is food (FIGURE 51.2). Even humans make use of animal waste—for fertilizer, heat, and cooking fuel. In most situations, the waste of one organism becomes a source of energy for another.

The Throw-Away Society

Until a society becomes relatively wealthy, it generates little waste. Every object that no longer has value for its original purpose becomes useful for another purpose. In 1900 in the United States, virtually all metal, wood, and glass materials were recycled, although no one called it recycling back then. Those who collected recyclables were called junk dealers, or scrap metal dealers. For example, if a wooden bookcase broke and it could not be repaired, the pieces could be used to make a step stool. When the step stool broke, the wood was burned in a wood stove to heat the house. After World War II and with the rapid population growth that occurred in the United States, consumption patterns changed. The increasing industrialization and wealth of the United States, as well as cultural changes, made it possible for people to purchase household conveniences that could be used and then thrown away. Families were large, and people were urged to buy “labor-saving” household appliances and to dispose of them as soon as a new model was available. Planned obsolescence—designing a product so that it will need to be replaced within a few years—became a typical characteristic of everything from toasters to cars. TV dinners, throw-away napkins, and disposable plates and forks became common. In the 1960s disposable diapers became widely available and eventually replaced reusable cloth diapers. The components of household materials also changed. Objects were more likely to contain mixtures of different materials, which makes them harder to use for another purpose and difficult to recycle. The United States became the leader of what came to be known as the “throw-away society.”

Refuse collected by municipalities from households, small businesses, and institutions such as schools, prisons, municipal buildings, and hospitals is known as municipal solid waste (MSW). The Environmental Protection Agency (EPA) estimates that approximately 60 percent of MSW comes from residences and 40 percent from commercial and institutional facilities. Other kinds of waste generated in the United States in addition to MSW include agricultural waste, mining waste, and industrial waste. Waste other than MSW is typically deposited and processed on-site rather than transferred to a different location for disposal. Although some of these other categories generate a much greater percentage of yearly total solid waste, this chapter focuses on MSW.

FIGURE 51.3 shows the trend toward greater generation of MSW both overall and on a per capita basis from 1960 to 2011. In the first 47 years of this period, the total amount of MSW generated in the United States increased from 80 million metric tons (88 million U.S. tons) to 227 million metric tons (250 million U.S. tons) per year. In the last several years for which there are data, the total amount of MSW actually decreased by a small amount. The increase for all but the last several years can be explained in part because of population growth and in part because individuals have been generating increasing amounts of MSW. In 2011, average waste generation was 2.0 kg (4.4 pounds) of MSW per person per day. Waste generation varies by season of the year, socioeconomic status of the individual generating the waste, and even geographic location within the country.

Waste generation in much of the rest of the world stands in contrast to the United States. In Japan, for example, each person generates an average of 1.1 kg (2.4 pounds) of MSW each day. The 2010 UN-HABITAT estimate for the developing world is 0.55 kg (1.2 pounds) per person per day. The estimate for the developed world ranges from 0.8 to 2.2 kg (1.8–4.8 pounds) per person per day. Some indigenous people create virtually no waste per day, with as much as 98 percent of MSW being used for something by someone. The remaining 2 percent ends up in a landfill or waste pile. Even there, impoverished people scavenge and reuse some of the discarded material (FIGURE 51.4).

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Developing countries have become responsible for a greater portion of global MSW, in part because of their growing populations. In addition, as developing countries produce more of the goods used in the developed world, they generate more waste in the production process for these goods. For example, computers sold to consumers in the United States are assembled in such places as Taiwan, Singapore, and China, and the waste products generated are disposed of at the manufacturing location.

We have seen that MSW is made up of the things we use and then throw away. The goods that we use are generally a combination of organic items, fibers, metals, and plastics made from petroleum. A certain amount of waste is generated during any manufacturing process. Waste is also generated from the packaging and transporting of goods.

Depending on the particular materials, products, and goods that consumers use, such items can remain in the consumer-use system for a long time. For example, a ceramic plate or drinking mug might last for 5 to 10 years. In most cases, a disposable paper cup leaves the system within minutes or hours after it is used. Ultimately, all products wear out, lose their value, or are discarded. At this point they enter the waste stream—the flow of solid waste that is recycled, incinerated, placed in a solid waste landfill, or disposed of in another way. In this section we will look at the composition of MSW and then explore e-waste in more detail.

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Composition of Municipal Solid Waste

FIGURE 51.5a shows the data for MSW composition in the United States in 2011 by category before any recycling has occurred. The category “paper,” which includes newsprint, office paper, cardboard, and boxboard such as cereal and food boxes, made up 30 percent of the 227 million metric tons (250 million U.S. tons) of waste generated before recycling. The fraction of paper in the solid waste stream has been decreasing; less than a decade ago it was 40 percent of MSW. Organic materials other than paper products make up another large category, with yard waste and food scraps together making up 28 percent of MSW. Wood, which includes construction debris, accounts for another 6 percent. So, not including paper products, which are more easily recycled, roughly 34 percent of current MSW could be composted, although some wood construction debris is difficult to compost because of its size and thickness. The combination of all plastics makes up approximately 13 percent of MSW.

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As FIGURE 51.5b shows, 35 percent of the material that could potentially end up in a landfill or an incinerator is recovered. More than half of the recovered material is paper. Yard trimmings account for another large portion of recovered material, 22 percent.

After roughly one-third of our MSW is recycled, the resulting 148 million tons (164 million U.S. tons) that do end up in the landfill or incinerator have a different composition. As FIGURE 51.5b shows, paper represents a much smaller part of the diagram than in FIGURE 51.5a, largely because paper is so easily and frequently recycled. Food waste becomes a large part of the diagram because there are fewer composting programs available in the United States. Plastic is another component that increases, from 13 percent before recycling to 18 percent after materials have been recycled, in part because of the difficulty of recycling certain plastics.

Long-term viability is another way to consider MSW: Durable goods will last for years, nondurable goods are disposable, and compostable goods are those largely made up of organic material that can decompose under proper conditions. Containers and packaging make up 30 percent of MSW and are typically intended for one use. Food and yard waste account for 28 percent, and nondurable goods such as newspaper, white paper, printed products like telephone books, clothing, and plastic items like utensils and cups are 21 percent of the solid waste stream. Durable goods such as appliances, tires, and other manufactured products make up 20 percent of the waste stream. In addition to considering waste by weight, there is sometimes merit in considering waste by volume, especially when considering how much can be transported per truckload and how much will fit in a particular landfill.

E-Waste

Electronic waste, or e-waste, is one component of MSW that is small by weight but very important and rapidly increasing. Consumer electronics, including televisions, computers, portable music players, and cell phones, account for roughly 2 percent of the waste stream. This may not sound like a large amount but the environmental effect of these discarded objects is far greater than their weight. The older-style cathode-ray-tube (CRT) television or computer monitor contains 1 to 2 kg (2.2–4.4 pounds) of the heavy metal lead as well as other toxic metals such as mercury and cadmium. These metals may eventually leach out of the bottom of the landfill into groundwater or surface water. The toxic metals and other components can be extracted, but at present there is little formalized infrastructure or incentive to recycle them. However, many communities have begun voluntary programs to divert e-waste from landfills.

In the United States, most electronic devices are not designed to be easily dismantled after they are discarded. It generally costs more to recycle a computer than to put it in a landfill. The EPA estimates that approximately 27 percent of televisions and computer products discarded in 2010 were sent to recycling facilities. Unfortunately, much e-waste from the United States is exported to China, where adults as well as some children separate valuable metals from other materials using fire and acids in open spaces with no protective clothing and no respiratory gear (FIGURE 51.6). So even when consumers do send electronic products to be recycled, there is a good chance that the recycling will not be done properly.