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Almost every schoolchild in the United States has heard the phrase “reduce, reuse, and recycle.” In recent years, composting has been added to the list of actions one should take before adding material to the waste stream. In this module we will examine the three Rs and composting.

Learning Objectives

After reading this module, you should be able to

Starting in the 1990s, people in the United States began to promote the idea of diverting materials from the waste stream with a popular phrase “Reduce, Reuse, Recycle,” also known as the three Rs. The phrase incorporates a practical approach to the subject of solid waste management, with the techniques presented from the most environmentally beneficial to the least (FIGURE 52.1).

Reduce

“Reduce” is the first choice among the three Rs because reducing inputs is the optimal way to achieve a reduction in solid waste generation. This strategy is also known as waste minimization and waste prevention. If the input of materials to a system is reduced, the outputs will also be reduced; in terms of waste, this means that when less material is used, there will be less material to discard. One approach, known as source reduction, seeks to cut waste by reducing the use of potential waste materials in the early stages of design and manufacture. In many cases, source reduction also increases energy efficiency because it means that manufacturing produces less waste to begin with and can minimize disposal processes. Since fewer resources are being expended, source reduction also provides economic benefits.

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Source reduction can be implemented both on individual and on corporate or institutional levels. For example, if an instructor has two pages of handout material for a class, she could reduce her paper use by 50 percent if she provides her students with double-sided photocopies. A copy machine that can automatically make copies on both sides of the page might use more energy and require more materials in manufacturing than a copy machine that only prints on one side, but with up to half the number of copies needed, the overall energy used to produce them over time will probably be less. Further source reduction could be achieved if the instructor did not hand out any sheets of paper at all but sent copies to the class electronically, and the students refrained from printing the documents.

Source reduction in manufacturing can happen in several ways. If the company creates new packaging that provides the same amount of protection to the product with less material, successful source reduction has occurred. Consider the incremental source reduction that occurred with purchasing music. Music compact discs were packaged in large plastic sleeves that were three times the size of the CD. Today, most CDs are wrapped with a small amount of plastic material that just covers the CD case. Many people no longer purchase CDs at all and instead download their music from the Web. Less wrapping on CDs is an example of source reduction on the corporate level. Not purchasing CDs at all is an example of source reduction on the individual level.

Source reduction can also be achieved by material substitution. In an office where workers drink water and coffee from paper cups, providing every worker with a reusable mug will reduce MSW. In some categorization schemes, this could be considered reuse rather than source reduction. Nevertheless, cleaning the mugs will require water, energy to heat the water, soap, and processing of wastewater. The break-even point, beyond which there are gains achieved by using a ceramic mug (though this depends on a variety of factors), might be approximately 50 uses. The break-even point is shorter for a reusable plastic mug, in part because less energy is required to manufacture the plastic mug and, because it is lighter, less energy is used to transport it. Source reduction may also involve substituting less toxic materials or products in situations where manufacturing utilizes or generates toxic substances. For example, switching from an oil-based paint that contains toxic petroleum derivatives to a relatively nontoxic latex paint is a form of source reduction.

All of these examples achieve a reduction in material use and, ultimately, material waste, without an additional expenditure of materials or energy. For that reason, reduction is the first “R”—and it is the most environmentally beneficial.

Reuse

Reuse of a product or material that would otherwise be discarded, rather than disposal, allows a material to cycle within a system longer before it becomes an output. In other words, its mean residence time in the system is greater. Optimally, no additional energy or resources are needed for the object to be reused. For example, a mailing envelope can be reused by covering the first address with a label and writing the new address over it. Here we are increasing the residence time of the envelope in the system and reducing the waste disposal rate. Or we could reuse a disposable polystyrene cup more than once, though reuse might involve cleaning the cup, which would add some energy cost and generate some wastewater. Sometimes reuse may involve repairing an existing object, which costs time, labor, energy, and materials.

Energy may also be required to prepare or transport an object for reuse by someone other than the original user. For example, certain companies reuse beverage containers by shipping them to the bottling factory where they are washed, sterilized, and refilled. Although energy is involved in the transport and preparation of the containers, it is still less than the energy that would be required for recycling or disposal.

We have noted that reuse is still common in many countries and that it was common practice in the United States before we became a “throw-away society.” However, it is still practiced in many ways that we might not think of as reuse. For example, people often reuse newspapers for animal bedding or art projects. Many businesses and universities have surplus equipment agents who help find a home for items no longer needed. Flea markets, swap meets, and even popular websites such as eBay, craigslist, and Freecycle are all agents of reuse. Reuse sometimes involves the expenditure of energy and generates waste. For example, in order to transport, wash, and sterilize the beverage bottles in the example previously cited, energy is expended and wastewater is generated. So reuse does have environmental costs that typically exceed reducing the use of something, but it is preferable to using new material.

Recycle

The third “R” is recycling, the process by which materials destined to become MSW are collected and converted into raw materials that are then used to produce new objects. We divide recycling into two categories: closed-loop and open-loop. FIGURE 52.2 shows the process for each. Closed-loop recycling, shown in FIGURE 52.2a, is the recycling of a product into the same product. Aluminum cans are a familiar example; they are collected, brought to an aluminum plant, melted down, and made into new aluminum cans. This process is called a closed loop because in theory it is possible to keep making aluminum cans from only old aluminum cans almost indefinitely; the process is thus similar to a closed system. In open-loop recycling, shown in FIGURE 52.2b, one product, such as plastic soda bottles, is recycled into another product, such as polar fleece jackets. Although recycling plastic bottles into other materials avoids sending the plastic bottles to a landfill, it does not reduce demand for the raw material—in this case petroleum—to make plastic for new bottles.

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Recycling is not new in the United States, but over the past 25 years it has been embraced enthusiastically by both individuals and municipalities in the belief that it measurably improves environmental quality. The graph in FIGURE 52.3 shows both the increase in the weight of MSW in the United States from 1960 to 2011 and the increase in the percent of waste that was recycled over the same period of time. Recycling rates have increased in the United States since 1975, and today we recycle roughly one-third of MSW. In Japan, recycling rates are more than 50 percent, and some colleges and universities in the United States report recycling rates of 60 percent for their campuses.

Extracting resources from Earth requires energy, time, and usually a considerable financial investment. As we have seen, these processes generate pollution. Therefore, on many levels, it makes sense for manufacturers to utilize resources that have already been extracted. Today, many communities are adopting zero-sort recycling programs. These programs allow residents to mix all types of recyclables in one container that they deposit on the curb outside the home or bring to a transfer station. This saves time for residents who were once required to sort materials. At the sorting facility, workers sort the materials destined for recycling into whatever categories are in greatest demand at a given time and offer the greatest economic return (FIGURE 52.4). The markets for glass and paper are highly volatile. While there is always a demand for metals such as aluminum and copper, demand for recycled newspapers fluctuates. When newspaper is in low demand, the single-stream sorting facility might pull out newsprint to sell or give to local stables for use as horse bedding. At other times, when demand for paper is higher, the newsprint might be kept with other paper to be recycled into new paper products.

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Nevertheless, because recycling requires time, processing, cleaning, transporting, and possible modification before the waste is usable as raw material, it does require more energy than reducing or reusing materials. Such costs caused New York City to make a controversial decision in 2002 to suspend glass and plastic recycling. This was a major shift in policy for the city, which had been encouraging as much recycling as possible, including collection of mixed recyclables—glass, plastic, newspapers, magazines, and boxboard—at the same time as waste materials. After collection, the recyclables were sent to a facility where they were sorted. According to city officials, the entire process of sorting glass and plastic from other recyclables and selling the material was not cost effective. In 2004, the recycling of all materials was reinstated in New York City. Today, the goal in most recycling programs is to maximize diversion from the landfill, even if that means collecting materials that have little economic value. However, many communities periodically have difficulty finding buyers for glass and plastic since the price paid for these materials fluctuates widely.

The New York City case is just one example of why recycling is the last choice among the three Rs. This doesn’t mean that we should abandon recycling programs. Not only does it work well for materials such as paper and aluminum, but it also encourages people to be more aware of the consequences of their consumption patterns. Nevertheless, in terms of the environment, source reduction and reuse are preferable. The environmental implications of recycling are considered further in “Science Applied 7: Is Recycling Always Good for the Environment?” that follows Chapter 17 on page 625

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While diversion from the landfill is usually referred to as the three Rs, there is one more diversion pathway that is equally important, if not more so. Organic materials such as food and yard waste that end up in landfills cause two problems. Like any material, they take up space, but unlike glass and plastic that are chemically inert, organic materials are also unstable. As we will see later in this chapter, the absence of oxygen in landfills causes organic material to decompose anaerobically, which produces methane gas, a much more potent greenhouse gas than carbon dioxide.

An alternate way to treat organic waste is through composting. Composting creates organic matter (humus) that has decomposed under controlled conditions to produce an organic-rich material that enhances soil structure, cation exchange capacity, and fertility. Vegetables and vegetable by-products, such as cornstalks, grass, animal manure, yard wastes (like leaves and branches), and paper fiber not destined for recycling are suitable for composting. Normally, meat and dairy products are not composted because they do not decompose as easily, produce foul odors and are more likely to attract unwanted visitors such as rats, skunks, and raccoons.

Outdoor compost systems can be as simple as a pile of food and yard waste in the corner of a yard, or as sophisticated as compost boxes and drums that can be rotated to ensure mixing and aeration. From the decomposition process described in Chapter 3, we are already familiar with the process that takes place during composting. In order to encourage rapid decomposition, it is important to have the ratio of carbon to nitrogen (C:N) that will best support microbial activity—about 30:1. While it is possible to calculate the carbon and nitrogen content of each material you put into a compost pile, most compost experts recommend layering dry material such as leaves or dried cut grass—normally brown material—with wet material such as kitchen vegetables—normally green material. This will provide the correct carbon to nitrogen ratio for optimal composting. Frequent turning or agitation is usually necessary to ensure that decomposition processes are aerobic and to maintain appropriate moisture levels—otherwise the compost pile will produce methane and associated gases and emit a foul odor. If the pile becomes particularly dry, water needs to be added. Although many people assume that a compost pile must smell bad, with proper aeration and not too much moisture, the only odor will be that of fresh compost in 2 to 3 months’ time (FIGURE 52.5).

Large-scale composting facilities currently operate in many municipalities in the United States. Some facilities are indoors, but most employ the same basic process we have described, though on a much larger scale. FIGURE 52.6 shows the process. Organic material is piled up in long, narrow rows of compost. The material is turned frequently, exposing it to a combination of air and water that will speed natural aerobic decomposition. As with household composting, the organic material must include the correct combination of green (fresh) and brown (dried) organic material so that the ratios of carbon and nitrogen are optimal for bacteria. Various techniques are used to turn the organic material over periodically, including the use of rotating blades that move through the piles of organic material or a front loader that turns over the piles. The respiration activity of the microbes generates enough heat to kill any pathogenic bacteria that may be contained in food scraps, which is typically a concern only in large municipal composting systems. If the pile becomes too hot, it should be turned more frequently. If the pile doesn’t become hot enough, operators should check to make sure their C:N ratio is optimal, or they should slow the turnover rate. Within a matter of weeks, the organic waste becomes compost. Large-scale municipal composting systems with relatively little mechanization and labor may take up to a year to create a finished compost.

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It is not necessary to have an outdoor space to compost household waste; composting is possible even in a city apartment or a dorm room. It is even possible to set up a composting system in a kitchen or basement. The very popular book Worms Eat My Garbage: How to Set Up and Maintain a Worm Composting System by Mary Appelhof has encouraged thousands of individuals across the country to compost kitchen waste using red wiggler worms. A small household recycling bin is large enough to serve as a worm box. As with an outdoor compost pile, a properly maintained worm box does not give off bad odors.

The composting process does take time and space. Source separation can be an inconvenience or, in some situations, not possible. Also, in certain environments, storing materials before they are added to the compost pile can attract flies or vermin. Finally, the compost pile itself can attract unwanted animals such as rats, skunks, raccoons, and even bears. But because compost is high in organic matter, which has a high cation exchange capacity and contains nutrients, it enhances soil quality when added to agricultural fields, gardens, and lawns.