Understanding Plastics Recycling

1	All About the Waste

Empty plastic bottles, yesterday’s newspapers, eggshells, or used tea bags—all of these have one thing in common: they belong to municipal solid waste (MSW), ordinarily called “trash” or “garbage”. MSW refers to household, office, or retail waste and is part of everyone’s daily life. Each person in the United States generates 2 kg of MSW every day, which resulted in a total waste creation of 254 million tons (t)1 in 2013, and the trend is rising. As the volume of waste produced in the United States continues to increase, the handling and disposal of MSW are growing concerns of society. [1, 2, 3] In order to understand the impact of plastics and their recycling in the waste stream, it is important to understand the composition of MSW and current strategies for handling it.

1.1	Municipal Solid Waste—A Daily Companion

Municipal solid waste (MSW) is generally defined as nonhazardous waste. The United States Environmental Protection Agency (EPA) characterizes MSW as “waste consisting of everyday items, used and then thrown away, such as product packaging, bottles, food scraps and newspapers which comes from homes, schools, hospitals and businesses.” MSW is classified in three broad categories according to where it is generated: household waste, commercial waste, and institutional waste. [4, 5] Household waste includes that from single- and multiple-family homes, hotels and motels, and day-use recreation areas. This category accounts for 55 to 65 % of the total MSW generated and is also referred to as postconsumer waste. Thus, households are the primary source of MSW in the United States. Commercial waste includes solid waste from stores, offices, restaurants, warehouses, and other nonmanufacturing activities. Waste from schools, colleges, and similar public or quasi-public buildings is listed as institutional waste. The waste generated by the industrial sector is negligible. Manufacturing companies manage their solid residues or preconsumer waste by recycling, direct reuse, or self-disposal in industrial waste landfills. [1, 4, 5]

The total MSW generation in the United States increased steadily between 1960 and 2013, from 88 t/year (tons per year) to 254 t/year, due to economic expansion. The generation per capita per year has risen from 1.2 kg to 2 kg. However, it is important to note that after a peak in 2000, the MSW produced per capita per year has decreased slightly since then (2.15 kg to 2 kg). [2] Factors affecting the quantity of MSW generated include changes in population, individual purchasing power, product packaging, and technology, which again affect disposal habits as well as the nature of materials disposed. Hence, an analysis of the MSW composition over time is necessary to explain and also forecast future MSW generation in the United States. [4] The EPA uses two methods to characterize MSW, by material and by major products. In order to understand the studies presented in this book, knowledge of the proportion and quantity of different materials in MSW (Figure 1.1) is important and reflects the changes described in MSW generated in the United States.

Figure 1.1 provides information about the trends in consumer behavior and production of waste as seen, for example, in the significant change in the proportion of plastics in MSW between 1960 and 2013, which will be further discussed in Chapter 2. In this chapter we will discuss how the composition of MSW is of particular relevance for waste handling.

1.2	Management Methods for Municipal Solid Waste

The United States manages wastes in three different ways:

• Landfilling

• Incineration with energy recovery [waste-to-energy (WTE)]

• Recycling

Figure 1.2 shows a flowchart of this waste management system. Due to a growing awareness of environmental pollution, the EPA has strived to recycle as much MSW as possible or at least to burn it for energy, which will be further discussed in Chapter 3. It can be seen that residues from all waste treatment processes end up in landfill (dashed lines), which make disposal sites the final destination of MSW. [6, 7]

Changing technologies, waste compositions (Section 1.1), and regulations, together with this growing environmental awareness, has induced a change in MSW treatment in recent decades. In 1960, 94 % of the MSW generated in the United States was disposed of in landfills and afterwards open burned for volume reduction, which refers to burning garbage in outdoor pits. The remaining 6 % was recycled and the amount of energy recovered was insignificant. Since then, the amount of waste that is burned for energy recovery or recycled has increased steadily. In 2013, the majority of waste was still disposed of in U.S. landfills, but compared to the 1960s, it was only 52.9 %; 12.9% of MSW was burned with energy recovery and 34.2 % was recycled (Figure 1.2). [1, 2, 4, 8]

1.2.1

Landfilling

Landfill describes engineered areas of land used for the controlled deposit of solid waste onto or into land. The EPA distinguishes between three sizes of landfill, which are listed in Table 1.1. [9]

United States MSW landfills are required to comply with federal regulations contained in subtitle D of the Resource Conservation and Recovery Act (RCRA). The RCRA D requirements include siting restrictions in floodplains, surface and groundwater protection, disease and vector control, open-burning prohibitions, explosive gas (methane) control, fire prevention through the use of cover materials, and prevention of bird hazards to aircraft. [10, 11]

The United States mainly uses two different methods for active disposal of waste into landfills: the area fill method and the trench method. In the area fill method the waste is placed, spread out, and finally compacted in uniform layers using heavy equipment in large open sections of lined landfills. In the trench method, the waste is placed and compacted in a trench using material from the trench excavation as daily cover. The most appropriate method for a specific landfill is often determined by local conditions; a combination of both methods is possible. At the end of each day, cover materials are applied on top of the waste mass to prevent odors and fires, and to reduce litter, insects, and rodents. The daily cover material includes soil, compost, incinerator ash, foam, and tarps. If a landfill has reached its permitted height, the cell has to be closed. The required postclosure care period is 30 years, but it can be shortened or extended with changing state regulations and approvals. [4, 11, 12, 13, 14, 15]

Due to the described regulations, regularly amended by the EPA, opening a new or expanding an existing landfill plant has become increasingly difficult. After adoption of the first RCRA in 1968, the total number of landfills in the United States has steadily declined, especially small and private landfills. [1, 13]

Despite a decreasing number of landfills and a diminishing percentage of total MSW disposed of in landfills, the total waste capacity of landfills is still increasing due to the increasing amount of waste in general. The focus in the United States is on large and modern landfill plants. The fact that the combined capacity of the two largest landfill plants in the United States in 2014 was close to 10 billion t underlines this trend. [1, 13]

1.2.2

Incineration with Energy Recovery (Waste-to-Energy)

Incineration with energy recovery is the only waste-to-energy (WTE) technology that is commercially used in the United States. The heat generated by burning waste can be used directly for heating, to produce steam, or to produce electricity. In 2013, 12.9 % of the total MSW in the United States was burned with energy recovery. [16, 17]

The main motivation for burning waste was and still is the reduction of the volume and weight of solid waste. Nowadays, combustion decreases the volume of waste by...