Industrial Solid Wastes and Its Management

Solid Waste Treatment: Some Perspectives on Recycling

In 2010, Americans generated about 250 million T of municipal solid waste (MSW) (before recycling), an about 8% increase over 2000, an increase of 17% over 1990, and 36% over 1980 (USEPA 2002a, 2014). Thus, management of MSW continues to be an important challenge facing the United States and other highly industrialized nations in the twenty‐first century. Solid waste management is critical in the developing world, as well, where age‐old traditions of wasting nothing are often followed without regard to the significance and implications of the zero discharge concept.

Why Recycle?

Each ton of solid waste diverted from disposal, whether reused, recycled, converted in a waste‐to‐energy program, or composted, is one less ton of solid waste requiring disposal. To see the value of reusing, recycling, and composting solid waste, one need simply to consider the amount of disposal space required to accept that material. By implementing environmentally benign waste management strategies (as well as resource‐management strategies), a population can reduce its dependence on incinerators and landfills. And when recycled materials are substituted for virgin plastics, metal ores, minerals, glass, and trees, there is less pressure to expand the chemical, mining, and forestry industries. Supplying industry with recycled materials is preferable to extracting virgin resources from mines and forests not only because it conserves scarce natural resources but because it reduces dangerous air and water pollutants, such as GHG emissions, and saves energy.

Saving energy is an important environmental benefit of recycling because generating energy usually requires fossil‐fuel consumption and results in emissions that pollute the air and water. The energy required to manufacture paper, plastics, glass, and metal from recycled materials is generally less than the energy required to produce them from virgin materials. Additionally, the collection, processing, and transportation of recycled materials typically uses less energy than the extraction, refinement, transportation, and processing steps to which virgin materials must be subjected before industry can use them.

As is well known, a great amount of energy used in industrial processes and in transportation comes from the burning of fossil fuels. Recycling helps stem the dangers of global climate change by reducing the amount of energy used by industry, thus reducing GHG emissions, as well.

What Is Recycling

Recycling is the industrial process in which mechanical, chemical, and/or biological means are used to reprocess or convert materials in discarded products into recyclates, feedstock, or energy that can be used again. Recycling is more than a waste‐management strategy; it is also an important strategy for reducing the environmental effects of industrial production.

The aim of recycling is to close the loop of a material’s flow through the stages of manufacturing, marketing, consumption, and disposal. In closed‐loop recycling, an assigned set of operations is repeated in each of successive cycles and the operations vary according to the type of waste material being recycled. Thus, recycling is different from reuse, which is the further use, without any change in properties, of discarded products that have been recovered at the end of their service life.

There are three major ways of recycling waste materials:

1. Mechanical recycling, which can be divided into primary recycling, the in‐house processing of clean, single‐graded production offcuts into products equivalent in quality to the original items, and secondary (postconsumer) recycling, the reprocessing of discarded wastes from various sources into recycled products of inferior quality (for plastics and paper) or equivalent quality (for aluminum, glass, and metal) to the original items.
2. Tertiary or chemical or feedstock recycling processes, such as composting biodegradable wastes, transforming mixed plastics into monomer or low molecular weight oligomers in liquid or gaseous form, and application of mixed plastic flakes as a reduction agent for steelmaking.
3. Quaternary recycling processes, such as waste incineration with energy recovery, in which part of the energy content of combustible municipal or agricultural wastes is recouped and used, for example to raise steam (Brophy et al. 1997; Frisch et al. 1999; Mader 1997; Van Beukering 1999; Walker 1995).

Since recycling is an industrial process, its level of success depends highly on economic, technical, social, and political factors, which in turn vary greatly country to country (Bell 1998; Haque 1998). However, mechanical recycling of wastes is long‐established and tends to be the most popular practice in both the developed and developing parts of the world (Gandy 1994; Haque 1998; Shah 2000).

A Brief Overview of Recycling in the United States and United Kingdom

The history of primary recycling of discarded products, particularly of plastic scrap, goes back nearly as far as the industrial manufacture of products from virgin materials (Saba and Pearson 1995). In fact, waste management systems in New York City and London routinely collected for secondary recycling reusable items (mainly paper, cloth, glass bottles, and metals) from street‐cleaning enterprises, commercial premises, garbage dumps, and refuse transfer stations. The first refuse sorting plant in the United States opened in New York in 1898, and in the early 1920s London boasted a model sorting plant equipped with a long traveling belt from which recyclable materials could be removed (Gandy 1994).

In the years that followed World War II, planners who thought beyond the economic value of waste materials realized that recycling could reduce the volume of the wastestreams and that separation of incombustible glass and metals could increase the operational efficiency of incineration plants.

In the United States today, most locations recycle about 20–30% of their trash, approaching, meeting, or exceeding the national recycling target set decades ago. In the United Kingdom, wastes generated by commerce and industry are more readily recycled than domestic waste, a discrepancy reflecting the higher level of purity of the wastes of the former sector. The country recycles 25% of industrial wastes and 5% of domestic wastes (Haque 1998). The national government has set a revised target of 45% recovery of municipal wastes, including 30% recycling and composting, by 2010 (DETR 1999).

Schemes for waste collection and separation in both countries included providing households with outdoor receptacles for recycling, use of strategically located bottle and can banks, and sorting in a central material reclamation facility. Cans, paper products, glass, lead‐acid batteries, cars, and textile goods have well established recycling routes. In contrast, discarded plastic products and packaging – an increasing component of the wastestream – present many problems in recycling. Technical difficulties and high costs associated with identifying, separating, and recycling plastics of different types are compounded by the lack of markets for recyclate.

Recycling Today

Today in the United States and the United Kingdom, pressures for recycling arise largely from environmental concerns and from industrial policies minimizing consumption of energy and materials, aimed at lowering the raw materials and production costs. Further support for recycling activities is generated by concerns over the environmental pollution stemming from landfill and incineration, the conventional disposal treatments for solid waste.

Therefore, in many developed countries, the recycling of postconsumer waste is being actively encouraged by new legislation, as well as by economic incentives in place since the 1970s. A German law requiring retailers to take back their packaging has resulted in the availability of enormous quantities of material for recycling. Indeed, the success of this initiative created surpluses that depressed prices of recovered materials in Europe, thus hindering recycling efforts elsewhere. The German experience was perhaps anticipated by a former USEPA administrator, who called recycling “a good idea that has gone too far” (Bickerstaffe 1997).

In contrast to developed countries, the generation of waste per capita is substantially less than in less industrialized nations, which nevertheless post a recycling percentage for certain materials of close to 100%. Recycling was introduced to developing countries in the 1920s but did not take hold on a large scale until at least the late 1950s (Nahar 1990; Ratra 1994). From the start, these waste recycling systems have been driven by economic necessity, since the poor earn a living by scavenging discarded glass, plastics, paper, metals, and other materials which they then sell via an informal system for recycling in facilities that vary in their sophistication.

Recycling as a Route to Sustainable Productivity and Growth

Despite the massive recycling programs and pollution‐prevention efforts now under way, the amount of waste to be disposed of, as noted at the outset, is on the rise. We are using natural resources much faster than nature can replenish them. After we have used resources extracted from the Earth, we discard them, often in more harmful forms, into the same environment we depend on to provide air to breathe, water to drink, and soil to grow food. Concerns about this practice are voiced repeatedly and are well known.

Another concern that is related to waste, although it has broader ramifications as well, is community safety. The public is becoming more aware of how many tons of hazardous and nonhazardous materials alike are hauled over road, rail, and sea. Given the risk of accidents, especially when hazardous wastes are involved, the volume of transported substances continues to grow, concerns mount.

Plans for sustainable production and growth focus on leading the way to a future in which few materials and toxic substances will be required to support the needs of society, a future in which materials are reused or recycled rather than being incinerated, buried, or dumped. This shift will take place as we redesign processes, consumer and corporate behaviors, reuse more materials, and improve technologies. Industry, business, and government at all levels will need to capitalize on successful programs and invest in infrastructure and activities to meet these goals.

Interestingly, the economics of recycling is inversely related to the level of economic development of the recyclers, and in more general terms, the propensity to recycle is also inversely related to their socio‐economic status. In developed nations, facilities for reprocessing plastic wastes operate under known conditions and yield products of known quality. In developing countries, however, plastic wastes generally are recycled several times under undocumented conditions and exposed to the cumulative effects of extraneous contaminants. The deleterious effects on material quality of such uncontrolled and repeated processing are not hard to imagine. Thus, it is suggested that limits to the maximum number of times that plastics may feasibly be recycled vary with the socio‐economic conditions in different countries.