The garbage that is managed by local governments is known as municipal solid waste (MSW). Specifically, MSW is waste generated by commercial and household sources that is collected and either recycled, incinerated, or disposed of in MSW landfills. The U.S. Environmental Protection Agency (EPA) separates MSW into several categories, including containers and packaging, yard wastes, durable goods, and nondurable goods. Examples of durable goods, which are designed to last longer than three years, include appliances, tires, batteries, and electronic equipment. Newspapers, clothing, disposable tableware, office paper, wood pallets, and diapers, which all have a lifetime of less than three years, are types of nondurable goods. MSW does not include domestic sewage and other municipal wastewater treatment sludges, demolition and construction debris, agricultural and mining residues, combustion ash, and wastes from industrial processes. These types of waste, known collectively as industrial solid waste, are largely excluded from hazardous waste regulation; programs addressing industrial solid waste are still in their infancy.
During the 1980s, solid waste management issues emerged in the United States due to the increasing amounts of solid waste generated, shrinking landfill capacity, rising disposal costs, and strong opposition to the siting of new solid waste facilities. This problem was illustrated by the much-publicized Mobro garbage barge, which traveled on a six-month odyssey before the garbage was finally disposed of in New York state, where it was originally generated.
With millions of households and businesses generating garbage in the United States, developing a national management program is challenging. Instead of federal regulations dictating how solid wastes should be managed, solid-waste programs are managed by states and municipalities on the local level according to individual community needs. With the exception of federally mandated landfill design and operating criteria to ensure the protection of groundwater and requirements for the federal purchase of products containing recovered materials, the EPA's role in implementing solid-waste management programs includes setting national goals, providing leadership and technical assistance, and developing educational materials.
The generation of MSW has grown steadily over the past thirty years, from 88 million tons per year, or 2.7 pounds per person per day in 1960, to 229.9 million tons, or 4.62 pounds per person per day in 1999. The largest component of the MSW stream is paper and paperboard products (38.1%), with yard trimmings the second most predominant component (12.1%). The top of two pie charts on the next page breaks down this waste by material category. While the generation of waste has grown steadily, so too have its recycling and recovery. In 1960 about 7 percent of MSW was recycled, and in 1999 this figure had increased to 27.8 percent. How MSW is managed is shown in the bottom of two pie charts on the next page. Although the majority of solid waste is still sent to landfills, statistics indicate that there is a clear trend away from reliance on this method. Combustion of MSW and recovery through recycling are now a common practice in the United States.
In response to mounting solid waste problems, EPA published The Solid Waste Dilemma: An Agenda for Action in 1989, which presents goals and recommendations for action by the EPA, state and local governments, industry, and consumers to address the solid waste problems facing the United States. The EPA recommends an integrated, hierarchical approach to waste management using four components: source reduction, recycling, combustion, and landfills. This comprehensive approach addresses critical junctures in the manufacture, use, and disposal of products and materials to minimize wastefulness and maximize value. This strategy favors source reduction to decrease the volume and toxicity of waste and to increase the useful life of products. After source reduction, recycling, including composting, is the preferred waste management approach to divert waste from combustors and landfills. Combustion is used to reduce the volume of waste being disposed as well as to recover energy, whereas landfills are used for the final disposal of nonrecyclable and noncombustible material.
The goal of the integrated management hierarchy is to use a combination of all these methods to handle the MSW stream safely and effectively with the least adverse impact on human health and the environment. The EPA encourages communities to develop community-specific assessments of potential source reduction, recycling, combustion, and landfill programs and to customize programs according to local needs, keeping in mind the strategies preferred in the national hierarchical structure. Because each community's waste profile (i.e., the amounts and types of waste generated), infrastructure, social and economic structure, and policies differ, decision makers at the local level are the most qualified to assess community needs and develop an appropriate solid waste management strategy.
Source reduction, also known as waste prevention, is a front-end approach to addressing MSW problems by changing the way products are made and used. It represents an attempt to move away from the traditional "end-of-the-pipe" waste management approach used in the past. Source reduction at the "beginning of the pipe" is defined as the design, manufacture, and use of products in a way that reduces the quantity and toxicity of waste produced when products reach the end of their useful lives. Waste-prevention activities include product reuse (e.g., reusable shopping bags), product material volume reduction (e.g., eliminating unnecessary product packaging), reduced toxicity of products (e.g., use of substitutes for lead, mercury, and other toxic substances), increased product lifetime (e.g., design of products with a longer useful life), and decreased consumption (e.g., changing consumer buying practices, bulk purchasing). In 1996 the EPA reported that 23 million tons of MSW had been source-reduced, approximately 11 percent of the 209.7 million tons of MSW generated that year. Businesses, households, and state and local governments all play an active role in implementing successful source reduction programs.
Recycling refers to the separation and collection of wastes and their subsequent transformation or remanufacture into usable or marketable materials. Recycling, including composting, diverts potentially large volumes of material from landfills and combustors, and prevents the unnecessary waste of natural resources and raw materials. Other environmental benefits offered by recycling include a reduction in greenhouse gas emissions, energy conservation, and the preservation of biodiversity and habitats that would otherwise be exploited for virgin materials. In addition, recycling programs create new manufacturing jobs, boost the economy, and facilitate U.S. competitiveness in the global marketplace.
Like any other part of the integrated waste management hierarchy, recycling programs should be carefully designed and implemented to address the needs of the community, including attention to their cost-effectiveness. Recycling collection and separation programs vary in degree of implementation: Some may be simple drop-off programs, whereas others may involve comprehensive curbside collection and complex source separation at a recovery facility. Successful recycling, however, requires more than the separation and collection of postconsumer materials. Recycling programs must identify and develop markets for recovered material; only when the materials are reused is the recycling loop complete.
Although markets and uses for recovered materials are constantly expanding, reuse opportunities will vary by material. For example, recycling options for plastic are contingent on the type of resin used. Soft drink bottles are currently incorporated into products such as carpeting, household cleaner bottles, and fiberfill for coats and pillows, whereas polystyrene food containers and cups are being recycled into insulation, cafeteria food trays, and children's toys. Depending on their condition, tires can be used for artificial reefs, playground equipment, floor mats, and road construction materials. Recycled-content newspapers, stationery, corrugated containers, and toilet paper are some examples of how discarded paper is recycled.
Recycling activities also include centralized composting of yard and food wastes. Composting refers to the controlled decomposition of organic matter by microorganisms into a stable humus material that is used primarily on the land to improve soil quality. Many communities conduct large-scale centralized composting of yard waste in an effort to save landfill capacity. Individuals are also helping to reduce waste by composting yard waste in their backyards, and by not bagging grass clippings or other yard wastes—these activities are actually classified as source reduction. The composting of yard waste has seen tremendous growth in the past ten years. In 1980 the amount of yard waste recovered was negligible (less than 5,000 tons, or 0.05%). By 1999 the amount of yard waste recovered had grown to 12.6 million tons, or 45.3 percent.
Burning has been a popular method of reducing the volume and odor of garbage for centuries. With the onset of the 1970s energy crisis and the Clean Air Act, a more sophisticated system of incineration was developed that could use waste as a fuel to produce energy. Modern combustion facilities no longer just destroy garbage, but instead are designed to recover energy that is used to produce steam and electricity. Developing a successful waste-to-energy system involves numerous decisions that will dictate whether such a project is effective in a given community. Over the past two decades communities have demonstrated an increased interest in combustion as a waste management option. Between 1980 and 1999, the combustion of solid waste increased 5.8 percent, with approximately 2.6 million tons of MSW burned in 1999. In addition to the benefits of energy recovery, combustion residues consume less landfill space; combustion ash amounts to approximately 25 percent (dry weight) of the MSW input. However, citizens often oppose the building of incinerators close to communities and farmland because of the perception of health risks due to emission of pollutants including mercury and dioxin that are toxic, persistent, and bioaccumulate.
Even with the use of source reduction, recycling, and combustion, there will always be waste that ultimately must be disposed of in landfills. According to the EPA's Municipal Solid Waste in the United States: 1999 Facts and Figures, landfill disposal still remains the most widely used waste management method (accounting for approximately 57.4% of the total). Many communities now face difficulties siting new landfills largely because of increased citizen and local government concerns about the potential health risks and aesthetics of situating a landfill in their neighborhoods. The EPA issued new technical standards for MSW landfills in 1991. These addressed several aspects of landfill management, including location restrictions, design and operating criteria, and groundwater monitoring. Even with national landfill standards, decreasing landfill capacity and the difficulties associated with the construction of new landfills remain significant issues.
The EPA has explored several solutions to conserving landfill capacity, including the viability of engineering materials such as plastics to be less resistant to degradation or, in other words, biodegradable. Biodegradable materials can be broken down into simpler substances (e.g., elements and compounds) by bacteria or other natural decomposers. Paper and most organic wastes such as food and leaves are biodegradable. In contrast, nonbiodegradable substances cannot be broken down in the environment by natural processes. In general, degradation in landfills occurs very slowly due to modern landfill design criteria, which minimize waste exposure to sunlight, air, and moisture. In fact, even biodegradable organic materials might take decades to decompose in a landfill; carrots and cabbage have been discovered in recognizable form after several years of burial. Studies indicate that biodegradable materials may help diminish risks to wildlife and aesthetic damage (i.e., discarded six-pack beverage rings and wrappers), but will not reduce the volume or toxicity of waste nor provide a solution to decreasing landfill capacity.
In continuing efforts to conserve landfill space and reduce waste toxicity, the EPA is currently investigating the potential benefits and drawbacks associated with the use of bioreactor landfills. Bioreactor landfills are designed to transform and more quickly stabilize the decomposable organic constituents of the waste stream through the controlled injection of liquid or air to enhance microbiological degradation processes. In other words, by controlling the moisture content, bioreactor landfills facilitate microbial decomposition of waste. Recent findings show that bioreactor landfills successfully expedite the degradation process (e.g., from decades to years), offer a 15 to 30 percent gain in landfill space, and may reduce postclosure care and leachate disposal costs. In addition, the bioreactor technology significantly increases landfill gas emissions, which are captured and often used beneficially for energy recovery. Due to their complexity, however, bioreactor landfills may be more costly, and concerns have been raised regarding increased odors, liner instability, and surface seeps. Working in conjunction with state and local governments and private companies, the EPA has initiated several research and pilot projects to examine the effectiveness of this innovative technology.
International Solid Waste Management
Because solid waste is generated everywhere, addressing the environmentally safe management of solid waste is not limited to the United States. Management strategies vary by country and region, although most programs address waste issues with models consisting of some combination of source reduction, combustion, recycling, and landfills. For example, the European Environment Agency (EEA) offers solid-waste management guidance analogous to EPA's integrated hierarchy. Specifically, the Community Strategy on Waste recommends that the agency's eighteen-member countries make waste prevention their top priority, followed by materials recovery, energy recovery, and, finally, the safe disposal of waste.
The international Organisation for Economic Co-operation and Development (OECD) compiles worldwide data, including environmental statistics, for its thirty member countries. The bar graphs on the next page compare the total amount of municipal waste generated annually and the annual amount of municipal waste generated per capita, respectively, by the United States and other selected OECD member countries in 1997. Per capita waste generation rates vary significantly by country; factors contributing to such discrepancies may include individual lifestyle and national economic structure. Although individual national definitions may differ, for the purpose of analysis here, OECD regards municipal waste as waste collected by or on the order of municipalities, including that originating from households, commercial activities, office buildings, institutions such as school and government buildings, and small businesses.
The environmentally safe management of municipal solid waste may always be an issue, simply because societies will continue to generate trash due to increasing populations and the growing demands of modern society. Working together, federal, state, and local governments, industry, and citizens have made substantial progress in effectively responding to solid waste issues through source reduction, recycling, combustion, and landfill programs. Such community-tailored programs provide possible long-term solutions to decreasing the amount of waste that is produced and ultimately placed in landfills.
see also Composting; Incineration; Landfill; Plastic; Recycling; Reuse; Waste; Waste Reduction.
christiansen, kim michael. (1999). waste annual topic update: 1998. copenhagen: european environmental agency.
o'leary, philip r., and walsh, patrick h. (1995). decision makers guide to solid waste management, vol. ii. washington, d.c.: u.s. environmental protection agency. epa530-r95-023.
organisation for economic co-operation and development. (1999). oecd environmental data: compendium 1999 edition. organisation for economic co-operation and development.
u.s. environmental protection agency. (1994). composting yard trimmings and municipal solid waste. washington, d.c.: u.s. environmental protection agency. epa530-r-94-003.
(top) comparison of annual amounts of msw generated by the united states and other selected oecd countries in 1997. generation amounts are in 1,000 tons. (bottom) comparison of annual amounts of msw generated per capita by the united states and other selected oecd countries in 1997. generation amounts are in kilograms per capita. (both based on statistics from oecd environmental data 1999.)
u.s. environmental protection agency. (1990). environmental fact sheet: the facts on degradable plastics. washington, d.c.: u.s. environmental protection agency. epa530-sw-90-017d.
u.s. environmental protection agency. (1990). environmental fact sheet: the facts on recycling plastics. washington, d.c.: u.s. environmental protection agency. epa530-sw-90-017e.
u.s. environmental protection agency. (1992). "green" advertising claims. washington, d.c.: u.s. environmental protection agency. epa530-f-92-024.
u.s. environmental protection agency. (1991). markets for scrap tires. washington, d.c.: u.s. environmental protection agency. epa530-sw-90-074a.
u.s. environmental protection agency. (1997). measuring recycling: a guide for state and local governments. washington, d.c.: u.s. environmental protection agency. epa530-r-97-011.
u.s. environmental protection agency. (2001). municipal solid waste in the united states: 1999 facts and figures. washington, d.c.: u.s. environmental protection agency. epa530-r-01-014. also available from http://www.epa.gov/epaoswer/non-hw/muncpl/mswfinal.pdf
u.s. environmental protection agency. (1999). national source reduction characterization report for municipal solid waste in the united states. washington, d.c.: u.s. environmental protection agency. epa530-r-99-034. also available from http://www.epa.gov/epaoswer/non-hw/reduce/r99034.pdf.
u.s. environmental protection agency. (1998). puzzled about recycling's value? look beyond the bin. washington, d.c.: u.s. environmental protection agency. epa530-k-98-008. also available from http://www.epa.gov/epaoswer/non-hw/recycle/benefits.pdf.
u.s. environmental protection agency. (1998). rcra orientation manual: 1998 edition. washington, d.c.: u.s. environmental protection agency. epa530-r-98-004.
u.s. environmental protection agency. (1999). recycling works! state and local solutions to solid waste management problems. washington, d.c.: u.s. environmental protection agency. epa530-k-99-003. also available from http://www.epa.gov/epaoswer/non-hw/recycle/recycle.pdf.
u.s. environmental protection agency. (1989). the solid waste dilemma: an agenda for action. washington, d.c.: u.s. environmental protection agency. epa530-sw-89-019.
Office of Solid Waste/U.S. Environmental Protection Agency
Solid waste is composed of a broad array of materials discarded by households, businesses, industries, and agriculture. The United States generates more than 11 billion tons (10 billion metric tons) of solid waste each year. The waste is composed of 7.6 billion tons (6.9 billion metric) of industrial nonhazardous waste, 2–3 billion tons (1.8–2.7 billion metric) of oil and gas waste, over 1.4 billion tons (1.3 billion metric) of mining waste, and 195 million tons (177 billion metric) of municipal solid waste .
Not all solid waste is actually solid. Some semi-solid, liquid, and gaseous wastes are included in the definition of solid waste. The Resource Conservation and Recovery Act (RCRA) defines solid waste to include garbage , refuse, sludge from municipal sewage treatment plants, ash from solid waste incinerators, mining waste, waste from construction and demolition, and some hazardous wastes. Since the definition is so broad, it is worth considering what the act excludes from regulations concerning solid waste: untreated sewage, industrial wastewater regulated by the Clean Water Act , irrigation return flows, nuclear materials and by-products, and hazardous wastes in large quantities.
RCRA defines and establishes regulatory authority for hazardous waste and solid waste. According to the act, some hazardous waste may be disposed of in solid waste facilities. These include hazardous wastes discarded from households, such as paint, cleaning solvents, and batteries, and small quantities of hazardous materials discarded by business and industry. Some states have their own definitions of solid waste which may vary somewhat from the federal definition. Federal oversight of solid-waste management is the responsibility of the Environmental Protection Agency (EPA).
Facilities for the disposal of solid waste include municipal and industrial landfills, industrial surface impoundments, and incinerators. Incinerators that recover energy as a by-product of waste combustion are called resource recovery or waste-to-energy facilities. Sewage sludge and agricultural waste may be applied to land surfaces as fertilizers or soil conditioners. Other types of waste management practices include composting , most commonly of separated organic wastes, and recycling . Some solid waste ends up in illegal open dumps.
Three quarters of industrial nonhazardous waste comes from four industries: iron and steel manufacturers, electric utilities , companies making industrial inorganic chemicals , and firms producing plastics and resins. About one-third of industrial nonhazardous waste is managed on the site where it is generated, and the rest is transported to off-site municipal or industrial waste facilities. Although surveys conducted by some states are beginning to fill in the gaps, there is still not enough landfills and surface impoundments for industrial solid wastes. Available data suggest there is limited use of environmental controls at those facilities, but there is insufficient information to determine the extent of pollution they may have caused.
The materials in municipal solid waste (MSW) are discarded from residential, commercial, institutional, and industrial sources. The materials include plastics, paper, glass, metals, wood, food, and yard waste ; the amount of each material is evaluated by weight or volume. The distinction between weight and volume is important when considering such factors as landfill capacity. For example, plastics account for only about 8% of MSW by weight, but more than 21% by volume. Conversely, glass represents about 7% of the weight and only 2% of the volume of MSW.
MSW has recently been the focus of much attention in the United States. Americans generated 4.5 lb (2 kg) per day of MSW in 2000, an increase from 4.3 lb (1.95 kg) per day 1990, 4.0 lb (1.8 kg) per day in 1980, and 2.7 lb (1.2 kg) per day in 1960. This increase has been accompanied by tightening federal regulations concerning the use and construction of landfills. The expense of constructing new landfills to meet these regulations, as well as frequently strong public opposition to new sites for them, have sharply limited the number of disposal options available, and the result is what many consider to be a solid waste disposal crisis. The much-publicized "garbage barge" from Islip, New York, which roamed the oceans from port to port during 1987 looking for a place to unload, has become a symbol of this crisis.
The disposal of MSW is only the most visible aspect of the waste disposal crisis; there are increasingly limited disposal options for all the solid waste generated in America. In response to this crisis, the EPA introduced a waste management hierarchy in 1989. The hierarchy places source reduction and recycling above incineration and landfilling as the preferred options for managing solid waste.
Recycling diverts waste already created away from incinerators and landfills. Source reduction, in contrast, decreases the amount of waste created. It is considered the best waste management option, and the EPA defines it as reducing the quantity and toxicity of waste through the design, manufacture, and use of products. Source reduction measures include reducing packaging in products, reusing materials instead of throwing them away, and designing products to be long lasting. Individuals can practice waste reduction by the goods they choose to buy and how they use these products once they bring them home. Many businesses and industries have established procedures for waste reduction, and some have reduced waste toxicity by using less toxic materials in products and packaging. Source reduction can be part of an overall industrial pollution prevention and waste minimization strategy, including recapturing process wastes for reuse rather than disposal.
Some solid wastes are potentially threatening to the environment if thrown away but can be valuable resources if reused or recycled. Used motor oil is one example. It contains heavy metals and other hazardous substances that can contaminate groundwater , surface water, and soils. One gallon (3.8 L) of used oil can contaminate 1 million gal (3.8 million L) of water, but these problems can be avoided and energy saved if used oil is rerefined into motor oil or reprocessed for use as industrial fuel. Much progress remains to be made in this area: of the 200 million gal (757 million L) of used oil generated annually by people who change their own oil, only 10% is recycled.
Another solid waste with recycling potential are used tires, which take up a large amount of space in landfills and cause uneven settling. Tire stockpiles and open dumps can be breeding grounds for mosquitoes, and are hazardous if ignited, emitting noxious fumes that are difficult to extinguish. Instead of being thrown away, tires can be shredded and recycled into objects such as hoses and doormats; they can also be mixed in road-paving materials or used as fuel in suitable facilities. Whole tires can be retreaded and reused on automobiles, or simply used for such purposes as artificial reef construction. Other solid wastes with potential for increased recycling include construction and demolition wastes (building materials), household appliances, and waste wood.
The EPA recommends implementation of this waste management hierarchy through integrated waste management. The agency has encouraged businesses and communities to develop systems where components in the hierarchy complement each other. For example, removing recyclables before burning waste for energy recovery not only provides all the benefits of recycling, but it reduces the amount of residual ash. Removing recyclable materials that are difficult to burn, such as glass, increases the Btu value of waste, thereby improving the efficiency of energy recovery.
Some state and local governments have chosen to conserve landfill space or reduce the toxicity of waste by instituting bans on the burial or burning of certain materials. The most commonly banned materials are automotive batteries, tires, motor oil, yard waste, and appliances. Where such bans exist, there is usually a complementary system in place for either recycling the banned materials or reusing them in some way. Programs such as these usually compost yard waste and institute separate collections for hazardous waste.
Perhaps because of the solid waste disposal crisis, there have been recent changes in solid waste management practices. About 55.3% of MSW was buried in landfills in 2000, down from 67% in 1990 and 81% in 1980. Recovery of materials for recycling and composting also increased, with 64 million tons of material diverted away from landfills and incinerators in 1999, up from 34 million tons in 1990.See also Refuse-derived fuel; Sludge treatment and disposal; Solid waste incineration; Solid waste landfilling; Solid waste recycling and recovery; Solid waste volume reduction; Source separation
[Teresa C. Donkin and Douglas Smith ]
Blumberg, L., and R. Grottleib. War on Waste—Can America Win Its Battle With Garbage? Covelo, CA: Island Press, 1988.
Neal, H. A., and J. R. Schubel. Solid Waste Management and the Environment: The Mounting Garbage and Trash Crisis. Englewood Cliffs, NJ: Prentice-Hall, 1987.
Robinson, W. D., ed. The Solid Waste Handbook. New York: Wiley, 1986.
Underwood, J. D., and A. Hershkowitz. Facts About U. S. Garbage Management: Problems and Practices. New York: INFORM, 1989.
Glenn, J. "The State of Garbage in America." Biocycle (May 1992).
U.S. Environmental Protection Agency. Characterization of Municipal Solid Waste in the United States: 1992 Update (Executive Summary). Washington, DC: U. S. Government Printing Office, July 1992.
U.S. Environmental Protection Agency. Solid Waste Disposal in the United States. Washington, DC: U.S. Government Printing Office, 1989.
solid waste, discarded materials other than fluids. In the United States in 1996, nearly 210 million tons—about 4.3 lb. (2 kg) per person daily (up from 2.7 lb./1.2 kg in 1960)—were collected and disposed of by municipalities. In that year, municipal garbage included 12.4 million tons of glass and about 80 million tons of paper and paperboard (by far the largest constituent); in addition enormous tonnages of food residues, yard trimmings, textiles, plastics, and sludge formed in sewage treatment were produced. Although the amount of the increase has been slowed somewhat by recycling and composting programs and improvements in packaging, the amount of solid waste continues to increase annually. Moreover, the most common disposal methods pollute land, water, or air to some degree (see pollution). Management of solid waste therefore presents an increasingly acute problem.
See also environmentalism; radioactive waste.
Approximately 62% of municipal waste is placed in landfills. If the waste is dumped untreated, it can promote the proliferation of rats, flies, and other vermin, encourage growth of disease-carrying organisms, contaminate surface and underground water, scar the land, and preempt open space. An alternative method of solid waste disposal is the sanitary landfill, first employed in Fresno, Calif., in 1937: waste is spread in thin layers, each tamped compactly and covered by a layer of earth. While more expensive than open dumping, the sanitary landfill eliminates health hazards and permits reclamation of the site for construction, recreation, or other purposes. The chief drawbacks are that feasible locations are relatively rare and costly and that sites must be insulated from water resources to avoid polluting them (see water pollution). Both open dump and sanitary landfill disposal depend on the natural degradability of wastes for an ultimate return to normal earth conditions. Decay, however, takes time; buried paper, for example, can persist as long as 60 years. Many plastics and synthetic textiles do not degrade at all.
To reduce the bulk of solid waste burning of paper, plastic, and other components is often resorted to, either in open dumps or incinerators. Fly ash, noxious gases, and chemical contaminants can thus be released into the air (see air pollution). However, new techniques for "scrubbing" pollutants from incinerator stacks are being developed. Incineration of typical garbage reduces its weight and volume by as much as 80%. Approximately 15.9% of municipal solid waste is combusted.
Recycling of solid wastes is an option that many municipalities have explored in recent years. It not only facilitates disposal but conserves energy, cuts pollution, and preserves natural resources. To make cans from recovered aluminum, for example, requires 10% of the energy needed to make them from virgin ore. At the same time ore is saved, and the pollution resulting from mining and processing are avoided. Making steel bars from scrap requires 74% less energy and 50% less water, while reducing air-polluting emissions by 85% and mining wastes by 95%.
Similarly, sludge from treated sewage can be used for fertilizer, but it has been less costly to dump it at sea or on open land (see sewerage). Dumped sludge has killed marine life and threatened beaches along the Eastern seaboard; elsewhere in the United States it is a growing nuisance. Between 1975 and 1985 the amount of sludge dumped in U.S. coastal waters increased by 60%; the effects of dumping and illegal dumping are still felt despite the fact that it has been illegal since the beginning of 1992. Recycling and composting take care of approximately 2.7% of municipal solid waste.
The federal government now provides assistance to localities in developing new means of recovering materials and energy from solid waste, and encourages private industry to seek similar goals. One technique being tried involves intensified combustion of wastes to produce heat for generating power. A second promising approach is pyrolysis, the thermal decomposition of wastes in controlled amounts of oxygen to produce valuable petrochemicals; the residue is an inert char of little bulk. Another method of reducing solid wastes is to replace polystyrene packaging with less bulky wrapping made largely of paper. Wider application of such processes is being advocated not only to diminish pollution of the environment by solid waste, but also to conserve natural resources.