Scrubbers are air-pollution-control devices that remove harmful gases and particulates from the smokestacks of incinerators, chemical manufacturing facilities, and electric power plants before they enter the atmosphere. There are different types of scrubbers, including wet and dry, regenerative and nonregenerative. Regenerative scrubbers recycle the material that extracts the pollutants.

The nonregenerative wet scrubber is most commonly used to capture sulfur dioxide emitted from coal and oil burning power plants. It works by spraying limestone and water slurry into the flue gases. Sulfur dioxide reacts with limestone to form gypsum or calcium sulfate. The gypsum sludge is disposed of in landfills or recycled in saleable byproducts such as wallboard, concrete, and fertilizer.

Regenerative scrubbers can also be used; one reacts sodium sulfite with sulfur dioxide to form sodium bisulfite, from which sodium sulfite is recovered by adding alkali. The released sulfur is trapped in water to produce sulfuric acid, which is sold to offset the cost of installing the scrubber.

Particulates can be removed using venturi and centrifugal or condensation scrubbers. Flue gas enters through the top of the cone-shaped venturi scrubber and water, injected horizontally, forms droplets that absorb dust and other particles. The resulting slurry discharges from the bottom of the unit or can be separated from the clean gas by centrifugation or spinning at high speed. Copper oxide regenerable scrubbers that absorb sulfur and simultaneously convert nitrogen oxides to nitrogen are being researched.

In 1971 the EPA set a maximum limit on sulfur dioxide in air. To help meet this limit, revisions to the Clean Air Act in 1977 required all new power plants to install scrubbers to remove sulfur dioxide. Most spray tower scrubbers remove at least 90 percent of sulfur dioxide, according to the EPA.

In 1990 further revisions to the Clean Air Act under the Acid Rain Program allotted allowable amounts of sulfur dioxide emissions to electric utilities, which could trade allowances to meet their quotas. Sulfur dioxide emissions from power plants in 2001 were 33 percent lower than in 1990 and 5 percent lower than in 2000 according to the EPA.


The reuse of products, materials, and parts can have significant environmental and economic benefits. Waste is not just created when consumers throw items away. Waste is generated throughout the life cycle of a product, from extraction of raw materials, to transportation to processing and manufacturing facilities, to manufacture and use.

Reusing items or making them with less material decrease waste dramatically. Ultimately, less material will need to be recycled or sent to landfills or waste-combustion facilities.

Used goods are widely available to industries, businesses, institutions, and individuals. There are secondhand markets for entire industrial production facilities, such as breweries and chemical production plants, as well as for industrial, construction, and medical equipment.

Used goods for individuals include cars, clothes, books, furniture, household items, sports equipment, and musical instruments. Sources of used goods include on-line auctions and markets, secondhand merchandise stores, classified advertisements, estate sales, auctions, rummage sales, yard sales, salvage yards, materials exchanges, trash salvaging or “dumpster diving.”

Amount of Reuse

In the United States, several secondhand markets are $100 billion dollar industries, and several more fall in the $1 to $10 billion range. Each year 40 million used cars are sold in the United States, nearly three times the number of new cars purchased.

Overall, secondhand markets are almost as large as consumer recycling in terms of the amount of material processed (approximately fifty million tons of paper and ten million tons of glass are recycled annually in the United States), and the economic value of secondhand markets is far greater than those for recycling.

A considerable percentage of secondhand goods are exported from the United States, especially clothing; automobiles; and industrial, construction, and medical equipment. In a number of countries, including the Czech Republic, Nigeria, Uganda, and Zimbabwe, imports of used clothing compete strongly with the domestic production of new clothes.

Theory of Reuse

Reuse can reduce the pollution and resource use associated with manufacturing a new item, and can delay or eliminate disposal of the item. In order to experience the greatest environmental benefits, reuse of an item needs to replace, at least partially, the purchase and production of a new item.

In some situations, reuse may not incur any real benefits. For example, if a car owner sells or gives a car to someone who would not otherwise possess a car, and then buys a new car to replace the old one, the result is that there are now two operating cars rather than one. In other situations, the reuse of an item may have zero effect on the production or purchase of new items.

For example, if someone buys a “white elephant” at a rummage sale (perhaps a necklace or a used compact disc), that purchase will not in any way prevent or replace the purchase of a new item. However, even if reuse has no tangible environmental benefits, it can have economic and social welfare benefits.

If the car example above is reconsidered, for instance, two people, not just one, now own a useful vehicle. In the compact disc example, the buyer acquires another disc for his or her pleasure, and the seller earns some perhaps much needed cash.

Reuse can replace the production and purchase of new items, especially when the first owner does not sell in order to be able to buy a new item. Examples of this sort include clothes and furniture, which are typically given away or sold at low prices by the first owners, and which second-hand buyers often buy instead of new items.

Role of Government and Industry

The U.S. government is one of the largest purveyors of used goods in the United States; it regularly sells surplus items through sealed bids, auctions, silent auctions, and fixed-price sales. On the other hand, government regulations largely prevent the purchase of used items by the U.S. government and require the labeling of products containing used parts in a way that may discourage the use of used parts by industry.

There are both incentives and disincentives for reuse by industry. Reuse, remanufacturing, repair, and refurbishment of products and parts can be economically beneficial for industry. For example, used copiers are often remanufactured and refurbished. A number of companies now sell modular, reusable carpet. On the other hand, firms in some cases have an incentive to discourage reuse of their products, in order to maintain and increase production of new goods.

Reuse by the Individual

Individuals can maximize the environmental and economic benefits of their own reuse efforts by carefully contemplating their reuse strategies, by developing the ability to make repairs, and by learning about local sources of used goods and replacement parts. The environmental and economic benefits of reuse typically increase as the size and cost of the item increase. For example, new furniture is both resource-intensive and expensive.

Repair, repainting, and reupholstering of used furniture can replace the purchase of new furniture. The regular repair of shoes can considerably extend their life. Used clothing, ranging from designer clothes at consignment stores to basic items at rummage sales, is widely available.

Used books, sports equipment, and musical instruments are also available at local stores and on-line. Used building materials (doors, windows, hardware, etc.) are increasingly available at salvage yards such as Urban Ore in Berkeley, California.

Reuse can have significant environmental and economic benefits by replacing the purchase of a new item. Secondhand items range from large industrial facilities and equipment to cars, sports equipment, clothes, and toys for individuals. Businesses can benefit from secondhand markets both by buying secondhand equipment and by selling surplus equipment for reuse.

Individuals can make a valuable contribution to the environment and their own finances by learning to make repairs, by wisely shopping for secondhand goods, and by selling or donating their unwanted goods so that others may use them.


Sediments in the aquatic ecosystem are analogous to soil in the terrestrial ecosystem as they are the source of substrate nutrients, and micro- and macroflora and -fauna that are the basis of support to living aquatic resources.

Sediments are the key catalysts of environmental food cycles and the dynamics of water quality. Aquatic sediments are derived from and composed of natural physical, chemical, and biological components generally related to their watersheds.

Sediments range in particle distribution from micron-sized clay particles through silt, sand, gravel, rock, and boulders. Sediments originate from bed load transport, beach and bank erosion, and land runoff. They are naturally sorted by size through prevalent hydrodynamic conditions.

In general, fast-moving water will contain coarse-grained sediments and quiescent water will contain fine-grained sediments. Mineralogical characteristics of sediments vary widely and reflect watershed characteristics. Organic material in sediments is derived from the decomposed tissues of plants and animals, from aquatic and terrestrial sources, and from various point and nonpoint wastewater discharges.

The content of organic matter increases in concentration as the size of sediment mineral particles decreases. Dissolved chemicals in the overlying and sediment pore waters are a product of inorganic and organic sedimentary materials, as well as runoff and ground water that range from fresh to marine in salinity.

This sediment/water environment varies significantly over space and time and its characteristics are driven by complex biogeochemical interaction between the inorganic, living, and nonliving organic components. The sediment biotic community includes micro-, meso-, and macrofauna and -flora that are interdependent of each other and their host sediment’s biogeochemical characteristics.

Sedimentation is the direct result of the loss (erosion) of sediments from other aquatic areas or land-based areas. Sedimentation can be detrimental or beneficial to aquatic environments. Moreover, sediment impoverishment (erosion or lack of replenishment) in an area can be as bad as too much sedimentation. Sedimentation in one area is linked to erosion or impoverishment in another area and is a natural process of all water bodies (i.e., lakes, rivers, estuaries, coastal zones, and even the deep ocean).

As an example, detrimental effects can be related to the burial of bottom-dwelling organisms and beneficial effects can be related to the building of new substrates for the development of marshes. These natural physical processes will continue whether or not they are influenced by the activities of humankind.

Human activities, however, have significantly enhanced sedimentation as well as sediment loss. Sedimentation activities can be land-based (i.e., agriculture, forestry, construction, urbanization, recreation) and water-based (i.e., dams, navigation, port activities, drag fishing, channelization, water diversions, wetlands loss, other large-scale hydrological modifications). Sediment impoverishment or loss is generally due to retention behind dams, bank or beach protection activities, water diversions, and many of the aquatic activities cited here.

Morphological changes (physical changes over a large area) to large aquatic systems can also result in major changes in natural sediment erosion and sedimentation patterns. As an example, the change in the size and shape of a water body will result in new water flow patterns leading to erosion or sediment removal from sensitive areas.

The environmental impacts of sedimentation include the following: loss of important or sensitive aquatic habitat, decrease in fishery resources, loss of recreation attributes, loss of coral reef communities, human health concerns, changes in fish migration, increases in erosion, loss of wetlands, nutrient balance changes, circulation changes, increases in turbidity, loss of submerged vegetation, and coastline alteration.

Abatement or control of sedimentation can be successful if implemented on a broad land area or watershed scale and is directly related to improvement in land-use practices. Agriculture and forestry (logging) improvements where soil loss is minimized are not only technically feasible: They can be carried out at a moderate cost and with net benefits.

The U.S. Department of Agriculture has a wide range of training and implementation programs for these types of activities. The United Nations Environmental Programme also has global programs, their Regional Seas activities, to guide countries in the management of land-based activities negatively impacting the coastal zone.

Improved land-use practices are the primary measures to control sediment sources: terracing, low tillage, modified cropping, reduced agricultural intensity (e.g., no-till buffer zones), and wetlands construction as sediment interceptors. Forestry practices such as clear-cutting to the water’s edge without replacement tree planting must be seriously curtailed because base soil in exposed areas will erode and import sediment to sensitive aqueous areas.

Wetlands that separate upland areas from aquatic areas serve as natural filters for the runoff from the adjacent land. Wetlands thus serve to trap soil particles and associated agricultural contaminants. The construction of natural buffer zones and wetlands replenishment adjacent to logging areas are effective techniques.

Watershed construction activities such as port expansion, water diversions, channel deepening, and new channel construction must undergo a complete environmental assessment, coupled with predictive sediment resuspension and transport modeling, so alternative courses of action and activities to minimize the negative impacts of sedimentation may be chosen.

Sediment impoverishment is equally important in coastal areas, such as coastal Louisiana where twenty-five to thirty square miles of wetlands are being lost each year. This loss primarily results from the Mississippi River levee system halting the annual natural replenishment of sediments that rebuilds the marsh system.

Engineered water diversion can replace sediment in the natural system to decrease losses due to dams, levees, jetties, and other structures built to control the flow of water and thus sediments. Proper placement of sediments from navigation dredging can also be a useful abatement technique.

Sediments are absolutely necessary for aquatic plant and animal life. Managed properly, sediments are a resource; improper sediment management results in the destruction of aquatic habitat that would have otherwise depended on their presence.

The United Nations Group of Experts on the Scientific Aspects of Marine Environmental Protection recently recognized that on a global basis, changes in sediment flows are one of the five most serious problems affecting the quality and uses of the marine and coastal environment.


Mined ores are processed to concentrate the minerals of interest. In the case of metal ores, these mineral concentrates usually need to be further processed to separate the metal from other elements in the ore minerals.

Smelting is the process of separating the metal from impurities by heating the concentrate to a high temperature to cause the metal to melt. Smelting the concentrate produces a metal or a high-grade metallic mixture along with a solid waste product called slag.

The principal sources of pollution caused by smelting are contaminantladen air emissions and process wastes such as wastewater and slag.

One type of pollution attributed to air emissions is acid rain. The smelting of sulfide ores results in the emission of sulfur dioxide gas, which reacts chemically in the atmosphere to form a sulfuric acid mist. As this acid rain falls to the earth, it increases the acidity of soils, streams, and lakes, harming the health of vegetation and fish and wildlife populations.

In older smelters, air emissions contained elevated levels of various metals. Copper and selenium, for example, which can be released from copper smelters, are essential to organisms as trace elements, but they are toxic if they are overabundant.

These metals can contaminate the soil in the vicinity of smelters, destroying much of the vegetation. In addition, particulate matter emitted from smelters may include oxides of such toxic metals as arsenic (cumulative poison), cadmium (heart disease), and mercury (nerve damage).

When compared to pollution caused by air emissions, process wastes and slag are of less concern. In modern smelters, much of the wastewater generated is returned to the process. If the economic value of the metal concentrate in slag is high enough, the slag may be returned to the process, thereby reducing the amount requiring permanent disposal.

New technologies are playing an important role in reducing or even preventing smelter pollution. Older smelters emitted most of the sulfur dioxide generated, and now almost all of it is captured prior to emission using new technologies, such as electrostatic precipitators, which capture dust particles and return them to the process. Raw material substitution or elimination, such as recycling lead batteries and aluminum cans, decreases the need to process ore, which reduces pollution.

Some of the major federal statutes and regulations that apply to smelting are the same as those that have applied to mining since the Clean Air Act (CAA) of 1970 became law. The CAA established nationally uniform standards that control particular hazardous air pollutants.

Sudbury, in Ontario, Canada, is one of the world’s largest smelting complexes, with an international reputation as a highly polluted area that has been mined for more than one hundred years. The environmental impact was completely or partially denuded vegetation on over 46,000 hectares and 7,000 acid-damaged lakes.

Smelting caused much of the ecological damage via acid rain and elevated levels of copper and nickel in the vicinity of the smelters. Efforts by government and industry since the 1970s have eliminated most of the sulfur dioxide emissions in the area, and there has been significant progress toward achieving sustainable ecosystems.


Originally, the term smog was coined to describe the mixture of smoke and fog that lowered visibility and led to respiratory problems in industrial cities. More recently, the term has come to mean any decrease in air quality whether associated with reduced visibility or a noticeable impact on human health.

Smog occurs when emissions of gases and particles from industrial or transportation sources are trapped by the local meteorology so the concentrations rise and chemical reactions occur. It is common to distinguish between two types of smog: London smog and Los Angeles smog.

London, or sulphurous, smog was noted following the introduction of coal into cities. It is most prevalent in the fall or winter when cool conditions naturally produce a thick surface fog. This fog mixes with the smoke and gases from burning coal to produce a dark, thick, acrid sulphurous atmosphere.

Normally, the unpolluted fog would disperse during the day and be reformed at night. However, the presence of smoke particles makes the fog so thick that sunlight cannot penetrate it and so only a major change in meteorology can disperse it. The smog has been shown to contribute to an increased death rate, primarily due to respiratory problems.

The most notable example of this kind of smog occurred in London, from December 4 to 10, 1954, when some four thousand deaths in excess of normal averages resulted. A similar episode in Donora, Pennsylvania, in 1948 involved approximately twenty excess deaths. Most jurisdictions have instituted control measures to prevent this level of disaster from happening again.

They have moved industries out of cities, demanded lower industrial emissions, and increased the heights of smokestacks so emissions are not trapped by local meteorology. These approaches have been largely successful, at least in controlling the most extreme events.

Los Angeles, or photochemical, smog first became apparent in the late 1940s in warm sunny cities that did not have significant coal-burning industries. It is a daytime phenomenon characterized by a white haze and contains oxidants, such as ozone, that cause eyes to water, breathing to become labored, and plants to be damaged.

It results from the action of sunlight on the combination of hydrocarbons and nitrogen oxides (NOx), known as precursor gases. These are emitted from combustion sources to produce a range of oxidized products and oxidants.

These compounds have been shown to produce respiratory and cardiac problems in individuals sensitive to pollution, and the damage inflicted on crops can cause significant decreases in yield. In most cities, the automobile is the primary contributor of smog’s precursor gases.

As the name would suggest, the most notable example of this type of smog occurs in Los Angeles, California, but it has also been experienced in a large number of cities where the weather is dry, sunlight is plentiful, and there are many automobiles or petroleum industries (e.g., Houston, Athens, and Mexico City.)

The control of photochemical smog is more difficult than for sulphurous smog because the compounds responsible for human and crop impacts are not directly emitted, but produced by chemistry in the atmosphere. Thus, greater knowledge on the emissions of gases, their reactions in the atmosphere, and their lifetime is needed. Most jurisdictions continue to focus their control strategies on reducing ozone concentrations, although particle concentrations are receiving increasing attention.

Because smog results from the sunlight-initiated chemistry of hydrocarbons and nitrous oxides, the most common approach to smog control is to decrease the emission of these compounds at their source. Lower volatility gasolines and systems to capture gasoline vapors are used to reduce hydrocarbon emissions while tailpipe controls (catalytic converters) reduce emissions of both hydrocarbons and nitrogen oxides.

The emission control systems of the twenty-first century mean that a car typically emits 70 percent less nitrogen oxides and 80 to 90 percent less hydrocarbons than the uncontrolled cars of the 1960s. The expected improvement in air quality, as a result of increasing controls, is estimated by using computer models of the atmosphere and its chemistry.

Soil Pollution

Soil pollution comprises the pollution of soils with materials, mostly chemicals, that are out of place or are present at concentrations higher than normal which may have adverse effects on humans or other organisms.

It is difficult to define soil pollution exactly because different opinions exist on how to characterize a pollutant; while some consider the use of pesticides acceptable if their effect does not exceed the intended result, others do not consider any use of pesticides or even chemical fertilizers acceptable.

However, soil pollution is also caused by means other than the direct addition of xenobiotic (man-made) chemicals such as agricultural runoff waters, industrial waste materials, acidic precipitates, and radioactive fallout.

Both organic (those that contain carbon) and inorganic (those that don’t) contaminants are important in soil. The most prominent chemical groups of organic contaminants are fuel hydrocarbons, polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated aromatic compounds, detergents, and pesticides.

Inorganic species include nitrates, phosphates, and heavy metals such as cadmium, chromium and lead; inorganic acids; and radionuclides (radioactive substances). Among the sources of these contaminants are agricultural runoffs, acidic precipitates, industrial waste materials, and radioactive fallout.

Soil pollution can lead to water pollution if toxic chemicals leach into groundwater, or if contaminated runoff reaches streams, lakes, or oceans. Soil also naturally contributes to air pollution by releasing volatile compounds into the atmosphere. Nitrogen escapes through ammonia volatilization and denitrification. The decomposition of organic materials in soil can release sulfur dioxide and other sulfur compounds, causing acid rain.

Heavy metals and other potentially toxic elements are the most serious soil pollutants in sewage. Sewage sludge contains heavy metals and, if applied repeatedly or in large amounts, the treated soil may accumulate heavy metals and consequently become unable to even support plant life.

In addition, chemicals that are not water soluble contaminate plants that grow on polluted soils, and they also tend to accumulate increasingly toward the top of the food chain.

The banning of the pesticide DDT in the United States resulted from its tendency to become more and more concentrated as it moved from soil to worms or fish, and then to birds and their eggs. This occurred as creatures higher on the food chain ingested animals that were already contaminated with the pesticide from eating plants and other lower animals.

Lake Michigan, as an example, has 2 parts per trillion (ppt) of DDT in the water, 14 parts per billion (ppb) in the bottom mud, 410 ppb in amphipods (tiny water fleas and similar creatures), 3 to 6 parts per million (ppm) in fish such as coho salmon and lake trout, and as much as 99 ppm in herring gulls at the top of the food chain.

The ever-increasing pollution of the environment has been one of the greatest concerns for science and the general public in the last fifty years. The rapid industrialization of agriculture, expansion of the chemical industry, and the need to generate cheap forms of energy has caused the continuous release of man-made organic chemicals into natural ecosystems. Consequently, the atmosphere, bodies of water, and many soil environments have become polluted by a large variety of toxic compounds.

Many of these compounds at high concentrations or following prolonged exposure have the potential to produce adverse effects in humans and other organisms: These include the danger of acute toxicity, mutagenesis (genetic changes), carcinogenesis, and teratogenesis (birth defects) for humans and other organisms. Some of these man-made toxic compounds are also resistant to physical, chemical, or biological degradation and thus represent an environmental burden of considerable magnitude.

Numerous attempts are being made to decontaminate polluted soils, including an array of both in situ (on-site, in the soil) and off-site (removal of contaminated soil for treatment) techniques. None of these is ideal for remediating contaminated soils, and often, more than one of the techniques may be necessary to optimize the cleanup effort.

The most common decontamination method for polluted soils is to remove the soil and deposit it in landfills or to incinerate it. These methods, however, often exchange one problem for another: landfilling merely confines the polluted soil while doing little to decontaminate it, and incineration removes toxic organic chemicals from the soil, but subsequently releases them into the air, in the process causing air pollution.

For the removal and recovery of heavy metals various soil washing techniques have been developed including physical methods, such as attrition scrubbing and wet-screening, and chemical methods consisting of treatments with organic and inorganic acids, bases, salts and chelating agents.

For example, chemicals used to extract radionuclides and toxic metals include hydrochloric, nitric, phosphoric and citric acids, sodium carbonate and sodium hydroxide and the chelating agents EDTA and DTPA. The problem with these methods, however, is again that they generate secondary waste products that may require additional hazardous waste treatments.

In contrast to the previously described methods, in situ methods are used directly at the contamination site. In this case, soil does not need to be excavated, and therefore the chance of causing further environmental harm is minimized. In situ biodegradation involves the enhancement of naturally occurring microorganisms by artificially stimulating their numbers and activity. The microorganisms then assist in degrading the soil contaminants.

A number of environmental, chemical, and management factors affect the biodegradation of soil pollutants, including moisture content, pH, temperature, the microbial community that is present, and the availability of nutrients. Biodegradation is facilitated by aerobic soil conditions and soil pH in the neutral range (between pH 5.5 to 8.0), with an optimum reading occurring at approximately pH 7, and a temperature in the range of 20 to 30°C.

These physical parameters can be influenced, thereby promoting the microorganisms’ ability to degrade chemical contaminants. Of all the econtamination methods bioremediation appears to be the least damaging and most environmentally acceptable technique.

Space Pollution

In the most general sense, the term space pollution includes both the natural micrometeoroid and man-made orbital debris components of the space environment; however, as “pollution” is generally considered to indicate a despoiling of the natural environment, space pollution here refers to only man-made orbital debris. Orbital debris poses a threat to both manned and unmanned spacecraft as well as the earth’s inhabitants.

Environmental and Health Impacts

The effects of debris on other spacecraft range from surface abrasion due to repeated small-particle impact to a catastrophic fragmentation due to a collision with a large object. The relative velocities of orbital objects (10 kilometers per second [km/s] on average, but ranging from meters per second up to 15.5 km/s) allow even very small objects—such as a paint flake—to damage spacecraft components and surfaces.

For example, a 3-millimeter (mm) aluminum particle traveling at 10 km/s is equivalent in energy to a bowling ball traveling at 60 miles per hour (or 27 m/s). In this case, all the energy would be distributed in an area of the same size as the particle, causing cratering or penetration, depending on the thickness and material properties of the surface being impacted.

There has been one accidental collision between cataloged objects to date, but surfaces returned from space and examined in the laboratory confirm a regular bombardment by small particles. Space Shuttle vehicle components, including windows, are regularly replaced due to such damage acquired while in orbit. Debris also poses a hazard to the surface of the Earth.

High-melting-point materials such as titanium, steel, ceramics, or large or densely constructed objects can survive atmospheric reentry to strike the earth’s surface. Although there have been no recorded fatalities or severe injuries due to debris, reentering objects are regularly observed and occasionally found.

Debris is typically divided into three size ranges, based on the damage it may cause: less than 1 centimeter (cm), 1 to 10 cm, and larger than 10 cm. Objects less than 1 cm may be shielded against, but they still have the potential to damage most satellites. Debris in the 1 to 10 cm is not shielded against, cannot easily be observed, and could destroy a satellite.

Finally, collisions with objects larger than 10 cm can break up a satellite. Of these size ranges, only objects 10 cm and larger are regularly tracked and cataloged by surveillance networks in the United States and the former Soviet Union.

The other populations are estimated statistically through the analysis of returned surfaces (sizes less than 1 mm) or special measurement campaigns with sensitive radars (sizes larger than 3 mm). Estimates for the populations are approximately 30 million debris between 1 mm and 1 cm, over 100,000 debris between 1 and 10 cm, and 8,800 objects larger than 10 cm.

The number, nature, and location of objects greater than 10 cm in size are provided in the fragmentation debris table and in the image of space debris around Earth. Low Earth orbit (LEO) is defined as orbital altitudes below 2,000 km above the earth’s surface and is the subject of the image of space debris around Earth.

Middle Earth orbit (MEO) is the province of the Global Positioning System (GPS) and Russian navigation satellite systems and is located at approximately 20,000-km altitude, whereas the geosynchronous Earth orbit (GEO) “belt” is inhabited primarily by communications and Earth—observation payloads around 35,800 km. The majority of objects in these orbital regions are in circular or near-circular orbits about the earth.

In contrast, the elliptical orbit category includes rocket bodies left in their transfer (payload delivery) orbits to MEO and GEO as well as scientific, communications, and Earth-observation payloads. Of all objects listed in the fragmentation debris table, the vast majority are “debris”—only about 5 percent of objects in orbit represent operational payloads or spacecraft.

Also, of the approximately 28,000 objects that have been tracked, beginning with the launch of Sputnik 1 in October 1957, those not accounted for in the fragmentation debris table have either reentered the earth’s atmosphere or have escaped the earth’s influence (to land on Mars, for example). The distribution of debris smaller than 10 cm is predicated on the orbits of the parent objects and is assumed to be very similar to the distributions presented in the image of space debris around Earth.

Remediation Strategies

Remediation takes two courses: protection and mitigation. Protection seeks to shield spacecraft and utilize intelligent design practices to minimize the effects of debris impact. Mitigation attempts to prevent debris from being created. Active mitigation techniques include collision avoidance between tracked and maneuverable objects and the intentional reentry of objects over the oceans.

Passive techniques include venting residual fuels or pressurized vessels aboard rockets and spacecraft, retaining operational debris, and placing spacecraft into disposal orbits at the end of a mission. Space salvage or retrieval, while an option, is currently too expensive to employ on a regular basis.

The United States and international space agencies recognize the threat of debris and are cooperating to limit its environmental and health hazards. The Interagency Space Debris Coordination Committee (IADC), sponsored originally by the National Aeronautics and Space Administration (NASA), has grown to include all major space-faring nations.

The IADC charter includes the coordination and dissemination of remediation research, and strategies based on research results are being adopted by the worldwide space community.

Remediation strategies have resulted in a decline in the rate of debris growth in the 1990s although the overall population continues to grow. Continued work is necessary, however, to reduce the orbital debris hazard for future generations and continue the safe, economical utilization of space.

Sustainable Development

The term sustainable development gained international recognition after the World Commission on Environment and Development (the Brundtland Commission) released its report Our Common Future in 1983.

In this report, sustainable development was defined as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”

The International Union for Conservation of Nature and Natural Resources had introduced the term earlier in its 1980 publication World Conservation Strategy, stating, “Development and conservation operate in the same global context, and the underlying problems that must be overcome if either is to be successful are identical.” It thus recommended a strategy entitled, “Towards Sustainable Development.”

Development refers to any systematic progress toward some improved or advanced condition. In the international development field, in which the term sustainable development is most often encountered, development refers to the establishment of the physical and social conditions that make economic progress possible.

In the past this has at times involved the transformation of forests, wetlands, soil, and other resources in ways that ultimately undermined the capacity of the natural environment to produce conditions able to sustain future advances in the quality of people’s lives. The concept of sustainable development thus suggests an alternative strategy in which economic progress and environmental protection go hand in hand.

The negative environmental impacts of some forms of economic development had been recognized long before the term sustainable development was popularized in the 1980s. The earliest settled communities subjected the harvesting of important food and raw materials to rules, customs, and eventually formal laws and regulations designed to protect renewable resources for the future.

In his book Man and Nature published in 1867, George Perkins Marsh drew attention to the environmental changes he had witnessed in both the United States and the Mediterranean region. His alarm was echoed by early American conservationists Gifford Pinchot and John Muir at the beginning of the twentieth century and again by Rachel Carson in her 1962 book Silent Spring.

Then in 1972 an environmentally aware group of industrialists known as the Club of Rome issued a report, The Limits to Growth, that warned of inadequate natural resource supplies and disruption to global ecosystems if population and economic growth were to continue on their current path.

In 1971 the International Institute for Environment and Development (IIED) was established in Britain with a mandate to seek ways to achieve economic progress without destroying the environmental resource base.

In June 1992 the United Nations Conference on Environment and Development (UNCED) further refined the term by developing an agenda for nations to follow that would move the world toward sustainable development. Agenda 21, as it was called, was a three-hundred-page plan for achieving sustainable development in the twenty-first century.

To assist in follow up and monitor the progress of Agenda 21, and to report on the implementation of related agreements, the United Nations created the Commission on Sustainable Development (CSD), to report to the UN Economic and Social Council (ECOSO).

Although the concept of sustainable development has received considerable attention in international diplomatic and policy circles, it does have its critics. Many claim sustainable development is an oxymoron. They argue that nothing, least of all economic development, is sustainable forever.

For them, the concept of sustainable development is wishful thinking that distracts nations from the necessary transformations of the global economy. Others claim that a determined focus on sustainability is likely to lead to economic stagnation and continued underdevelopment.

The proponents of sustainable development believe that the current mode of economic development is fundamentally destructive and must be radically reformed, and although nothing is absolutely sustainable, the effort to hold development activities accountable for the environmental conditions they produce makes both long-term economic and ethical sense.

They argue that this approach, when combined with efforts to reduce population growth rates, reduce consumption among the richest nations of the world, promote the substitution of renewable for nonrenewable natural resources, reduce waste from manufacturing processes, and improve efficiency in the use of materials, is the only approach that offers a positive future outlook for the welfare of the global community.

In the decade since Agenda 21 was accepted as a strategy for sustainable development, progress has been made. International agreements have been promulgated that will have a positive effect on sustainable development. These include, among others, the efforts of the United Nations in formulating a framework convention on climate change, a convention on biological diversity and a global compact that combines concerns for human rights, labor, and the environment.

In addition, standards for business activity that consider environmental consequences have been agreed to by the International Organization for Standardization (ISO 14000), and the international business community has created the World Business Council for Sustainable Development. The World Bank has applied the concept of sustainable development with its reformed lending practices requiring recipients to demonstrate sound environmental criteria.

Cities around the world are adopting sustainable criteria for land-use planning and zoning, and individuals are making personal consumption choices with sustainable development in mind. Though the problems of a sustainable future are far from solved, there is much about which to be optimistic.

Thermal Pollution

The broadest definition of thermal pollution is the degradation of water quality by any process that changes ambient water temperature. Thermal pollution is usually associated with increases of water temperatures in a stream, lake, or ocean due to the discharge of heated water from industrial processes, such as the generation of electricity.

Increases in ambient water temperature also occur in streams where shading vegetation along the banks is removed or where sediments have made the water more turbid.

Both of these effects allow more energy from the sun to be absorbed by the water and thereby increase its temperature. There are also situations in which the effects of colder-than-normal water temperatures may be observed. For example, the discharge of cold bottom water from deep-water reservoirs behind large dams has changed the downstream biological communities in systems such as the Colorado River.

Vehicular Pollution

The large majority of today’s cars and trucks travel by using internal combustion engines that burn gasoline or other fossil fuels. The process of burning gasoline to power cars and trucks contributes to air pollution by releasing a variety of emissions into the atmosphere.

Emissions that are released directly into the atmosphere from the tailpipes of cars and trucks are the primary source of vehicular pollution. But motor vehicles also pollute the air during the processes of manufacturing, refueling, and from the emissions associated with oil refining and distribution of the fuel they burn.

Primary pollution from motor vehicles is pollution that is emitted directly into the atmosphere, whereas secondary pollution results from chemical reactions between pollutants after they have been released into the air.

Despite decades of efforts to control air pollution, at least 92 million Americans still live in areas with chronic smog problems. The U.S. Environmental Protection Agency (EPA) predicts that by 2010, even with the benefit of current and anticipated pollution control programs, more than 93 million people will live in areas that violate health standards for ozone (urban smog), and more than 55 million Americans will suffer from unhealthy levels of fine-particle pollution, which is especially harmful to children and senior citizens.

While new cars and light trucks emit about 90 percent fewer pollutants than they did three decades ago, total annual vehicle-miles driven have increased by more than 140 percent since 1970 and are expected to increase another 25 percent by 2010.

The emission reductions from individual vehicles have not adequately kept pace with the increase in miles driven and the market trend toward more-polluting light trucks, a category that includes sports utility vehicles (SUVs). As a result, cars and light trucks are still the largest single source of air pollution in most urban areas, accounting for one-quarter of emissions of smog-forming pollutants nationwide.

Ingredients of Vehicular Pollution

The following are the major pollutants associated with motor vehicles:
  • Ozone (O3). The primary ingredient in urban smog, ozone is created when hydrocarbons and nitrogen oxides (NOx)—both of which are chemicals released by automobile fuel combustion—react with sunlight. Though beneficial in the upper atmosphere, at the ground level ozone can irritate the respiratory system, causing coughing, choking, and reduced lung capacity.
  • Particulate matter (PM). These particles of soot, metals, and pollen give smog its murky color. Among vehicular pollution, fine particles (those less than one-tenth the diameter of a human hair) pose the most serious threat to human health by penetrating deep into lungs. In addition to direct emissions of fine particles, automobiles release nitrogen oxides, hydrocarbons, and sulfur dioxide, which generate additional fine particles as secondary pollution.
  • Nitrogen oxides (NOx). These vehicular pollutants can cause lung irritation and weaken the body’s defenses against respiratory infections such as pneumonia and influenza. In addition, they assist in the formation of ozone and particulate matter. In many cities, NOx pollution accounts for one-third of the fine particulate pollution in the air.
  • Carbon monoxide (CO). This odorless, colorless gas is formed by the combustion of fossil fuels such as gasoline. Cars and trucks are the source of nearly two-thirds of this pollutant. When inhaled, CO blocks the transport of oxygen to the brain, heart, and other vital organs in the human body. Newborn children and people with chronic illnesses are especially susceptible to the effects of CO.
  • Sulfur dioxide (SO2). Motor vehicles create this pollutant by burning sulfur-containing fuels, especially diesel. It can react in the atmosphere to form fine particles and can pose a health risk to young children and asthmatics.
  • Hazardous air pollutants (toxics). These chemical compounds, which are emitted by cars, trucks, refineries, gas pumps, and related sources, have been linked to birth defects, cancer, and other serious illnesses. The EPA estimates that the air toxics emitted from cars and trucks account for half of all cancers caused by air pollution

Vehicular Emissions That Contribute to Global Warming

Carbon monoxide, ozone, particulate matter, and the other forms of pollution listed above can cause smog and other air quality concerns, but there are vehicular emissions that contribute to a completely different pollution issue: global warming.

The gases that contribute to global warming are related to the chemical composition of the Earth’s atmosphere. Some of the gases in the atmosphere function like the panes of a greenhouse. They let some radiation (heat) in from the sun but do not let it all back out, thereby helping to keep the Earth warm.

The past century has seen a dramatic increase in the atmospheric concentration of heat-trapping gasses, due to human activity. If this trend continues, scientists project that the earth’s average surface temperature will increase between 2.5°F and 10.4°F by the year 2100.

One of these important heat-trapping gasses is carbon dioxide (CO2). Motor vehicles are responsible for almost one-quarter of annual U.S. emissions of CO2. The U.S. transportation sector emits more CO2 than all but three other countries’ emissions from all sources combined.

Curbing Vehicular Pollution

Vehicular emissions that contribute to air quality problems, smog, and global warming can be reduced by putting better pollution-control technologies on cars and trucks, burning less fuel, switching to cleaner fuels, using technologies that reduce or eliminate emissions, and reducing the number of vehiclemiles traveled.

Pollution Control Technology

Federal and California regulations require the use of technologies that have dramatically reduced the amount of smog-forming pollution and carbon monoxide coming from a vehicle’s tailpipe. For gasoline vehicles, “threeway” catalysts, precise engine and fuel controls, and evaporative emission controls have been quite successful. More advanced versions of these technologies are in some cars and can reduce smog-forming emissions from new vehicles by a factor of ten. For diesel vehicles, “two-way” catalysts and engine controls have been able to reduce hydrocarbon and carbon monoxide emissions, but nitrogen oxide and toxic particulate-matter emissions remain very high. More advanced diesel-control technologies are under development, but it is unlikely that they will be able to clean up diesel to the degree already achieved in the cleanest gasoline vehicles.

Added concerns surround the difference between new vehicle emissions and the emissions of a car or truck over a lifetime of actual use. Vehicles with good emission-control technology that is not properly maintained can become “gross polluters” that are responsible for a significant amount of existing air-quality problems. New technologies have also been developed to identify emission-equipment control failures, and can be used to help reduce the “gross polluter” problem.

Burning Less Fuel

The key to burning less fuel is making cars and trucks more efficient and putting that efficiency to work in improving fuel economy. The U.S. federal government sets a fuel-economy standard for all passenger vehicles. However, these standards have remained mostly constant for the past decade. In addition, sales of lower-fuel-economy light trucks, such as SUVs, pickups, and minivans, have increased dramatically. As a result, on average, the U.S. passenger-vehicle fleet actually travels less distance on a gallon of gas than it did twenty years ago. This has led to an increase in heat-trapping gas emissions from cars and trucks and to an increase in smog-forming and toxic emissions resulting from the production and transportation of gasoline to the fuel pump.

This trend can be reversed through the use of existing technologies that help cars and trucks go farther on a gallon of gasoline. These include more efficient engines and transmissions, improved aerodynamics, better tires, and high strength steel and aluminum.

More advanced technologies, such as hybrid-electric vehicles that use a gasoline engine and an electric motor plus a battery, can cut fuel use even further. These technologies carry with them additional costs, but pay for themselves through savings at the gasoline pump.

Zero-Emission Vehicles

As more cars and trucks are sold and total annual mileage increases, improving pollution-control technology and burning less fuel continues to be vital, especially in rapidly growing urban areas. However, eliminating emissions from the tailpipe goes even further to cut down on harmful air pollutants.

Hydrogen fuel-cell and electric vehicles move away from burning fuel and use electrochemical processes instead to produce the needed energy to drive a car down the road. Fuel-cell vehicles run on electricity that is produced directly from the reaction of hydrogen and oxygen. The only by product is water—which is why fuel-cell cars and trucks are called zero-emission vehicles. Electric vehicles store energy in an onboard battery, emitting nothing from the tailpipe.

The hydrogen for the fuel cell and the electricity for the battery must still be produced somewhere, so there will still be upstream emissions associated with these vehicles. These stationary sources, however, are easier to control and can ultimately be converted to use wind, solar, and other renewable energy sources to come as close as possible to true zero-emission vehicles.

Cleaner Fuels

The gasoline and diesel fuel in use today contains significant amounts of sulfur and other compounds that make it harder for existing control technology to keep vehicles clean. Removing the sulfur from the fuel and cutting down on the amount of light hydrocarbons helps pollution-control technology to work better and cuts down on evaporative and refueling emissions.

Further large-scale reductions of other tailpipe pollution and CO2 can be accomplished with a shift away from conventional fuels. Alternative fuels such as natural gas, methanol, ethanol, and hydrogen can deliver benefits to the environment while helping to move the United States away from its dependence on oil.

All of these fuels inherently burn cleaner than diesel and gasoline, and they have a lower carbon content - resulting in less CO2. Most of these fuels are also more easily made from renewable resources, and fuels such as natural gas and methanol help provide a bridge to producing hydrogen for fuel-cell vehicles.

Transportation of Waste

The transportation of waste is the movement of waste over a specific area by trains, tankers, trucks, barges, or other vehicles. The types of wastes that may be transported range from municipal garbage to radioactive or hazardous wastes.

Hazardous wastes may be transported to be treated, stored, or disposed of. Facilities that generate hazardous waste are required to prepare a shipping document, or “manifest,” to accompany the waste as it is transported from the site of generation. This manifest must accompany the waste until its final destination and is used to track the wastes from cradle-to-grave.

The potential for pollution releases during the transportation of waste varies; the more hazardous the waste and the larger the volume that is transported, the more devastating the environmental/human health impact if an accident occurs. Traffic accidents or train wrecks can result in waste spills and releases of pollutants that may contaminate the air, water, and soil. Wastes may also be released while being loaded or unloaded during transportation.

Approximately four billion tons of regulated hazardous materials are shipped within the United States each year with more 250,000 shipments entering the U.S. transportation system daily. The Emergency Response Notification System (ERNS) database of the Environmental Protection Agency (EPA) shows that from 1988 to 1992 an average of nineteen transportation accidents involving toxic chemicals occurred each day.

DOT Regulations

The U.S. Department of Transportation (DOT) requires that placards identifying the type of hazardous material being transported be placed on the outside of any vehicle transporting hazardous materials or wastes. Placards are used to determine potential hazards in the event of a spill and are placed on all four sides of a vehicle so that HAZMAT teams, fire, emergency, medical, and other personnel who respond to accidents may quickly identify the contents and associated hazards. Placards are required if one thousand pounds or more of a hazardous material is transported and if any amount of material classified as explosive, poisonous, radioactive, or a flammable solid is transported.

The DOT classifies materials based on nine hazard classes represented by symbols. The classes are explosives, gases, flammable liquids, flammable solids, oxidizers, poisonous materials, biohazards, radioactive materials, corrosives, or other regulated materials.

The routes that transporters of hazardous waste use must be carefully considered to minimize the risk of an accidental release. If possible, densely populated areas should be avoided. The type of highway or road and the weather conditions along the route must also be considered. Risk analysis may become important in selecting routes for hazardous waste transport in order to minimize adverse impacts to human health in case of an accidental release.

Municipal Waste

Due to rapidly decreasing space in urban landfills, officials have been forced to find alternate locations for municipal waste disposal. This has created significant financial incentives for rural communities to accept garbage from urban areas. Depending on the location of these rural facilities, it may be necessary to transport large quantities of wastes by a variety of methods, most often by truck, railway, or barge.

Many citizens are concerned about the transportation of the waste through their communities and the risks involved. People are also concerned that the municipal waste from urban areas may be contaminated with toxic chemicals or substances that could contaminate local drinking water supplies.

Disposal of hazardous wastes in the United States can cost up to $2,500 per ton. This has led to the practice of selling waste to developing countries for disposal at a much lower cost. This international waste trade may be illegal in some instances, but the hefty sum paid to those who accept the wastes remains tempting to developing countries.

However, the actual composition of the wastes received by developing countries is often misrepresented by those selling the waste. In addition, most developing countries lack the resources and technical expertise to safely manage these hazardous wastes.

Trade in hazardous wastes is a global issue. About ten percent of all hazardous wastes generated around the world cross international boundaries. A large portion goes from industrialized countries to developing countries where disposal costs are lower.

Although developing countries may lack the financial and technical capacities to clean up hazardous waste releases in their countries, these countries nevertheless are sites for treatment, recycling, and disposal of wastes from abroad.

The Basel Convention on the Control of the Transboundary Movement of Hazardous Wastes and Their Disposal is the first global environmental treaty to control the international trade of waste. Under the Convention, trade in hazardous wastes cannot take place without the consent of the importing country and cannot occur under conditions that are assessed as not environmentally sound.

As of April 2002, 150 countries had ratified the convention. A new protocol adopted by the convention in 2000 provides the first international framework establishing liability for damages that may result from the transportation or disposal of hazardous wastes across foreign borders

Waste Reduction

Waste reduction, also known as source reduction, is the practice of using less material and energy to minimize waste generation and preserve natural resources. Waste reduction is broader in scope than recycling and incorporates ways to prevent materials from ending up as waste before they reach the recycling stage. Waste reduction includes reusing products such as plastic and glass containers, purchasing more durable products, and using reusable products, such as dishrags instead of paper towels.

Donating products, from office equipment to eyeglasses and clothing, reduces the amount of material manufactured overall. Purchasing products that replace hazardous materials with biodegradable ingredients reduces pollution as well as waste.

In general, waste reduction offers several environmental benefits. Greater efficiency in the production and use of products means less energy consumption, resulting in less pollution. More natural resources are preserved. Products using less hazardous materials are used. Finally, less solid waste ends up in landfills.

Waste reduction also means economic savings. Fewer materials and less energy is used when waste-reduction practices are applied. Rather than using the traditional cradle-to-grave approach, a cradle-to-cradle system is adopted. In this cradle-to-cradle system, also called industrial ecology, products are not used for a finite length of time. Instead of disposing of materials, or the components of a product after a single use, products are passed on for further uses. This is considered a flow of materials.

This can be applied within an organization, or between organizations that may be considered unrelated, on a cooperative basis. For example, a cotton manufacturer sends its unwanted scraps to an upholsterer, who uses the scraps as stuffing in chairs. When the life span of the chair is reached, the materials are returned to the manufacturer, who reuses the parts with endurance.

The damaged upholstery, which was originally created using nonhazardous materials, is sold to a local farmer who uses it in composting. Money is also saved through reduced purchasing. Waste-disposal costs are decreased because fewer materials end up as waste.

Waste can be reduced by individuals, businesses, institutions such as hospitals or educational facilities, organizations, municipalities, or government agencies. There are several ways individuals can practice waste reduction:
  1. Reusing products. This could mean reusing file folders rather than throwing them away after one use, or refilling water bottles; 
  2. Using products more efficiently. This could mean using both sides of paper in photocopying; and 
  3. Donating or exchanging products or materials that may seem useless, but that another party may find valuable. For example, the chair manufacturer mentioned above had no internal use for the scrap upholstery leftover after recycling the more durable parts of the used chairs. However, a cooperative agreement with a local farmer allowed the scraps to be used once again, benefiting the farmer by adding to his compost.

The EPA’s WasteWise Program

The Environmental Protection Agency (EPA) lists waste reduction and reuse as top priorities in its solid waste management hierarchy, followed by recycling, composting, waste-to-energy, and landfilling. Many governments and businesses have adopted the practice of waste reduction.

The EPA offers a free, comprehensive waste-reduction program to businesses, organizations, and municipalities. The program, called WasteWise, offers educational and technical assistance in developing, executing, and measuring waste-reduction activities. Through WasteWise, groups can design and maintain a waste-reduction program that is flexible to their specific needs. The nationwide program was started in 1994, and it had over eleven hundred participating partners in 2002.

Large corporations, universities, and cities across the country have seen significant benefits, both economically and environmentally, by using WasteWise.

The National Recycling Coalition Recommendations

The National Recycling Coalition lists several steps that purchasing departments of organizations can use in their waste-reduction strategies:
  1. Reduce product use. Adopt the practice of printing on both sides of office paper.
  2. Rent or lease products or equipment. This includes leasing, rather than purchasing, equipment such as photocopiers, which can become obsolete, leaving the organization with old, unnecessary, and sometimes hazdardous equipment to discard.
  3. Purchase remanufactured or rebuilt products, or products that can be refurbished.
  4. Purchase more durable products. Higher-quality products typically have a longer life cycle.
  5. Purchase products that use nonhazardous materials. Nonhazardous materials are safer for individuals and landfills.
  6. Purchase returnable, reusable, or refillable products. For instance, transport containers can be reused.
  7. Purchase products in bulk.
  8. Purchase products that reuse packaging or use less packaging.
  9. Share and reuse resources within the organization. Companies can implement an internal computer equipment and office supply exchange before purchasing new products.

The EPA reports that 232 million pounds of waste were generated in 2000. The amount of waste produced per person has grown over the last thirty-five years, from 2.7 to 4.6 pounds per day. In 1999, waste reduction saved over fifty million tons of municipal solid waste from being dumped into landfills.

Waste to Energy

Waste to energy (WTE) is the term used to describe the conversion of waste by-products into useful steam or steam-generated electricity. Typically, WTE is produced by converting municipal solid waste (MSW), which is defined as residential and commercial refuse, and makes up the largest source of waste in industrialized countries.

This industry has been producing heat and power in the United States for a century, and there are currently more than one hundred WTE plants nationwide. Recently, however, the definition of waste has been expanded from MSW to include wastes such as wood, wood waste, peat, wood sludge, agricultural waste, straw, tires, landfill gases, fish oils, paper industry liquors, railroad ties, and utility poles.

In 1999 these by-products produced approximately 3.2 quadrillion BTUs (i.e., 1 × 10^15) British thermal units, which is also known as a quad) of energy out of approximately 97.0 quads of energy consumed in the United States.

Nearly thirty million tons of trash are processed each year in WTE facilities to generate steam and electricity. The benefits to society include the following: preventing the release of greenhouse gases such as methane into the atmosphere if the trash were landfilled; reducing the impact on landfills by reducing the volume of the waste 80 to 90 percent; providing an alternative to coal use, which prevents the release of emissions such as nitrogen oxides into the atmosphere; and saving the earth’s natural resources by using less oil, coal, or natural gas for electricity generation.

The Process of Converting Waste to Energy

Generally, WTE facilities can be divided into two process types: mass burn and refuse-derived fuel (RDF). Mass burn facilities process raw waste that has not been shredded, sized, or separated before combustion, although large items such as appliances and hazardous waste materials and batteries are removed before combustion.

In mass burn systems, untreated MSW is simply burned, with the heat produced converted into steam, which can then be passed through a steam turbine to generate electricity or used directly to supply heat to nearby industries or buildings.

RDF is a result of processing MSW to separate the combustible fraction from the noncombustibles, such as metals and glass. RDF is mainly composed of paper, plastic, wood, and kitchen or yard wastes, and has a higher energy content than untreated MSW. Like MSW, RDF is then burned to produce steam and/or electricity.

A benefit of using RDF is that it can be shredded into uniformly sized particles or compressed into briquettes, both of which facilitate handling, transportation, and combustion. Another benefit of RDF rather than raw MSW is that fewer noncombustibles such as heavy metals are burned.

Energy Production from Waste in the United States and South America

South America, with its agrarian societies, surprisingly consumes very few wastes for the production of steam or electricity. Brazil is the largest country in South America and is also the largest energy consumer, consuming about 8.5 quads of energy each year as compared to 6.1 quads for Mexico, 12.5 quads for Canada, and 97.0 quads for the United States.

Due to the large size of Brazil’s agricultural sector, biomass is seen as the best future alternative energy source. Currently, Brazil produces about 4,000 gigawatt (1 × 10^9) hours annually (i.e., 0.1 quads equivalent) in the sugar industry to run its own refineries and distilleries.

At the same time, Brazil produces up to 3.9 billion gallons of ethanol (i.e., 0.5 quads equivalent) for automobiles each year, although it is manufactured from sugar and not waste materials. No other South American countries produce significant quantities of energy from waste; however, Argentina’s biomass energy use, like Brazil’s, is expected to grow in the coming years.

In the United States, corn is the primary feedstock along with barley and wheat that is currently being used to produce ethanol, although neither corn or grains are considered wastes. Considerable ongoing research is exploring the use of true biomass wastes such as corn stover or wood chips and sawdust for ethanol production. One project at the U.S. Department of Energy involves the cofiring of sawdust and tires with coal in utility boilers.

Domestic Wastewater Treatment

Wastewater is treated to remove pollutants (contaminants). Wastewater treatment is a process to improve and purify the water, removing some or all of the contaminants, making it fit for reuse or discharge back to the environment. Discharge may be to surface water, such as rivers or the ocean, or to groundwater that lies beneath the land surface of the earth. Properly treating wastewater assures that acceptable overall water quality is maintained.

In many parts of the world health problems and diseases have often been caused by discharging untreated or inadequately treated wastewater. Such discharges are called water pollution, and result in the spreading of disease, fish kills, and destruction of other forms of aquatic life. The pollution of water has a serious impact on all living creatures, and can negatively affect the use of water for drinking, household needs, recreation, fishing, transportation, and commerce.

Objectives and Evolution of Wastewater Treatment

We cannot allow wastewater to be disposed of in a manner dangerous to human health and lesser life forms or damaging to the natural environment. Our planet has the remarkable ability to heal itself, but there is a limit to what it can do, and we must make it our goal to always stay within safe bounds. That limit is not always clear to scientists, and we must always take the safe approach to avoid it.

Basic wastewater treatment facilities reduce organic and suspended solids to limit pollution to the environment. Advancement in needs and technology have necessitated the evolving of treatment processes that remove dissolved matter and toxic substances. Currently, the advancement of scientific knowledge and moral awareness has led to a reduction of discharges through pollution prevention and recycling, with the noble goal of zero discharge of pollutants.

Treatment technology includes physical, biological, and chemical methods. Residual substances removed or created by treatment processes must be dealt with and reused or disposed of in a safe way. The purified water is discharged to surface water or ground water. Residuals, called sludges or biosolids, may be reused by carefully controlled composting or land application. Sometimes they are incinerated.

Since early in history, people have dumped sewage into waterways, relying on natural purification by dilution and by natural bacterial breakdown. Population increases resulted in greater volume of domestic and industrial wastewater, requiring that we give nature a helping hand. Some so-called advancements in cities such as Boston involved collecting sewage in tanks and releasing it to the ocean only on the outgoing tide. Sludge was barged out to sea so as to not cause complaint.

Until the early 1970s, in the United States, treatment mostly consisted of removal of suspended and floating material, treatment of biodegradable organics, and elimination of pathogenic organisms by disinfection. Standards were not uniformly applied throughout the country.

In the early 1970s until about 1980, aesthetic and environmental concerns were considered. Treatment was at a higher level, and nutrients such as nitrogen and phosphorus were removed in many localities.

Since 1980, focus on health concerns related to toxics has driven the development of new treatment technology. Water-quality standards were established by states and the federal government and had to be met as treatment objectives. Not just direct human health but aquatic-life parameters were considered in developing the standards.

Wastewater Treatment Types

Rural unsewered areas, for the most part, use septic systems. In these, a large tank, known as the septic tank, settles out and stores solids, which are partially decomposed by naturally occurring anaerobic bacteria. The solids have to be pumped out and hauled by tank truck to be disposed of separately. They often go to municipal wastewater treatment plants, or are reused as fertilizer in closely regulated land-application programs. Liquid wastes are dispersed through perforated pipes into soil fields around the septic tank.

Most urban areas with sewers first used a process called primary treatment, which was later upgraded to secondary treatment. Some areas, where needed, employ advanced or tertiary treatment. Common treatment schemes are presented in the following paragraphs.

Primary Treatment. 

In primary treatment, floating and suspended solids are settled and removed from sewage. Flow from the sewers enters a screen/bar rack to remove large, floating material such as rags and sticks.

It then flows through a grit chamber where heavier inorganics such as sand and small stones are removed.

Grit removal is usually followed by a sedimentation tank/clarifiers where inorganic and organic suspended solids are settled out.

To kill pathogenic bacteria, the final effluent from the treatment process is disinfected prior to discharge to a receiving water. Chlorine, in the form of a sodium hypochlorite solution, is normally used for disinfection. Since more chlorine is needed to provide adequate bacteria kills than would be safe for aquatic life in the stream, excess chlorine is removed by dechlorination. Alternate disinfection methods, such as ozone or ultraviolet light, are utilized by some treatment plants.

Sludge that settles to the bottom of the clarifier is pumped out and dewatered for use as fertilizer, disposed of in a landfill, or incinerated. Sludge that is free of heavy metals and other toxic contaminants is called Biosolids and can be safely and beneficially recycled as fertilizer, for example.

Secondary Treatment

Primary treatment provided a good start, but, with the exception of some ocean outfalls, it is inadequate to protect water quality as required by the Environmental Protection Agency (EPA).

With secondary treatment, the bacteria in sewage is used to further purify the sewage. Secondary treatment, a biological process, removes 85 percent or more of the organic matter in sewage compared with primary treatment, which removes about 50 percent.

The basic processes are variations of what is called the “activated sludge” process or “trickling filters,” which provide a mechanism for bacteria, with air added for oxygen, to come in contact with the wastewater to purify it.

In the activated sludge process, flow from the sewer or primary clarifiers goes into an aeration tank, where compressed air is mixed with sludge that is recycled from secondary clarifiers which follow the aeration tanks. The recycled, or activated, sludge provides bacteria to consume the “food” provided by the new wastewater in the aeration tank, thus purifying it.

In a trickling filter the flow trickles over a bed of stones or synthetic media on which the purifying organisms grow and contact the wastewater, removing contaminants in the process. The flow, along with excess organisms that build up on the stones or media during the purification, then goes to a secondary clarifier.

Air flows up through the media in the filters, to provide necessary oxygen for the bacteria organisms. Clarified effluent flows to the receiving water, typically a river or bog, after disinfection. Excess sludge is produced by the process and after collection from the bottom of the secondary clarifiers it is dewatered, sometimes after mixing with primary sludge, for use as fertilizer, disposed of in a landfill, or incinerated.

Advanced or Tertiary Treatment

As science advanced the knowledge of aquatic life mechanisms and human health effects, and the need for purerwater was identified, technology developed to provide better treatment. Heavy metals, toxic chemicals and other pollutants can be removed from domestic and industrial wastewater to an increasing degree. Methods of advanced treatment include microfiltration, carbon adsorption, evaporation /distillation, and chemical precipitation.

Marine Pollution

Marine pollution is the release of by-products of human activity that cause harm to natural marine ecosystems. The pollutants may be sewage, farm waste, toxic chemicals, or inert materials that may smother, choke, or strangle living organisms.

Sewage, Animal Waste, and Fertilizers

Sewage, animal waste, and chemical fertilizers all have a high content of nitrogen and phosphorus. Artificially high levels of these substances in the water promote excessive growth of microscopic or macroscopic plants, in a process called eutrophication. When these plants accumulate, die, and decay, they cause low oxygen content in the water. Even if sewage is treated to remove solids, the liquid discharged contains high levels of nitrogen and phosphorus.

Intensive cultivation of animals in feedlots, or application of more fertilizer than a crop can absorb, also cause runoff rich in nitrogen and phosphorus that find their way into rivers and estuaries. Vehicle exhausts and industrial chimneys are large sources of nitrogen compounds that are transported in the atmosphere and deposited in coastal waters.

On a global scale, agricultural runoff is the most important source of eutrophication, but atmospheric deposition is the fastest-growing source. It is the largest source of nitrogen off the coast of the northeastern United States, in the western Baltic Sea, and in the western Mediterranean Sea. International agencies consider that, worldwide, eutrophication is the most serious pollution problem in coastal waters.

For example, in the Gulf of Mexico, off the mouth of the Mississippi River, water near the bottom has severely reduced oxygen content over a very large area, sixteen thousand square kilometers (6,200 square miles) by 1998. Mobile animals such as fish and shrimp leave the hypoxic area, but sedentary animals such as clams and worms are killed in large numbers.

A classic example of eutrophication and its treatment occurred in the estuary of the River Thames, near London, England. In the 1950s the water was severely hypoxic for thirty-five kilometers (twenty-two miles) below London Bridge. After several sewage treatment plants were built, the water returned to a well-oxygenated state and migratory fish such as salmon once again ascend the river.

In the case of the Mississippi River, treatment of the eutrophication is more difficult because runoff from agricultural land is the major cause of the problem, and more than half of the agricultural land in the United States drains into the Mississippi basin. Cleaning up the pollution would involve changes in farming methods on a national scale.

Eutrophication has important indirect effects. The plants known as sea grasses, which grow in the shallow water of estuaries, provide food and shelter for a wide range of animals, including geese, turtles, manatees, and fish. In eutrophicated water, the dense microscopic plant life significantly reduces the penetration of light and smothers the sea grasses.

In Chesapeake Bay, Maryland, eutrophication caused an area of sea grasses to decrease by two-thirds between 1960 and 1980, and there was a corresponding decrease in landings of fish and crabs. Similar effects have been observed in Australia.

Red tides, or harmful algal blooms, are associated with eutrophication. Single species of phytoplankton multiply at the expense of all other species and become so abundant that the water is discolored. Many bloom species produce toxic substances. During the 1990s in estuaries located in the south-eastern United States, there were numerous cases of blooms of Pfiesteria piscida, a dinoflagellate that produced a toxin which killed thousands of fish.

The source of the nutrients support Pfiesteria is believed to be agricultural runoff or sewage discharge. Other types of blooms are ingested by shellfish, which become toxic for humans who consume them, causing partial paralysis, memory loss, or even death. Toxic blooms have been reported much more frequently in the 1990s than in the past, and the spread of eutrophication is believed to be a contributing factor.

Pollution and Coral Reefs

On coral reefs, eutrophication causes seaweed to grow and smother the corals. Several kinds of environmental problems interact with eutrophication to cause the deterioration of coral reefs. Overharvesting of the fish and invertebrates that eat seaweed accelerates the smothering.

Careless development along coastlines and in river basins leads to soil erosion and the transport of heavy loads of silt and clay, which settle on the corals and smother them. Oil spills also take their toll. When corals are exposed to abnormally high water temperature, they respond by discharging the microscopic algae living within their tissues. Sometimes they recover, but often they die.

These episodes, called coral bleaching, became much more frequent during the 1990s and are believed to be caused by global warming. The result of pollution and global warming is that at least half of the area of coral reefs in south-east Asia is in poor condition, and in parts of the Caribbean Sea only 5 percent of the reef area consists of living coral.

Metals and Organic Contaminants

Industrial effluents often contain metallic compounds. For example, Halifax, a small city in eastern Canada, discharged into its harbor during the 1990s about thirty-three tons of zinc and thirty-one tons of lead per year, with lesser amounts of copper and other metals. These metals are held in the sediment in a relatively inert form, but if stirred up into the water column, they become oxygenated and toxic.

Tin is another common pollutant in harbors. It occurs as tributyltin (TBT), which is used as a component of antifouling paints on the undersides of ships. When taken up by shellfish, it accumulates in their tissues and has proved toxic to the shellfish and to organisms that consume them. The United States began to phase out TBT in 1988, and it will be banned internationally beginning in 2008.

Industry also produces organic compounds such as polychlorinated biphenyls (PCBs) and various pesticides. These accumulate in the fatty tissue of plants and animals low in the food chain, and as they pass through the food web to larger and long-lived animals, there is an increase in concentration of the substances in their fat, a process known as bioaccumulation. The St. Lawrence River, which drains the Great Lakes, has accumulated large amounts of organochlorines, which have amassed in the tissues of Beluga whales.

During the 1990s, the level of this pollution was much reduced, and the whales have been protected from hunting, but their population fails to increase. Many animals have tumors and disease. There is mounting evidence that chronic exposure to contaminants causes suppression of the immune responses of marine mammals. Similar problems have occurred with seals in the Baltic Sea.

Marine Debris

Marine beaches serve as natural traps for marine debris. Globally, the most common materials are plastics, followed by glass and metal. The chief dangers to marine life result from the ingestion of these fragments, which may block the gut, and from entangling, which may cause suffocation or prevent locomotion and feeding.

In a survey of U.S. beaches close to urban centers, cigarette butts were the most abundant debris, followed by packaging items (boxes, bags, caps, lids), medical waste, and sewage. A high proportion of this material reached the sea by way of sewers. Even street litter can be washed into surface drains and then to the sea. The dumping of sewage and waste by ships is another source.

Public revulsion at the state of U.S. beaches was a key factor in the enactment of stronger environmental protection laws, like the Ocean Dumping Ban Act of 1988 that prohibited the dumping of sewage into the ocean. On sites more remote from cities, pieces of rope and netting are the most common types of marine debris.