Primary waste water treatment involves such physical techniques as screening large debris, skimming off floating materials, and settling out suspended material in tanks. These techniques remove about 60% of suspended solids and 35% of biodegradable organic material in municipal sewage as well as in comparable industrial waste water. Secondary treatment biologically breaks down organic matter remaining from the primary treatment by using microorganisms to decompose the wastes. This method increases the total removal of suspended solids and biodegradable organics to 90%. As a final step, municipal sewage is chlorinated to kill any pathogenic microorganisms.
Sludge--the settled material from waste water treatment--can be reduced in volume by digestion in special airtight tanks, composting (an oxygen-requiring digestion), dewatering, or incineration. Energy or materials recovery may accompany these techniques and may even replace final disposal in landfills or the ocean. For example, some sludges may be applied to the land, recycling their plant nutrients.
Advanced treatment of waste involving biological, chemical, and physical methods of disposal is used either to remove plant nutrients that promote excessive growth of algae in water or to remove industrial pollutants, such as heavy metals and nonbiodegradable organic chemicals. The advanced treatment system at South Lake Tahoe, for instance, produces an effluent that meets drinking-water standards. The system enhances primary- and secondary-treatment coagulation and settling of solid wastes containing phosphorus; it removes nitrogen by means of gas stripping; and it has an activated-carbon absorption and filtration stage. Although effective, advanced systems are much more costly than secondary treatment systems.
TREATMENT SYSTEMS FOR AIR
Techniques for the removal of air pollutants from stationary sources are distinguished between those which remove particulate matter and those which remove gases. Four techniques, varying in cost and efficiency, for removing particulates are the long-cone cyclone separator, the wet scrubber, the electrostatic precipitator, and the baghouse. The cyclone separator causes air emissions to whirl around, forcing heavy particles to the outside and ultimately to removal below. The wet scrubber essentially washes particulates out of the exhaust with a water spray. The electrostatic precipitator electrically charges the particles and attracts them to charged plates, thereby removing them from the exhaust stream. The baghouse operates like a vacuum cleaner, trapping particles in fabric filters placed in the exhaust stream.
Extremely small particulates are the most dangerous because they can penetrate deeply into human lungs. When assessing removal efficiencies, therefore, it is important to determine the amount of smaller particles removed as well as the total removal of particulates of all sizes. Although the baghouse has the best removal efficiency, the electrostatic precipitator is more commonly used because of its lower cost.
Gaseous emissions are in general more difficult to control than particulates. Automobile emissions have been reduced by lowering engine combustion temperatures and by completing the oxidation of unburned gases by means of a catalytic converter in the exhaust system.
One of the most difficult air pollutants to control is sulphur dioxide, which is given off in the combustion of sulfur-containing fuels, particularly coal in power plants. The projected replacement of dwindling oil supplies with coal makes this a critical problem. Removal of sulphur dioxide from exhaust gases can be accomplished with devices called scrubbers. Limestone scrubbers, for instance, have a reported removal efficiency of up to 90% of sulphur dioxide. They are, however, very expensive; they consume about 5% of a power plant's output; and they create massive amounts of calcium sulfite sludge, which must be disposed of as waste. Research is being done on catalytic scrubbers, which use reagents that can be separated from the sludge; the reagent can then be recycled, whereas the remaining sludge may contain economically usable sulphur or sulphuric acid.
PROBLEMS IN POLLUTION CONTROL
Pollution-treatment systems have been effective in reducing the massive quantities of water and air pollutants that have clogged and choked urban areas. Although the improvements have been significant, recent pollution-control legislation aims to go further in order to control the less visible but often hazardous chemical and gaseous pollutants that still contaminate many waterways and urban atmospheres.
The costs of pollution control--resulting from capital, maintenance, and labor costs, as well as from the cost of additional residuals disposal--generally go up rapidly as a greater percentage of residuals is removed from the waste stream. Damage from pollution, on the other hand, goes down as a greater amount of contaminants is removed. Theoretically, the level of treatment should correspond to a point at which total costs of treatment and of damage to the environment are minimised or the benefits of further treatment are proportionally much smaller than the increased cost. In reality, costs or damages resulting from pollution can rarely be assessed in terms of dollars.
In addition, extensive treatment may result in more residuals and may involve a trade-off of one form of pollution for another. For example, although advanced waste water treatment at South Lake Tahoe produces a drinkable effluent, the process requires extensive chemical and energy inputs and releases ammonia and other pollutants into the air; also, the chemical sludge produced must be disposed of on land.
Because of these economic and residual trade-off problems associated with the more advanced treatment systems, complete reliance on them to meet the goals of federal legislation may not be appropriate. In many cases the development of processes that either reduce residuals or convert them into usable products can extensively reduce the cost of treatment. The conversion to clean energy sources, new combustion processes for coal, and advanced scrubbers are approaches that may reduce total residuals at a lower cost than present methods. These methods of pollution control may be the most efficient in minimising the effects of industrial activity on people and the environment.
Nuclear energy
nuclear energy, the energy stored in the nucleus of an ATOM and released through fission, fusion, or RADIOACTIVITY. In these processes a small amount of mass, equal to the difference in mass before and after the reaction, is converted to energy according to the relationship E = mc2, where E is energy, m mass, and c the speed of light (see RELATIVITY). In fission processes, a fissionable nucleus absorbs a neutron, becomes unstable, and splits into two nearly equal nuclei. In fusion processes, two nuclei combine to form a single, heavier nucleus. Fission occurs for very heavy nuclei, while fusion occurs for the lightest nuclei. Nuclear fission was discovered in 1938 by Otto HAHN and Fritz Strassman, and was explained in 1939 by Lise MEITNER and Otto Frisch. Fission energy can be obtained by bombarding the fissionable isotope URANIUM-235 with slow neutrons in order to split it. Because this reaction releases an average of 2.5 neutrons, a chain reaction is possible, provided at least one neutron per fission is captured by another nucleus and causes a second fission. In an ATOMIC BOMB the number of neutrons producing additional fission is greater than 1, and the reaction increases rapidly to an explosion. In a NUCLEAR REACTOR, where the chain reaction is controlled, the number must be exactly 1 in order to maintain a steady reaction rate. Uranium-233 and PLUTONIUM-239 can also be used but must be produced artificially. Moreover, the fuel for fusion reactors, deuterium, is readily available in large amounts. Temperatures greater than 1,000,000°C are required to initiate a fusion, or thermonuclear, reaction. In the HYDROGEN BOMB such temperatures are provided by the detonation of a fission bomb. Sustained, controlled fusion reactions, however, require the containment of the nuclear fuel at extremely high temperatures long enough to allow the reactions to take place. At these temperatures the fuel is a PLASMA, and magnetic fields have been used in attempts to contain this plasma. To produce fusion energy, scientists have also used high-powered laser beams aimed at tiny pellets of fission fuel. In 1994 U.S. researchers achieved a fusion reaction that lasted about a second and generated about 10.7 million watts, using deuterium and tritium in a magnetically confined plasma. The use of tritium lowers the temperature required and increases the rate of the reaction, but it also increases the release of radioactive NEUTRONS.
NUCLEAR ENERGY TODAY
In the 50 years since the discovery of fission, nuclear power has become a major source of the world's electric energy. At the end of 1989 there were 416 nuclear plants operating worldwide, generating about 17% of the world's electricity, with another 130 in the design or construction stages. Nuclear plants operate in 27 nations, and 5 additional nations have them under construction.
The nuclear energy program in the United States is the world's largest: 108 operating plants (1989) have a capacity of about 100,000 MW and provide nearly 20% of U.S. power generation. Nuclear power is now the second largest source of U.S. electricity, exceeded only by coal, which provides about 55% of the country's electricity. Other contributors to electric generation include natural gas (9%), oil (6%), and hydropower (9%). The nuclear fraction is expected to reach about 25% during the 1990s.
In general, nuclear plants are more complex and costly to build than plants using fossil fuels--although the cost of fuel for nuclear plants is significantly lower. On balance, the fuel cost difference is such that nuclear electricity is cheaper than fossil electricity for most nations. For the industrialised countries of Europe and Asia the difference in cost may be as large as a factor of two.
The French Nuclear Program
The French nuclear program was begun in the 1940s in order to create a nuclear weapons capability. As in the U.S. program, the first French reactors were built for plutonium production. The first French commercial units, which used air as a coolant, were in operation by 1957. Their operation was a technical, but not an economic, success. As a result, in 1970, the French adopted the U.S. light-water technology. Subsequently, the French have built 54 domestic reactors with 9 more under construction. The French standardised their designs to improve the efficiency of construction and operation. They have also built units for Belgium, South Africa, South Korea, and China.
The Japanese Nuclear Program
The Japanese also have a vigorous and successful nuclear program. Lacking any significant indigenous energy resources, in 1955 the Japanese government selected nuclear power as its major electric-supply technology. The program has carefully nurtured the internal capability to manufacture equipment and construct nuclear plants, to operate a high-quality power system, and to provide complete technology for the entire fuel cycle. The utilities in Japan have become leaders in plant operation; and by 2020 the nuclear-fueled portion of Japan's electric supply is expected to exceed 50 percent. In the future the Japanese plan to exploit the potential of BREEDER REACTORS, which convert non fissionable U-238 into fissionable plutonium-239. A successful breeder reactor program could eliminate Japan's need to import any fuels for the production of electricity. To date, however, the cost of electricity from breeders exceeds the cost from conventional light-water reactors. The Japanese long-range policy assumes that uranium fuel will ultimately become scarce, making the breeder technology economical.
The Slowdown in Other National Programs
Nuclear power programs in most other countries have come to a virtual standstill. (In the United States there has not been an order for a new plant since the mid-1970s.) A major cause has been the move toward increased efficiency in the consumption of oil, and a drop in energy demand. Equally significant have been concerns about the safety of nuclear reactors and an increasing awareness of the problems created by nuclear waste.
Public opinion remained largely favorable toward nuclear energy until the Three Mile Island (TMI) reactor accident in the spring of 1979. The accident began with the failure of some of the plant hardware. By itself, the failure would not have caused serious damage to the reactor, but a series of mistakes in interpreting the condition of the reactor led to more mistakes, which removed reactor coolant and caused a sizable portion of the fuel to melt. Although there was extensive damage to the reactor, the containment system functioned, preventing the release of much radioactivity to the environment. Nevertheless, there was widespread apprehension for several days among the nearby population. The events at TMI captured the attention of the world, dominated the media for days, and caused a historic shift in attitudes toward nuclear power.
The accident also had serious impacts on the licensing of new plants. Regulations were drastically modified to prevent a recurrence of the events of TMI. The modifications complicated the construction of new plants as well as the operation of existing plants. Construction times expanded from about 6 years to more than 12 years, and plant costs accelerated rapidly because of the new requirements.
Another factor contributing to the stagnation of new construction was the intervention by anti-nuclear groups in licensing proceedings for new plants. Such intervention has proven to be time consuming and costly to the industry, particularly for those plants in the late stages of construction, when interest costs mount on the billions that have been borrowed. The Shore ham (New York) and Sea brook (New Hampshire) plants are notable examples of cost overruns, caused in part by completion delays.
Although few other countries permit the extent of public intervention in licensing hearings that is allowed in the United States, all the major nuclear nations impose strict regulations on their nuclear energy plants. Nevertheless, studies indicate that, for the most part, the U.S. industry performs far less efficiently than do those in Switzerland, Germany, France, and Japan. A key factor in their superior performance may be the cooperation that exists between the industries and their suppliers and regulators--a cooperation that, until recently, was not apparent in the United States.
In its early years, nuclear power was cost competitive with coal. Some of the cheapest sources of electricity in the United States today are nuclear plants built in the period before TMI. The current environment, however, has made nuclear power an uneconomical choice for U.S. utilities. Chernobyl
The accident in April 1986 at the CHERNOBYL plant in the USSR was as devastating as a nuclear accident can be. A very large amount of radioactive material--between 30% and 50% of the total material in the reactor--was released. Radioactive fallout from the event spread, forcing the long-term evacuation of over 100,000 local people and causing the pollution of foods in large portions of Europe.
The Chernobyl reactor design uses water as a coolant and graphite as the moderator. This type of reactor is known to be hazardous and is used only in the USSR. (Such a design would not be licensed in the Western nations.) Nevertheless, the accident has profoundly influenced worldwide public acceptance of nuclear power. It is too early to know whether or not the Chernobyl accident has permanently crippled the future of nuclear power in industrialised countries.
Approximately 80% of our air pollution stems from hydrocarbons released by vegetation, so let's not go overboard in setting and enforcing tough emission standards from man-made sources.
global warming, gradual increase of the temperature of earth's lower atmosphere as a result of human activity. A layer of atmospheric gases (carbon dioxide, methane, nitrous oxide, and ozone; called greenhouse gases) allows radiation from the sun to reach the earth unimpeded and traps INFRARED RADIATION from the earth's surface. This process, called the GREENHOUSE EFFECT, keeps the earth's temperature at a level suitable for life. Growth in industry, agriculture, and transportation since the Industrial Revolution, however, has produced gases that have augmented the earth's thermal blanket. Some researchers believe that continued production of greenhouse gases will lead to global temperature increases, which could melt the polar ice sheets, resulting in a rise in sea level and damage to coastal development and estuaries; dry soils, producing profound changes in agriculture; endanger many species; and spawn more frequent tropical storms. Despite controversy over this scenario, many nations have acted to decrease greenhouse-gas production-over 150 nations have signed a 1992 treaty designed to reduce the emission of such gases-and control deforestation, which also contributes to higher levels of carbon dioxide.
Pollution can also incress the risk of Cancer!
waste disposal, generally, the disposal of waste products resulting from human activity. Once a routine concern, the disposal of waste has become a pressing problem in the 20th cent. because of the growth of population and industry and the toxicity of many new industrial byproducts. Traditionally, waste was often dumped into nearby streams. Sewer systems, which date back at least to the 6th cent. B.C. in Rome, were widely introduced in U.S. cities in the mid-19th cent. In the absence of sewerage, waste has often been stored in underground cesspools, which leach liquids into the soil but retain solids, or in simple sewage tanks, e.g., septic tanks, in which organic matter disintegrates. Raw sewage is now commonly treated before being discharged as effluent, usually by reducing solid components to a semiliquid sludge. Although sludge can be processed, e.g., as fertilizer, it has often been buried or dumped at sea, a practice outlawed in the U.S. since 1992. Some recent systems have employed artificial wetlands to treat waste water. Most solid waste in the U.S., such as municipal refuse, is deposited in open dumps. More sophisticated methods of disposal include the sanitary landfill, where waste is spread thin and separated by layers of tamped earth, and special incinerators that burn combustible waste while generating steam (for heating) and/or gases (to run turbines). The recycling of noncombustible products such as glass and metals, e.g., aluminum cans, is growing and offers long-range hope for disposal. Toxic wastes include many chemicals, some generated in substantial quantities as common industrial byproducts, e.g., heavy metals (notably mercury, lead, and cadmium), certain hydrocarbons, and some poisonous organic solvents. Although detoxification using bacteria, irradiation, and chemical systems is now being performed with more frequency, such substances have traditionally been sealed in metal drums and deposited underground or in the ocean. The containers have often corroded and leaked their contents, polluting the land and water supply and prompting the U.S. Congress to pass the 1980 "Superfund" act, which assigned broad financial responsibility for toxic waste cleanup. One of the greatest modern hazards is radioactive waste, produced in increasing amounts as byproducts of research, nuclear weaponry, and nuclear-power generation and particularly dangerous because many kinds remain lethal for thousands of years. In the U.S., these materials are now stored in temporary sites; permanent storage solutions have encountered many technical difficulties and public objections to specific sites. A process to solidify nuclear waste and reduce its potential danger as a contaminant is one option. Highly radioactive waste is expected to be stored permanently underground at Yucca Mt., Nev., but the site will not be ready until 2010.
Environment
Hazardous Waste Sites in the U.S.
Source: Environmental Protection Agency, Natl. Priorities List, May 1994
State/Territory General Federal Total*
Alabama 9 3 13
Alaska 2 6 8
Arizona 7 3 10
Arkansas 12 0 12
California 69 22 96
Colorado 13 3 18
Connecticut 14 1 16
Delaware 18 1 19
District of Columbia 0 0 0
Florida 49 5 57
Georgia 11 2 13
Hawaii 0 3 4
Idaho 6 2 10
Illinois 33 4 37
Indiana 32 0 33
Iowa 16 1 19
Kansas 9 1 10
Kentucky 19 1 20
Louisiana 11 1 13
Maine 7 3 10
Maryland 8 4 13
Massachusetts 22 8 30
Michigan 76 0 77
Minnesota 37 3 41
Mississippi 2 0 4
Missouri 20 3 23
Montana 8 0 8
Nebraska 7 1 10
Nevada 1 0 1
New Hampshire 16 1 17
New Jersey 101 6 108
New Mexico 7 2 11
New York 79 4 85
North Carolina 20 1 22
North Dakota 2 0 2
Ohio 31 3 38
Oklahoma 9 1 11
Oregon 9 1 12
Pennsylvania 95 5 101
Rhode Island 10 2 12
South Carolina 22 1 24
South Dakota 2 1 4
Tennessee 12 3 17
Texas 25 4 30
Utah 8 4 16
Vermont 8 0 8
Virginia 19 5 25
Washington 34 20 56
West Virginia 4 2 6
Wisconsin 40 0 40
Wyoming 2 1 3
American Samoa 0 0 0
Guam 1 1 2
Northern Marianas 0 0 0
Palau 0 0 0
Puerto Rico 8 1 9
Virgin Islands 0 0 2
Total 1,082 150 1,286*
pollution allowance
pollution allowance, government-issued permit to emit a certain amount of a pollutant; the holder of the permit may use it to pollute legally or may sell the permit for a profit. The allowance issued to a polluter is reduced over time as permitted levels of a pollutant are cut. By specifying reductions in emissions but leaving the polluter to decide how to cut them, the system is intended to provide incentives to lessen both pollution and compliance costs. A company that cuts its pollution below its permitted level may sell the surplus allowance; a company that exceeds its limits without purchasing an extra allowance is fined. Under the 1990 Clean Air Act, federal allowances for sulfur dioxide emissions are issued to polluters; additional allowances are auctioned.
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Earth Day, April 22, a day set aside to promote ecology, encourage respect for life on earth, and highlight the problem of pollution. First observed in 1970, Earth Day is now publicly celebrated worldwide.
Pollution from Cars
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Car’s are one of the main cause of air pollution.The gases from the exhaust pipes,weaken the layer that protect’s us from the sun’s harmful rays. The weking of this layer is called the ozone. The ozone affect stops harmful rays getting in to the earth. As shown in the diagam on the back page. This causes the poler ice caps to melt and this increse’s water levels.
Many people use there cars to go to work or to the coner shop. Many of these jouny’s are only a five minute walk away but a lot of people use car’s for short jouny’s and they don’t help so the carbon dioxide builds up and weken’s the ozone layer.
The cutting down of trees also afects pollution the trees take in carbon dioxide and give up oxygen. Becuse trees are being cut down more carbon dioxide is left in the air.
EVERY DAY THE OZONE LAYER
HOLE IS BEING MADE
BIGGER!!
The Boundless Sea
The seas are so vast that we have assumed that they will absorb all the rubbish we dump in them. In recent years, there have been more and more accidents involving oil spillage at sea. The sea has not been able to cope with it all. Accidents at oil rigs in the sea and at oil terminals, where tankers load and unload, many discharge oil into the sea. Some oil tankers flush out thier oil tanks at sea. This is illegal: they should do this in dock while delivering their oil. To do it at sea saves time, but itis a dreadful act of vandalism as it pollutes a vest area of sea.
Some of the oil evaporates, some dissolves, but most of it floats on the surface of the sea. Slowly, air oxidises it to cardon dioxide and water. Slowly, bacteria decompose it. But oil remains for a long time, and can do a lot of damage.
