ENVIRONMENTAL WORKS

infrastructure that provides cities and towns with water supply, waste disposal, and pollution control services. They include extensive networks of reservoirs, pipelines, treatment systems, pumping stations, and waste disposal facilities. These municipal works serve two important purposes: they protect human health and safeguard environmental quality. Treatment of drinking water helps to prevent the spread of waterborne diseases such as cholera, dysentery, and typhoid fever, and proper waste treatment and disposal practices prevent degradation of ecosystems and neighbourhoods. Similarly, cleaning the air of pollutant gases and particles as they are generated prevents adverse effects on both human health and the environment. Steady population growth, urbanization, and industrial development place steadily increasing demands on existing infrastructure, and these demands in turn create a need for the planning, design, and construction of new environmental works. Because the provision, operation, and maintenance of these works require a major investment of public funds, concerned citizens as well as municipal officials and decision makers should be familiar with the basic concepts of environmental works technology. This article presents an introduction to the fundamentals of environmental works. Its main focus is on the modern facilities and systems that provide communities with water, dispose of waste, and prevent pollution. Additional reading Broad coverage of water supply, waste disposal, pollution, and other public health and environmental sanitation topics may be found in Jerry A. Nathanson, Basic Environmental Technology (1986); Gilbert M. Masters, Introduction to Environmental Engineering and Science (1991); and Joseph A. Salvato, Environmental Engineering and Sanitation, 4th ed. (1992), including administrative aspects.Norman Smith, Man and Water (1975), presents a comprehensive history of water technology, including irrigation, hydropower, and drinking water. Mark J. Hammer, Water and Wastewater Technology, 2nd ed. (1986), an introductory engineering text, covers municipal water processing and distribution, wastewater collection and treatment, and sludge disposal. James C. Lamb III, Water Quality and Its Control (1985), provides a comprehensive but nontechnical introduction to water resources, including the basics of municipal water and wastewater systems, aquatic ecology, and water quality controls. Comprehensive, in-depth technical descriptions of the major desalting methods are found in K.S. Spiegler and A.D.K. Laird, Principles of Desalination, 2nd ed., 2 vol. (1980). James M. Montgomery Consulting Engineers, Inc., Water Treatment Principles and Design (1985), is a technical presentation of the physical, chemical, and microbiological principles of water purification, including process control, facilities design, and operational issues. Terence J. McGhee, Water Supply and Sewerage, 6th ed. (1991), presents sanitary engineering principles with emphasis on the design of water and sewage works. Warren Viessman, Jr., and Mark J. Hammer, Water Supply and Pollution Control, 5th ed. (1993), an engineering textbook, emphasizes the application of scientific principles to solving problems related to the movement and treatment of water and sewage. Warren Viessman, Jr., and Claire Welty, Water Management: Technology and Institutions (1985), presents the technical aspects of water resources systems as well as discussions of the related economic, political, and social problems. Metcalf & Eddy, Inc., Wastewater Engineering: Treatment, Disposal, Reuse, 3rd ed. rev. by George Tchobanoglous and Franklin L. Burton (1991), offers a detailed technical presentation of wastewater engineering principles and practices in a form suitable as a reference for professional engineers and as a textbook for engineering students.E.S. Savas, The Organization and Efficiency of Solid Waste Collection (1977), gives a thorough description of how cities organize, manage, and finance solid-waste collection services. George Tchobanoglous, Hilary Theisen, and Rolf Eliassen, Solid Wastes: Engineering Principles and Management Issues (1977), focuses on collection, transport, treatment, recovery, and disposal of residential and commercial solid wastes. C.L. Mantell (ed.), Solid Wastes: Origin, Collection, Processing, and Disposal (1975), offers technical discussion and case studies and includes the topics of agricultural and food-processing wastes, animal husbandry wastes, process industry wastes, and mineral and metallurgical wastes. David Gordon Wilson (ed.), Handbook of Solid Waste Management (1977), is a comprehensive source of data on the properties, handling, processing, and disposal of municipal solid waste, including information on resource reclamation and energy recovery. Amalendu Bagchi, Design, Construction, and Monitoring of Landfills, 2nd ed. (1994), provides in-depth coverage of modern landfill design, including site selection, leachate and gas control, operation, and economic analysis. Luis F. Diaz et al., Composting and Recycling Municipal Solid Waste (1993), thoroughly discusses municipal recycling facilities, waste composting operations, and integrated waste management concepts.J. William Haun, Guide to the Management of Hazardous Waste (1991), offers an introduction to the problems of hazardous-waste production, identification, treatment, and disposal and includes a discussion of laws and social issues. William C. Blackman, Jr., Basic Hazardous Waste Management (1993), is an introduction to hazardous-waste management methods and includes coverage of radioactive and infectious biomedical wastes. Michael D. LaGrega, Phillip L. Buckingham, and Jeffrey C. Evans, Hazardous Waste Management (1994), a professional reference and graduate-level engineering textbook, provides a comprehensive overview of hazardous-waste treatment, storage, disposal, site remediation, and management issues.Noel de Nevers, Air Pollution Control Engineering (1995), a university-level textbook, focuses on chemical engineering design applications and theory of air-pollution control equipment, effects of air pollution, air-pollution laws and regulations, meteorological factors, and atmospheric models. C. David Cooper and F.C. Alley, Air Pollution Control: A Design Approach, 2nd ed. (1994), covers equipment and technical details of process design for controlling particulates and gases, with an overview of air-pollution sources, effects, meteorological factors, and dispersion of pollutants. Howard E. Hesketh, Air Pollution Control: Traditional and Hazardous Pollutants, rev. ed. (1996), provides a technical and theoretical treatment of air-pollution control mechanisms and devices, with application data. Jerry A. Nathanson Air-pollution control Clean air, an essential component of a healthful environment, is a mixture of many different gases. Two gases predominate: nitrogen, which makes up 78 percent of the volume of clean dry air, and oxygen, which makes up 21 percent. Argon, an inert element, accounts for almost 1 percent of clean dry air, and the remainder includes very small or trace concentrations of carbon dioxide, methane, hydrogen, helium, ozone, and other gases. In the Earth's atmosphere, water vapour is also a significant component but the most variable one, ranging from 0.01 to 4 percent by volume; its concentration in air varies daily and seasonally, as well as geographically. Representative air-pollution control devices. Click on each image to see a detailed depiction. Air is considered to be polluted when it contains certain substances in concentrations high enough and for durations long enough to cause harm or undesirable effects. These include adverse effects on human health, property, and atmospheric visibility. The atmosphere is susceptible to pollution from natural sources as well as from human activities. Some natural phenomena, such as volcanic eruptions and forest fires, may have not only local and regional effects but also long-lasting global ones. Nevertheless, only pollution caused by human activities, such as industry and transportation, is subject to mitigation and control. Most air contaminants originate from combustion processes. In the Middle Ages the burning of coal for fuel caused recurrent air-pollution problems in London and in other large European cities. Beginning in the 19th century, in the wake of the Industrial Revolution, increasing use of fossil fuels intensified the severity and frequency of air-pollution episodes. The advent of mobile sources of air pollutioni.e., gasoline-powered highway vehicleshad a tremendous impact on air quality problems in cities. It was not until the middle of the 20th century, however, that meaningful and lasting attempts were made to regulate or limit emissions of air pollutants from stationary and mobile sources and to control air quality on both regional and local scales. The focus of air-pollution regulation in industrialized countries was initially on protecting ambient or outdoor air quality. This involved the control of a small number of specific criteria pollutants known to contribute to urban smog and chronic public health problems. Toward the end of the 20th century, the hazardous effects of trace amounts of many other air pollutants were recognized, and emission regulations were implemented. Long-term and far-reaching effects of certain substances on atmospheric chemistry and climate were also observed at that time, and cooperative international efforts were begun to mitigate their global effects. Types, sources, and effects of air pollutants There are six traditional criteria pollutants. They include fine particulates, carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, and lead. Except for lead, criteria pollutants are emitted in industrialized countries at very high rates, typically measured in millions of tons per year. All except ozone are discharged directly into the atmosphere from a wide variety of sources. They are regulated primarily by establishing ambient air quality standards, which are maximum acceptable concentrations of each criteria pollutant in the atmosphere, regardless of their origin. Hazardous air pollutants are emitted in smaller amounts than are the criteria pollutants, usually from specific industrial activities. They are regulated primarily by emission standards, which are maximum allowable rates at which each air pollutant can be discharged from a particular source. Although the total emissions and the number of sources of these pollutants are small compared with those for criteria pollutants, hazardous air pollutants can pose an immediate health risk to exposed individuals and can cause other environmental problems. Hazardous-waste management Hazardous waste is any waste material that, when improperly handled, can cause substantial harm to human health and safety or to the environment. Hazardous wastes can take the form of solids, liquids, sludges, or contained gases, and they are generated primarily by chemical production, manufacturing, and other industrial activities. They may cause damage during inadequate storage, transportation, treatment, or disposal operations. Improper waste storage or disposal frequently contaminates surface and groundwater supplies. People living in homes built near old and abandoned waste disposal sites may be in a particularly vulnerable position. In an effort to remedy existing problems and to prevent future harm from hazardous wastes, governments closely regulate the practice of hazardous-waste management. Hazardous-waste characteristics Hazardous wastes are classified on the basis of their biological, chemical, and physical properties. These properties generate materials that are either toxic, reactive, ignitable, corrosive, infectious, or radioactive. Toxic wastes are poisons, even in very small or trace amounts. They may have acute effects, causing death or violent illness, or they may have chronic effects, slowly causing irreparable harm. Some are carcinogenic, causing cancer after many years of exposure. Others are mutagenic, causing major biological changes in the offspring of exposed humans and wildlife. Reactive wastes are chemically unstable and react violently with air or water. They cause explosions or form toxic vapours. Ignitable wastes burn at relatively low temperatures and may cause an immediate fire hazard. Corrosive wastes include strong acidic or alkaline substances. They destroy solid material and living tissue upon contact, by chemical reaction. Infectious wastes include used bandages, hypodermic needles, and other materials from hospitals or biological research facilities. Radioactive wastes emit ionizing energy that can harm living organisms. Because some radioactive materials can persist in the environment for many thousands of years before fully decaying, there is much concern over the control of these wastes. However, the handling and disposal of radioactive material is not a responsibility of local municipal government. Owing to the scope and complexity of the problem, the management of radioactive waste (particularly nuclear fission waste) is usually considered to be a separate engineering task from other forms of hazardous-waste management and is discussed separately in nuclear reactor. Solid-waste management Material that is discarded because it has served its purpose or is no longer useful is called solid waste. Improper disposal of municipal solid waste can create unsanitary conditions, and these conditions in turn can lead to pollution of the environment and to outbreaks of vector-borne disease (that is, diseases spread by rodents and insects). The tasks of collecting, treating, and disposing of solid waste present complex technical challenges. They also pose a wide variety of administrative, economic, and social problems that must be managed and solved. Historical background Early waste disposal In ancient cities wastes were thrown into the unpaved streets and roadways, where they were left to accumulate. It was not until 320 BC, in Athens, that the first known law forbidding this practice was established. At that time a system for waste removal began to evolve in Greece and in the Greek-dominated cities of the eastern Mediterranean. In ancient Rome property owners were responsible for cleaning the streets fronting their property. But organized waste collection was associated only with state-sponsored events, such as parades. Disposal methods were very crude, involving open pits located just outside the city walls. As populations increased, efforts were made to transport waste farther out from the cities. After the fall of Rome, waste collection and municipal sanitation began a decline that lasted throughout the Middle Ages. Near the end of the 14th century, scavengers were given the task of carting waste to dumps outside city walls. But this was not the case in smaller towns, where most people still threw waste into the streets. It was not until 1714 that every city in England was required to have an official scavenger. Toward the end of the 18th century in America, municipal collection of garbage was begun in Boston, New York City, and Philadelphia. Waste disposal methods were still very crude, however. Garbage collected in Philadelphia, for example, was simply dumped into the Delaware River downstream from the city. Water-pollution control Water is called the universal solvent because of its strong tendency to dissolve other substances. Since pure water is not found in nature (i.e., outside chemical laboratories), any distinction between clean water and polluted water depends on the type and concentration of impurities found in the water as well as on its intended use. In broad terms, water is said to be polluted when it contains enough impurities to make it unfit for a particular use, such as drinking, swimming, or fishing. Although water quality is affected by natural conditions, the word pollution usually implies human activity as the source of contamination. Water pollution is caused primarily by the drainage of contaminated waters into surface water or groundwater. Water-pollution control, therefore, primarily involves the removal of impurities before they reach natural bodies of water or aquifers. Historical background Direct discharge of sewage Many ancient cities had drainage systems, but they were primarily intended to carry rainwater away from roofs and pavements. A notable example is the drainage system of ancient Rome. It included many surface conduits that were connected to a large vaulted channel, called the Cloaca Maxima (Great Sewer), which carried drainage water to the Tiber River. Built of stone and on a grand scale, the Cloaca Maxima is one of the oldest existing monuments of Roman engineering. There was little progress in urban drainage or sewerage during the Middle Ages. Privy vaults and cesspools were used, but most wastes were simply dumped into gutters to be flushed through the drains by floods. Toilets (water closets) were installed in houses in the early 19th century, but they were usually connected to cesspools, not to sewers. In densely populated areas, local conditions soon became intolerable because the cesspools were seldom emptied and frequently overflowed. The threat to public health became apparent. In England in the middle of the 19th century, outbreaks of cholera were traced directly to well-water supplies contaminated with human waste from privy vaults and cesspools. It soon became necessary for all water closets in the larger towns to be connected directly to the storm sewers. This transferred sewage from the ground near houses to nearby bodies of water. Thus, a new problem emerged: surface water pollution.