Introduction

nvironmental engineers and scientists have evolved as professionals over the past century to address human health and environmental problems resulting from industrial expansion, resource utilization, and the concentration of growing populations in cities. Such trends over the past two centuries have resulted in the biological and chemical contamination of water supplies, pollution of rivers, and severe fouling of air and land. To address these problems, environmental engineers have worked closely with scientists to learn new chemical, physical, and biological principles that can be applied to help solve these difficult human health and ecological problems.

For many years attention was devoted largely to the development of safe water supplies and the sanitary disposal of human wastes. Because of the success in controlling the spread of enteric diseases through the application of scientific and engineering principles, a new concept of the potentialities of preventive medicine was born. Expanding populations with resultant increased industrial operations, power production, and use of motor-driven vehicles, plus new industries based upon new technology have intensified old problems and created new ones in the fields of water supply, waste disposal, air pollution, and global environmental change. Many of these offer major challenges to environmental engineers and scientists.

Over the years, intensification of old problems and the introduction of new ones have led to basic changes in the philosophy of environmental protection. Originally the major objectives were to produce hygienically safe "water supplies and to dispose of wastes in a manner that.would prevent the development of nuisance conditions. Many other factors concerned with aesthetics, economics, recreation, and other elements of better living are important considerations and have become part of the responsibilities of the modem environmental engineer and scientist. If one were to develop a list of the most important environmental problems of today, it would include, but not be limited to, water and wastewater treatment, surface water and groundwater contamination, hazardous waste management, radioactive waste management, acid rain, air toxics emission, ozone depletion, and global climate change. Understanding these problems and development of processes to minimize or eliminate them requires a fundamental understanding of chemistry. ■

1.1 I WATER

Water is one of the materials required to sustain life and has long been suspected of being the source of much human illness. It was not until approximately 150 years ago that definite proof of disease transmission through water was established. For many years following, the major consideration was to produce adequate supplies that were hygienically safe. However, source waters (surface water and groundwater) have become increasingly contaminated due to increased industrial and agricultural activity. The public has been more exacting in its demands as time has passed, and today water engineers are expected to produce finished waters that are free of color, turbidity, taste, odor, nitrate, harmful metal ions, and a wide variety of organic chemicals such as pesticides and chlorinated solvents. Health problems associated with some of these chemicals include cancer, birth defects, central nervous system disorders, disruption of the endocrine system, and heart disease. At the present time, more than 85 specific chemicals are listed in the U.S. Environmental Protection Agency's drinking water standards, and the World Health Organization lists over 100 specific chemicals in its guidelines for drinking water quality. In addition, the public desires water that is low in hardness and total solids, noncorrosive, and non-scale-forming. To provide such water, chemists, biologists, and engineers must combine their efforts and talents. Chemists, through their knowledge of colloidal, physical, and organic chemistry, are especially helpful in solving problems related to the removal of color, turbidity, hardness, harmful metal ions, and organic compounds, and to the control of corrosion and scaling. The biologist is often of great help in taste and odor problems that derive from aquatic growths. In a true sense, therefore, all who cooperate in the effort regardless of discipline are environmental engineers.

As populations increase, the demand for water grows accordingly and at a much more rapid rate if the population growth is to be accompanied by improved living standards. The combination of these two factors is placing greater and greater stress on finding adequate supplies. In many cases inferior-quality, and often polluted, water supplies must be utilized to meet the demand. It is to be expected that this condition will continue and grow more complicated as long as population and industrial growth occurs. In many situations in water-short areas, purposeful recycling of treated wastewaters will be required in some degree to avoid serious curtailing of per-capita usage and industrial development. The ingenuity of scientists and engineers is being taxed to the limit to meet this need.

The problems faced by the water-supply community in developed countries are significantly different from those faced by underdeveloped countries. For example, in the United States many of the drinking water standards for organic chemicals are based on the desire to minimize the risk of developing cancer from drinking water containing suspected carcinogens. The level of acceptable risk is currently considered to be one-in-ten-thousand to one-in-a-million. That is, if one drinks water containing the chemical of interest at the level of the drinking water standard over a 70-year lifetime, the risk of developing cancer is increased by 10~4 to 10~6. Removing these compounds to these levels is a significant challenge. In the underdeveloped world, however, millions of children under the age of 5 die each year due to waterborne diseases. Thus, the goal of the water-supply engineer in this situation is significantly different.

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