The Problem of Water Pollution and Pollution ControlWater pollution means contamination of surface or ground water1 supplies by sewage industrial wastes or garbage and other refuse. Water pollution arises from the activities of man in his cities, industries and agricultural pursuits. Water pollution becomes not only an esthetic problem for man, but an economic and medical one as well. Bacterial and viral contamination is a threat for the spread of waterborne diseases such as typhoid, shigellosis or bacillary dysentery, amoebic dysentery, cholera and hepatitis. Water pollution is considered to be perhaps an ever greater hazard to health and economic growth menace to recreation than air pollution. Millions offish are killed in coastal waters and rivers each year. Radioactive wastes detergents, pesticides, and other chemicals are found in numerous rivers and streams. In addition, demands upon available water have multiplied because of a larger population, concentrations of people in large urban areas, higher standards of living, growing industry, increased agriculture, and the production of new chemical substances requiring water in the manufacturing process. Pollution control. An over-all reduction of the quantities of contaminants to be discharged to watercourses is necessary. The users of public waters have a responsibility for returning them as clean as possible. Adoption of better industrial and agricultural practices will be necessary to prevent the more toxic wastes from being discharged into lake, stream, or ocean. For the majority of wastes from cities and industries the solution lies in treatment by physical, chemical, and biological processes which will remove suspended, colloidal and dissolved solids. Sedimentation, coagulation and filtration will remove up to 50% of the organic matter. For more thorough removals it is necessary to use biological processes in which large masses of bacteria and other microorganisms are brought into close contact with the soluble and colloidal organic matter in the waste waters. «Biological filters» are used in most of the biological processes. Prevention of pollution. Waters generally are classified as surface waters and ground waters. Surface waters are lakes, rivers, reservoirs, streams and costal waters. Treating polluted surface waters is somewhat simpler than eliminating pollution from ground waters, where the pollution can travel rapidly or slowly depending on the nature of the ground strata through which the supply moves and on the nature of the pollution itself. Intensive research is needed to discover better and more efficient techniques for treating water. Scientists in universities and research laboratories are studying a very wide range of renovation techniques. Among them are absorption by carbon or other absorptive filters, distillation, foaming, freezing, ion exchange, solvent extraction, electrodialysis and electrolysis. Notes 1. surface waters поверхностные воды; ground waters грунтовые воды Упражнение 1. Просмотрите текст. Назовите факторы, приводящие к загрязнению природных вод, и способы борьбы с ними и зависимости от типа загрязнения.
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