And Pollution Control

3. Water pollution is considered to be perhaps an ever greater hazanj
to health and economic growth menace to recreation than air pollution. \
Millions of fish are killed in coastal waters and rivers each year. Radio­
active wastes detergents, pesticides, and other chemicals are found in
numerous rivers and streams. In addition, demands upon available wa­
ter 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.

Lesson 21 ^211

4. Pollution control. An over-all* reduction of the quantities of contam­
inants 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 l)iological processes.

5. 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.

6. Intensive research is needed to discover better and more efficient
techniques for treating water. Scientists in universities and research lab­
oratories 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.