Municipal sewage is of relatively recent origin as a pollutant. It was first brought to public attention in the 19th century by a London physician who showed that the city’s cholera outbreak had been caused by just one contaminated well. Even though the contamination of drinking water by disease germs has been nearly eliminated in this country, hundreds of communities are still discharging raw sewage into streams and rivers.
The problem of municipal sewage disposal is complicated by the fact that, years ago, most cities combined their storm and waste disposal sewers. Many of these combined systems work well, but others cannot cope with sudden heavy rains. When such storms occur, water mixed with sewage may flood and disable treatment plants unless bypassed, untreated, into a stream. In either case, the people may have little protection for several days from these wastes that may contain disease germs.
One consequence of pollution, usually resulting from the discharge of either raw or treated sewage wastes into water sources, is an increase in nutrient levels in these waters. These higher nutrient levels result in a rapid increase in the biological population of the water. Excessive respiration and decomposition of aquatic plants deplete the oxygen content in these waters causing decay which, in turn, may produce an undesirable taste, odor, color and turbidity. Increasing nutrient contents may also result in an in- crease in more undesirable species of aquatic life. All these factors make the water un- fit for domestic, industrial and recreational purposes.