SEWAGE DISPOSAL 305 



sewage directly into rivers which flow into the ocean. Conse- 

 quently, much of the liquid which bathes the shores of Manhattan 

 Island is dilute sewage. Other cities, like Buffalo or Cleveland, 

 send their sewage into the lakes from which they obtain their 

 supply of drinking water. The city of Chicago has built a huge 

 drainage canal which diverts water from Lake Michigan. Thus 

 the sewage is diluted and carried eventually into the Mississippi 

 River by way of the Illinois River. While there is not a noticeable 

 increase in the bacterial content of the Illinois River at the point 

 where it flows into the Mississippi, this drainage canal has done 

 harm in another way. The fish in the upper Illinois River have 

 been driven out or killed by the factory refuse and other wastes 

 which come down the canal. This is only one example of the 

 pollution of rivers by sewage and especially by factory wastes. All 

 over the eastern part of our country rivers have been made open 

 sewers, and now the conservation of our fish, as well as the water 

 supply of many of our cities, is becoming a serious problem. 



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This chart shows that during a cholera epidemic in 1892 there were hundreds 

 of cases of cholera in Hamburg, which used unfiltered water from the Elbe, but in 

 adjoining Altona, where filtered water was used, the cases were very few. 



The best way to avoid the pollution of rivers is by proper 

 sewage disposal, even if this method is expensive. Sewers for 

 large cities are planned so that the dilute sewage is carried to a 

 sewage disposal plant, usually situated a short distance outside 

 of the community. Here the solid wastes are screened out, and 

 then the smaller particles are precipitated out. The disposal of the 

 soUd material, called sludge, becomes a serious problem. London 

 and New York, each with millions of tons a year, dump their sludge 

 out at sea, where it becomes a nuisance to the people living on the 



