148 ILLINOIS STATE ACADEMY OF SCIENCE 



80 to 100 gallons for smaller residential communities and 

 on np to 200 gallons per capita per day in some larger 

 cities. This flow is not uniform throughout the day but 

 rises and falls with the tide of human activities. 



The amount of organic matter which is present in sew- 

 age is relatively small. Some notion of the concentra- 

 tion can be gained by imagining the total daily bodily 

 wastes of one person plus his share of the industrial 

 wastes diluted with from 100 to 200 gallons of water. 

 Yet small as this amount of organic matter is, it must in 

 general be reduced by 70% to 95% before the sewage may 

 be discharged without offense. 



The number of urban districts in the United States 

 which have sewage treatment plants, or rather the num- 

 ber of those' which do not have such plants will, I think, 

 surprise you. Mr. Langdon Pearse, of the Sanitary Dis- 

 trict of Chicago, has compiled some interesting data in 

 this connection which appeared as a committee report to 

 the Society for Municipal Improvements. He states that 

 of 68 cities in the United States of 100,000 population or 

 over, including a total population of 27y 2 million, only 17 

 cities or a total population of 8% million have sewage 

 treatment works. In other words, less than one-third of 

 our larger cities treat their sewage. In the next group, in 

 cities of 25,000 to 100,000, with a total population of 

 10 1/3 million, only about 12 per cent have treatment 

 work. 



As in the case in most young industries, the importance 

 of technically trained operating personnel is not gener- 

 ally realized. The larger cities with treatment works em- 

 ploy a regular staff of chemists or at least a chemical 

 consultant employed intermittently. Of the 26 cities of 

 from 25,000 to 100,000 population with sewage plants, 

 only six employ trained operators, while in cities under 

 25,000 anybody from the Mayor to the dog catcher may 

 be detailed to look after the sewage works. This condi- 

 tion cannot long continue.' Sewage treatment is a com- 

 plex process and cannot be carried out successfully ex- 

 cept under the supervision of trained chemists. 



In discussing the manufacture of relatively pure water 

 from the combined water carried wastes of a modern citv 



