365 
SEWAGE DISPOSAL. 
CHARLES BROSSMANN, Consulting Engineer, Indianapolis. 
Civilization and education has been accompanied by a wondertui 
erowth of cities and has made the problem of sewage disposal one of civic, 
state and national importance. 
Sanitation becomes of greater importance as communities become 
more congested. 
It is only of late years that this question has received proper atten- 
tion, the greatest progress having been made in the last few decades. ‘Lhe 
combined efforts of the scientist, chemist and engineer have been Called 
upon to help solve this problem of ever-increasing importance. 
Improper disposal of sewage has caused directly or indirectly a large 
percentage in the typhoid mortality rate. 
The gathering of large numbers of people calls for additional safe- 
guards and means of sanitation. In some instances sewage can be dis- 
posed of by dilution, discharging direct into large bodies of running water: 
but most streams are as a rule not of sufficient size, or are already so 
polluted that additional sewage would increase the burden already too 
large. 
Generally sewage is diluted with the entire water supply of a city and 
is a dirty appearing water, containing a greater or less percentage of 
organic matter. There is usually enough organic matter present to make 
it disagreeable and to cause odors. The presence of various disease germs 
also make it a source of pollution to water bodies. 
In general all methods of sewage treatment employ the principal of 
reduction through microscopic organisms. Bacteria of various kinds at- 
tack the organic compounds reducing them to simpler forms, doing so 
through successive stages. Reduction takes place through two classes of 
bacteria, hamely aerobic (thriving in the presence of oxygen), and anae- 
robic (thriving in the absence of oxygen). These two processes occur in 
septic, Imhoff or other tanks and in yarious forms of filters. 
The most prevalent form of getting rid of sewage is by dilution. 
Where the stream is sufficient in size to allow proper oxidation the sewage 
