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DISPOSITION OF SLUDGE. 
The real problem in sewage disposal plants is the sludge problem. En- 
gineers are just learning how to make sludge but in most cases have not 
found a satisfactory solution in disposing of it. In larger plants the sludge 
question is the stumbling block. 
Sludge may be roughly divided in two classes, that from shallow tanks 
and that from deep tanks. Sedimentation tank sludge is a black semi- 
Fie. 6. 
Sand Filters, Julietta, Ind. 
liquid mass which on being exposed to the air becomes offensive, giving off 
much gas and odor. The water contained from such sludge is usually 90 
to 95%. 
The sludge from septic tanks ranges all the way from 8 to 45 cubic 
yards per million gallons of sewage. Septic sludge which has been re- 
tained in tanks for a number of months undergoes a great change. The 
organic matter is attacked and partly gasified and liquified, which re- 
duces the amount of sludge. Such sludge in well operated tanks is a con- 
