369 
the solids into the sludge chamber below. In the sludge or digestion 
chamber below, the solids and organic matter is gasified and liquified inde- 
pendent of and without disturbing the settling matter above. 
The gases of decomposition and the constant agitation in the lower 
part does not disturb the sewage in the settling chamber, furthermore albu- 
men from the fresh sewage is not constantly added to the septic sludge; 
hence there is less odor and the sewage liquor is delivered in a fresher 
condition for after-treatment. The sludge from this type of tank dries out 
quicker, is in better condition for disposal, has less water content, and has 
different characteristics than sludge from a shallow tank which is kept in 
Fira. 4, 
Imhoff Tank, Julietta, Ind. Note Formation of Sludge on Sides. 
constant contact with the sewage. Such double tank sludge soon becomes 
spadable like garden compost. 
The tank treatment should be followed by dilution or some form of 
filtration. In some cases the sewage liquor from tanks can be discharged 
into a water-course. Usually it is necessary to use some form of filter or 
nitrification bed. This can be done in the following manner: 
(1) In small plants by discharging the sewage into tile laid near the 
surface of the ground. Such ground must be suitable for the sewage to 
percolate through to a subdrainage system below. Such ground should be 
gravely or of sand. (See figure 2.) 
(2) By discharging the sewage into contact beds, viz., a water-tight 
bed, filled to a depth of several feet with broken stone or other hard 
24—4966 
