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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 



Fig. 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 lie 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 bird 



24—4966 



