368 
The septic tank is usually a rectangular shaped chamber with several 
battle boards, extending across to break the flow of the sewage. Such 
tanks should be covered as the organisms that break down the solids 
(known as anaerobic bacteria) thrive best in the absence of air and light. 
Septic tanks usually take some time to become operative, a scum mat 
forming at the top and sludge at the bottom. At intervals such tanks must 
be cleaned of the sludge. It was formerly supposed that just as much 
solid matter was turned to liquid and gas to offset the amount of solids 
x 
Imhof{ Tank / Sexe ; : “y \ 0 
“. Sand Filler ite toe o YS v 
LAV PU E Sena sesto"y / ms, 
Sand Filler v.02. : / 
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Sand Fillers 
Chas Brossmann, Engineer ~~ 
Indianapolis 
Fic. 3. 
Imhoff Tank and Sand Filters Installed at Indianapolis Country Club 
coming in, however, it has usually been found necessary to clean out the 
resultant sludge at intervals. (See figure 1.) 
The Imhoff type of tank consists of two chambers, one for settling and 
one for the deposit and digestion of sludge. Such a tank, while somewhat 
more expensive than the plain tank is smaller and will give more uniform ~ 
results, besides offering better means for after-treatment of the liquid and 
assuring a better solution of the sludge problem. (See figure 4.) 
This type of tank has an upper settling chamber with a slotted opening 
at the bottom. The sewage in flowing through the upper chamber deposits 
