SEWAGE DISPOSAL 45 



liquefaction of protein, breaking up of milk sugars, and emulsi- 

 fication of fats. This generally necessitates a larger tank than 

 for a Uke amount of ordinary sewage. 



The size necessary to take care of this daily flow can be es- 

 timated in various ways, one being to assume that the amount 

 of sewage wiU be from itoiyi gallons for every pound of butter 

 manufactured. In general, a septic tank for creamery use 

 should be large enough to hold the sewage which would accumu- 

 late for about six days in the summer season. As fermentation 

 will be slower during winter, the sewage must be left longer in 

 the tank in order to decompose; but this is oflFset by the smaller 

 quantity of water used during winter months. Hence, one size 

 will usually prove satisfactory the year round. 



But before a septic tank is installed, the sewer from the build- 

 ing should be so connected that water which does not need 

 purification may be conducted away from the creamery without 

 passing through the septic tank, and only such drainage as needs 

 purification should be admitted to the tank; otherwise, the 

 sewage in the tank becomes too dilute and a much larger tank 

 will be required. Chemicals, such as strong acids or alkalies, 

 should be eUminated from sewage for the tank. 



Construction of Tank. — The septic tank should be so located 

 that its inlet is at least somewhat below the outlet from the 

 factory. The most satisfactory material for construction is 

 concrete. To facilitate decomposition, as explained above, the 

 tank should be divided into three compartments of equal size. 

 The outside walls and bottom should be about 12 inches thick; 

 the partitions may be reduced to 6 or 8 inches in thickness. 



Siphons connect the first compartment with the second and 

 the second with the third. They prevent the scum from being 

 carried away and thus destroying the putrefactive bacteria. 

 They also prevent the drainage from running across the surface 

 of the tank without remaining to be decomposed. These two 

 siphons, together with the inlet and outlet pipes, may be con- 

 structed from 4-inch pipe. 



The inlet pipe discharging sewage from the factory into the 

 tank and the outlet pipe at the opposite end should each have 



