46 MANAGEMENT OF DAIRY PLANTS 



an elbow on the inside of the tank so that the drainage will be 

 deUvered and take its exit below the surface of sewage already 

 in the tank, thus not disturbing the scum. 



The partitions, the elbows at the two ends, and the siphon 

 connections all operate to compel the liquid to run slowly 

 through the tank as desired and to keep the scum undisturbed. 

 As the drainage enters, the substances not in suspension — sohd 

 matter, sand, etc. — settle to the bottom, and leave the liquid 

 portion to be at once attacked by the numerous decomposing 

 ferments beneath the scum. 



The cover of the tank may be constructed from planks or 

 from concrete, the latter being the most satisfactory. It should 

 be provided with manholes through which the sediment in the 

 tank may be removed at least once a year. 



Dosing Chamber. — Farrington and Davis ' recommend that 

 a dosing chamber be provided between the septic tank and the 

 filter bed, its purpose being to compel the liquid from the tank 

 to discharge onto the filter bed intermittently instead of contin- 

 uously and thus allow air to permeate the filter bed at intervals. 



The dosing chamber should be large enough to contain eflSuent 

 from the tank sufficient to flood the filter bed from one to three 

 inches deep. The depth of the chamber should equal the dis- 

 charging depth of some standard siphon. 



Filter Bed. — This is constructed from about a foot of gravel 



on top of which is added three or four feet of coarse sand, tile 



being laid at the bottom of the gravel for carrying the water 



away. Farrington and Davis estimate that the area of the 



filter bed should be such that the rate of application of the settled 



wastes would not exceed 25,000 gallons per acre in 24 hours. 



r^, gallons of waste x 43,560 . ^,, , , . 



Thus, 2 i322_= area of filter needed, m 



25,000 



square feet. 



If the effluent has too strong an odor, they recommend that 



chloride of lime be added to it in the dosing chamber about an 



hour before its discharge onto the filter bed. The proportion 



' Wisconsin Exp. Sta. Bulletin 245, 1915, p. 13. 



