146 CREAMERY BUTTER* MAKING 



i. Purification of Sewage. The author, for several 

 years, has made efforts to gather the best information 

 concerning the purification of creamery sewage, a subject 

 which deserves the serious attention of every buttermaker 

 whose creamery is not so located as to permit a discharge 

 of the sewage into flowing water. 



These studies have recently been supplemented by care- 

 ful experimental tests, which have made it possible to 

 write the following discourse on sewage purification with 

 full confidence of the success of the method advocated 

 therein. 



The method of purification is the septic tank, <or germ 

 incubator. Some of the tanks now in use have worked 

 successfully; others have not. The author has seen and 

 examined both classes, with the satisfaction of knowing 

 that those that have not proven satisfactory are either too 

 small or imperfectly constructed. 



Principle of Septic Tank. With a thorough understand- 

 ing of the action of the septic tank, imperfections in its 

 construction are easily avoided. As seen in Fig. i, the 

 tank is so constructed as to retain all sediment and float- 

 ing material, since the discharges permit the withdrawal of 

 the liquid from near the middle of the tank only. This 

 is one of the main features of the tank. All inorganic 

 matter entering the tank will gradually settle, and, of 

 course, remain in it. The organic matter, especially the 

 casein, tends to settle during the first 24 hours,' after 

 which it comes to the surface to be gradually wasted 

 away by the action of bacteria. This wasting away is 

 naturally very slow, and since the slowly gathering or- 

 ganic matter nearly all remains in the first section of the 

 tank, this must be large enough to provide for a con- 

 siderable accumulation of it. One tank which was ex- 

 amined after operating for three months had not less than 



