2l8 



SEWAGE AND ITS PURIFICATION 



The average results in his table (p. 217) I have calculated, 

 for the purpose of comparison, to a uniform chlorine content 

 of 12*84 parts, the average given for the Sutton crude sewage. 



These figures show the following percentages of purification : 



Oxygen 



absorbed. 



By the " bacterial tank " ! 

 By the coke filter 

 Total purification 



53 

 29 

 82 



FreeNH-j. 



69 



Albuminoid 

 NH3. 



90 



47 



25 

 I 72 



Suspended 

 Matter. 



94 



4*4 

 98-4 



It will be observed that the chief purification occurs in the 

 *' bacterial tank," and that a large proportion of it consists in 

 the removal of the suspended solids. 



Fig. 21. — Contact, or "Dibdin" Filters on Dual System at Sutton. 



During the two hours of resting full, a mixture of organisms, 

 of which I believe a great proportion are anaerobic, as indicated 

 by the large production of nitrites, are liquefying the sludge. 

 It was estimated that in the three tanks 80 tons of dry matter 

 had been thus reduced from November, 1896, to December, 1897. 

 During the period of resting empty, the aerobic bacteria, are 

 supposed to be at work, although, according to Mr. Dibdin, no 

 air enters except that drawn in while emptying out the liquid. 

 The subsequent coke-breeze filter is intended, under the same 

 conditions, to be entirely aerobic and nitrifying. The Second 

 Report of the Royal Commission on Sewage, 1902, No. 2, 



