NOTES ON THE PURIFICATION OF SEWAGE. 



XVII. 



After being in contact with the filters for varying periods the 

 following percentages of purification were obtained : — 



Percentage of improvement based on 



diminished quantity of albuminoid 



ammonia. 



Percentage of improvement based on 

 diminished amount of oxygen consiimed. 



Coal Filters. 



Coke Filters. 



Coal Filters. 



Coke Filters. 



82% 



82% 



63% 



65-5% 



After obtaining such satisfactory results from the sewage of the 

 Southern System, the Metropolitan Board decided to subject the 

 sewage of the Western System to a similar course of experiments 

 with the exception that in place of the septic tank, an installation 

 on the Scott-Moncrieff principle should be adopted, of sufficient 

 capacity to deal with sewage derived from 160 persons, allowing 

 them forty-two gallons per head per day. 



The tanks which were built in brickwork set in cement mortar 

 consist of one large cultivation tank and four contact filters, the 

 rate of flow being regulated so as to admit of eight hour cycles — 

 two hours filling, two hours standing full, two hours emptying, 

 and two hours aerating. The upward or cultivation tank was 

 provided with a false bottom, 12 inches from the floor, and con- 

 sisting of old railway iron built into the walls and bricks resting 

 on the flanges having two inch intervals. 



2- July, 17, isoi. 



