ANNIVERSARY ADDRESS. 31 



forward to the application of biological methods in dealing with 

 the sewage of Sydney, put the process into active operation at the 

 Botany Sewage farm, on an experimental scale, and at Rookwood 

 on a real working scale; plans and models of the system I have 

 now the pleasure of showing you to-night, through the kindness of 

 Mr. Smail, and of Mr. R. R. P. Hickson, the Under Secretary for 

 Public Works. As many other substances have been in use by 

 different observers for filling the sewage tanks, Mr. Smail used 

 ordinary sandstone and gravel from the Nepean River. At the 

 Botany Sewage Works an iron tank is used as an experimental 

 filter bed where the initiatory biological process is commenced. 

 This tank is provided with a false perforated bottom, upon which 

 the pebbles or stones rest, the tank being filled with crude 

 sewage and the fermentation process allowed to proceed for four 

 hours, the liquid then passes into the filters, of which there are 

 two — one filled with fragments of coke, the other charged with 

 small pieces of coal ; the tanks of coal and coke are so arranged 

 that either one may be used at will, thereby testing the relative 

 merits of each kind of material. The effluent is then run on to a 

 bed of lucerne and domestic vegetables, whereby the manurial 

 value can at once be estimated and practically put to use. One 

 thing is thus proved, that whereas crude sewage soon clogs the 

 land and renders the soil ' sewage sick,' the effluent acts at once 

 as a fertiliser, and a luxuriant crop of lucerne or vegetables is 

 produced. The cause is not far to seek, for the effluent is rich in 

 nitrates and ammonia, both compounds readily appropriated by 

 the growing crops. The crude sewage has the following com- 

 position on analysis. Mean of twenty-four samples taken every 

 hour, 18-19 April, 1900 :— 



Total solids 



Chlorine 



Free ammonia ... 



Albuminoid ammonia ... 



Oxygen absorbed in four hours 



Nitrous nitrogen 



Nitric nitrogen... 



56 



Parts per 



100,000 



12 



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