186 



REPORT 1871. 



The amount of the preparation added to the sewage -was not ascertained, 

 but it was stated to be certainly much less than the proportion indicated by 

 previous experimeuts (1 ton of crude phosphate to 500,000 gallons of sewage). 



The result of this addition was to deodorize the sewage to a very consider- 

 able extent indeed ; and when some of it was placed in a precipitating glass, 

 and allowed to stand, a speedy separation of the suspended matters took 

 place. 



The milk of lime is added to precipitate the excess of phosphate added, 

 and just sufficient milk of lime is allowed to flow in to neutralize the sewage, 

 the reaction of which to test-paper is observed from time to time after the 

 addition of the milk of lime. 



During the passage of the sewage thus treated through the large tank, 

 the suspended matters were verj- completely deposited, and the supernatant 

 water ran over the sloping edge of the tank at its extreme end bright and 

 clear, and almost odourless. 



Some of this water was collected, and was kept sealed up in a stone jar 

 tin til July 24th, when it was analyzed by Dr. llussell, with the following 

 result : — 



Sample of Effluent Water taken from Tottenham Sewage, treated March 

 25th, 1871. Parts per 100,000. 



It was found, after the lapse of four m-onths, quite sweet and without 

 smell. The suspended matter was in very small quantity, and consisted 

 merely of a little whitish flocculent matter, doubtless lime due to the slight 

 excess used on the day when the sample was collected. The water was quite 

 clear, and only on looking through a considerable depth could a brownish 

 tint be detected. 



The analysis of it shows that it contains as much actual ammonia as 

 ordinary dilute London sewage, and also a certain amount of albumenoid 

 ammonia. 



It contains the merest trace of phosphoric acid, as indicated by the molyb- 

 date-of-ammonia test, and no sulphuretted hydrogen, nor any nitrates or 



nitrites. 



Some of the deposit had been taken out of the tank, and was drying in a 

 shed, the water which separated from it forming little pools on the surface of 

 the mass ; both this water and the precipitate itself were free from aU offen- 

 sive smell. 



It appears, then, that the suspended matters are entirely removed by this 

 process, but the actual ammonia and, to a certain extent, the soluble organic 

 matters are neither removed from the sewage nor oxidized ; but an odourless 

 precipitate is produced, which contains all the phosphate added, and contains 

 it doubtless in the form of flocculent phosphate of alumina, the value of 

 which, as a manure, is somewhat doubtful, being certainly not so great as 

 the value of corresponding quantities of flocculent phosphate of lime. 



The valuable constituents of sewage, with the exception of the suspended 

 matter and the phosphoric acid, are not precipitated by this process, and 

 cannot be utilized unless the effluent water be afterwards used for irrigation. 



