HIGH NITRIFICATION OF SEWAGE EFFLUENTS. 



467 



intervals, say once in twenty-four hours, and in that case may be taken 

 from a cesspool. The amount of attention required is practically nil, but 

 a few minutes should be devoted to it every morning to see that the 

 apparatus is working properly. 



Dealing now with the economic aspect of the apparatus, the results 

 obtained in continuous working over a period of many years are so high 

 as to place its value beyond all question. Sir Wm. Crookes, in his 

 presidential address to the British Association at Bristol in 1898, 

 estimated the loss arising from the wasted sewage of this country alone 

 at £16,000,000 per annum — a sum that would pay three per cent, on 

 a capital expenditure of £320,000,000 and still provide £6,400,000 per 

 annum for wages and depreciation. Seeing that ninety per cent, nitrifica- 

 tion of the total nitrogen in the effluents from ordinary sewage can be 

 obtained by the Ashtead apparatus, it follows that if the same conditions 

 could be applied to all the sewage of this country there would be a saving 

 of £14,000,000 out of the £16,000,000 referred to, with a margin for 

 gaseous losses as well. In these estimates it must be observed that 

 the nitrogen is not in a state that can be dealt with as an article of 

 commerce, seeing that it is diluted with enormous quantities of water, 

 which could only be conveyed in pipes to the points required. It is 

 therefore necessary to deal with the liquid form as we find it. 



The following is the standard solution adopted by Nobbe as a 

 model plant food supplied in parts per 100,000 : 



Lime .... 16*0 Chlorine . . . 21-0 



Magnesia . . . 3-0 Oxide of iron . . 0*5 



Potash . . . .31-0 Nitrogen ... 8-2 

 Phosphoric acid . . 7*0 



There is no doubt that all these substances are to be found in the 

 effluents from ordinary sewage ; but the most important of them, from 

 a manurial point of view, is the nitrogen. Upon comparing the results 

 from the Ashtead apparatus with these figures it will be seen that the 

 nitrogen obtained in an available form from the average of the eighth and 

 ninth trays, or 4 feet 3 inches of filtering depth, is 8*16 per 100,000, 

 which is almost identical with the figure given by Nobbe. 



Dr. Voelcker, in a letter to the late Mr. Pidgeon, speaks of this 

 solution as " containing those constituents, and the amount of each, 

 which have been found to be requisite for plant growth, and the absence 

 of any of which or the supply in markedly lesser quantity of which 

 would produce deterioration, while the larger supply of any of which 

 would not be attended by increased benefit." 



Turning now to the productiveness of small areas under highly 

 artificial conditions — a paper by Mr. Bear appeared in the Journal of the 

 Boyal Agricultural Society for 1889 in which he gives the return of 

 grapes at an average of 12 tons from the acre, or 14 tons from grapes in 

 full bearing, and tomatos at an average of 20 tons from the acre, both crops 

 to a great extent being grown on the same acreage. I have no figures 

 to show the cost of fertilizers required in order to produce these marvellous 

 results, which if generally realized would postpone the pressure of popula- 

 tion upon food supplies among civilized communities for an indefinite time ; 



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