BACTERIAL PURIFICATION 209 



settled — (i) how the sewage of cities could be purified by 

 )acteria where large tracts of sandy soil did not occur ; (2) how 

 :he large amount of suspended matter, like paper, w^ool waste, 

 Lud the other various forms of cellulose not easily acted upon 

 )y bacteria, could be prevented from forming a layer over, and 

 ^logging up the sand ; (3) whether sewage containing large 

 tmounts of manufacturing waste, especially free acid and iron 

 Its, could be treated bacterially. The Massachusetts inter- 

 littent filtration could treat with permanent success not more 

 than 100,000 gallons per day per acre, much too limited a 

 rolume for towns and cities which would be obliged to con- 

 struct beds with sand not in situ. This point was quickly 

 )erceived in England, where such sand is not of common 

 occurrence, and the bacterial sewage work in England started 

 ^ith the problem : Can the amount of land required by the 

 itermittent filtration method be so reduced that the construc- 

 [ion of artificial bacteria beds will be a practical possibility ?^ 



The sewage of Lawrence City, in the Massachusetts in- 



restigation, had been run on the filters without any previous 



purification, or even settlement. On the other hand, the 



jwage of London had been previously treated with i grain per 



gallon of ferrous sulphate and 4 grains of lime, the precipitated 



sludge being then conveyed in boats to be discharged at the 



mouth of the Thames. It was hoped that the clarified liquid 



could be discharged into the river direct without creating 



nuisance. But it still contained about 7 grains per gallon of 



suspended solids, and was by no means free from odour. The 



Royal Commissioners of 1884 had decided that the liquid 



could not be discharged at the outfalls as a permanent measure, 



and required further purification by application to land. 



In 1866 an experiment with London sewage as applied to 

 land had already been made at Barking. The Metropolis 

 Sewage Company obtained a concession to treat the sewage of 

 North London, amounting to about 2,000 tons in nine or ten 

 hours, on 5 or 6 acres of grass land on a light gravelly soil. 

 The experiment was not a success, either culturally or with 

 regard to the cleansing of the effluent. But with the 

 200,000,000 gallons daily of London sewage, it was recognised 

 that the requisite area of suitable land is entirely unattainable. 



^ Fuller has calculated the average composition and volume per capita of the 

 sewage of several English cities from published records, 1898 to 1902. — Technology 

 Quarterly, June, 1903. Also see R. Commission on Sewage, vol. iii., 1902. 



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