PURIFICATION OF WATEK FOR DRINKING PURPOSES 209 



Bacterial ptirification of Setvage with Alum and Lime 



Series A. — 1,000 lbs. of Alum mid different amounts of Lvtne 



Number of 

 bacteria in i c.c. 



Original sewage ... 835,200 



Ditto after settling 1 hour without additions .... 994,500 

 Effluent with 1,000 lbs. of alum per million gallons of sewage . 7,200 



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400 lbs. of lime 54,280 



Efdtient with 1,000 lbs. of alum per million gallons of sewage and 



600 lbs. of lime 42,090 



Effluent with 1,000 lbs. of alum per million gallons of sewage and 



800 lbs. of lime 25,872 



Effluent with 1,000 lbs. of alum per million gallons of sewage and 



1,000 lbs. of lime 19,236 



Effluent with 1,000 lbs. of alimi per million gallons of sewage and 



2,000 lbs, of lime 520 



Series B. — Using different amoicnts of Alum and Lime 



Number of 

 bacteria in 1 c.c. 



Original sewage ... 361,328 



Ditto after settling 1 hour without additions .... 347,600 

 Effluent with 500 lbs. of alum per million gallons of sewage . 11,160 



„ „ „ and 400 lbs. of lime per million 



gallons of sewage 92,250 



Effluent with 500 lbs. of alum and 800 lbs. of lime per million 



gallons of sewage . . 31,375 



Effluent with 1,000 lbs. of alum alone per million gallons of 



sewage 63,750 



Effluent with 1,000 lbs. of alum and 500 lbs. of lime per million 



gallons of sewage 7,900 



Effluent with 1,000 lbs. of alum ^nd 1,000 lbs. of lime per million 



gallons of sewage 4,760 



The above tables show that a particular proportion 

 of lime, depending of course on the nature of the sew- 

 age, gives as good or a better result than either more 

 or less ; and again that, speaking generally, the more 

 copperas, the more ferric sulphate, and the more alum 

 employed, the better is the result achieved. Moreover, 

 whilst ferric sulphate and alum usually require no 

 lime for complete precipitation, the latter is only 



p 



