PURIFICATION OF WATER FOR DRINKING PURPOSES 200 



Bacterial purification of Sewage with Alum and Lime 



Scries A. 1,000 Ibs. of Alum and different amounts of Lime 



Number of 

 bacteria in 1 c.c. 



Original sewage . . , . , , . . . . . 835,200 

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

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



11 11 11 11 11 11 11 and 



400 Ibs. of lime. . 54,280 



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



600 Ibs. of lime 42,090 



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



800 Ibs. of lime 25,872 



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



1,000 Ibs. of lime 19,236 



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



2,000 Ibs. of lime 520 



Series B. Using different amounts 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 Ibs. of alum per million gallons of sewage . 11,160 



and 400 Ibs. of lime per million 



gallons of sewage ........ 92,250 



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



gallons of sewage 31,375 



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



sewage . . . . . . . . . . 63,750 



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



gallons of sewage ........ 7,900 



Effluent with 1,000 Ibs. of alum and 1,000 Ibs. 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 



