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AMERICAN MUSEUM GUIDE LEAFLETS 



without emptying the liquid above. The ordinary shallow sedimentation 

 basin will not remove more than from 50 to 65 per cent of the suspended 

 solids, while the deep tanks at Birmingham effect a purification of 85 per 



cent. 



W here still more complete removal of suspended solids seems to he called 



for, the force of gravity may be reenforced by the addition of chemicals 

 which produce a flocculent precipitate, capable of carrying down with it 

 the finer particles, even to some of those which exist in a state of colloidal 

 suspension. This gives better purification but usually at a rather high com. 



THE SLUDGE PROBLEM 



In all processes of sedimentation a serious difficulty arises in connection 

 with the disposal of the semi-solid sludge removed from the sewage and 

 accumulated in the bottom of the basins. At the least there is produced 

 some five to ten tons of wet sludge (containing 90 per cent of moisture i 

 for every million gallons of sewage treated. For a community of one 

 hundred persons (assuming 100 gallons of sewage per capita) this would 

 mean one to two hundred pounds of wet sludge a day. With a village of 

 one hundred persons it would be easy to deal with this semi-solid waste 

 by burying it; but with a city of 100.000 inhabitants and 50 to 100 tons a 



DEEP SEDIMENTATION TANK 



A deep open i;mk for sedimentation or sewage. Photograph of a model in the \morican 



Museum 



