184 ANNUAL REPORT 



tem. The Worcester plant is to cost $300,000, and the annual ex- 

 pense of operating is placed at $22,000. 



In my judgment, there should be no delay on the part of our city 

 authorities in observing the results of these New England experi- 

 ments, and also of those in progress in Chicago and elsewhere, in 

 mechanical filtration. 



The ultimate disposal of sludge presents great difficulties, es- 

 pecially during our long and severe winters. It seems probable that 

 some plan of drying will have to be adopted. What one, can only be 

 decided after careful experimentation on the spot. 



The plans to be tried would seem to be these: 



1. Drying the whole sludge by means of filter presses, centrifu- 

 gals, blowers and perhaps artificial heat. 



2. Drying the whole sludge after mixture with dry earth. 



3. Drying only the organic stuff caught in precipitation tanks after 

 the subsidence of mineral matters in settling tanks. In cold weather 

 it might be found necessary to dry this earthy sludge in order to han- 

 dle it. 



As to the value of our sewage sludge for fertilizing, that, too, must 

 await the decision of experiment. Should the dry earth process of 

 defecation be adopted, the stuff can be used over and over until it 

 shall reach any desired degree of richness, and the sale of it would 

 help to pay expenses. If demanded by cultivators, it could be en- 

 riched by superphosphates or other chemical manures. It is at this 

 point that the co-operation of enterprising gardeners and fruit grow- 

 ers will be found indispensable. 



Let me briefly recapitulate : 



An inland city, like Minneapolis, has four kinds of filth to remove 

 and dispose of: 



1. Solid matter not excreta, such as sweepings, ashes, dirt, gar- 

 bage, rubbish, and stable litter. 



These must be collected, assorted and carted to convenient centres. 

 Garbage and rubbish and stable litter should be burned, except such 

 stuff as may be taken for manure. Other solids should be in demand 

 for fertilizing and filling low grounds. 



2. Rain water, to go ©ff by open gutters and into the common 

 sewers. 



3. Excreta. 



4. Foul water. 



These two to the sewers. 



Our four classes reduce then to two: 



