784 PROCEEDINGS OF SECTION M. 



scheme would be £98,500, against £53,380 for the precipi- 

 tation one, — a difference of over £45,000 a year in favour of 

 the latter. 



Nor is this all. As I have before remarked, the method of 

 sewage disposal affects the methods of its collection. At 

 Melbourne the necessity of having a single pumping station 

 for the eastern outfall involved the necessity of having 

 enormously large and very deep collector main sewers 

 leading to it. If these sewers could discharge, after preci- 

 pitation treatment, at any convenient outlet on the Yarra 

 and other streams (and provision is made for this in the 

 other scheme), it is manifest that these sewers could be 

 greatly reduced in size and in depth, and probably half, and 

 certainly a third, of their cost could be saved. This would 

 make the total cost of the irrigation scheme £2,670,000, 

 being more than two millions in excess of the other ; and 

 the yearly expenses £125,000, being nearly £72,000 a year 

 more than the precipitation scheme. 



So much for the economical aspect of the two systems. 

 If we consider another aspect — the hygienic — we shall find 

 the advantages are also on the side of the precipitation 

 scheme. I have already pointed out the dangers arising 

 from allowing sewage time to ferment while slowly flowing 

 through immense sewers laid at flat gradients. And when 

 the sewage arrived at the farm, it would have to be 

 differently managed than any sewage farm I ever saw — and 

 I have seen a great number — if the irrigation did not create 

 some nuisance. But with the precipitation system no 

 nuisance need arise anywhere. The sewage would quickly 

 arrive — and consequently ari-ive while quite fresh — at the 

 mixing-tanks, where it would be rendered, practically 

 speaking, imputrescible. The mud precipitated need not be 

 exposed nor touched until it forms part of the chnker drawn 

 from the furnaces. 



Again, with regard to the cai'rying out and practical 

 working of the two systems, the advantages are all in favour 

 of a precipitation scheme with several outfalls. In the first 

 place, it has a capacity of adaptation that the irrigation 

 scheme has not. For instance, if on the morrow of the 

 completion of some such collection system as I have roughly 

 sketched out, the electrolytic system were so far perfected as 

 to render its adoption desirable, every part of the work done 

 would be immediately available : and so with other systems 

 of treatment. Take even the extreme case of having after 



