COLLECTION AND TREATMENT OF SEWAGE. 685 



2.— THE COLLECTION AND TKEATMENT OF SEWAGR. 

 By CHARLES E. BERXAYS. 



As it seems probable that definite steps will shortly hs taken to- 

 place Brisbane on the list of cities provided with a creditable sewage 

 system, a few notes on the subject should not be out of place. 



Here in Brisbane we are fortunately able to make a fair start> 

 unhampered by any existing system, so there is no reason for our not 

 adopting the most suitable and up-to-date methods or combination 

 of methods known to modern science. 



Before coming to the question of sewage collection, or treatment, 

 it must be remembered that our present -water supply is quite 

 inadequate for any system of sewage at all, and as the cost of 

 increasing it must be veiy great, any system of sewage collection 

 that requires a minimum amount of water for working or flushing- 

 purposes should receive special consideration from that point of view. 



Next to the water question comes that of outfall, and as the 

 cost of taking any form of sewage out into the ocean would be pro- 

 hibitive, whatever system of treatment is adopted it must be such 

 that the residue therefrom is quite harmless, and can be discharged 

 into the river or bay. 



In the older countries many systems of treatment are in vogue 

 with more or less satisfactory results; but for tropical and semi- 

 tropical lands the septic tank, wdien properly designed, has proved 

 to be quite satisfactoiy, and affords the cheapest and best method of 

 dealing with sewage. 



If septic tank treatment is decided upon for Brisbane, it 

 naturally follows that the method adopted for the collection should 

 bv? that which delivers the sewage in the best possible condition for 

 such treatment, and it is doubtful whether any person can be found 

 to argue that heavily diluted sewage is suitable for rapid and 

 efficient ti'eatment. This brings us to another point, and that is that 

 our sewers should not be used for the conveyance of storm water. It 

 may, of course, be contended that storm water supplies good flushing 

 water, and that cannot be disputed, but, on the other hand, during 

 heavy rains a gi'eat quantity of silt would be carried into the 

 system, and the sewers and tanks would have to be made larger at 

 veiy great expense, while during a flood no system could treat the 

 sewage, plus the flood water. We already have a good scheme for 

 dealing with our storm water, and that need not be disturbed. A 

 very great advantage gained by keeping the sewage free from storm 

 water is that the system would work equally well during flood time. 



The system most commonly in use for the collection of sewage 

 is that known as the '' Water Carriage." In these cases the system 

 consists of large main sewers, in brick and concrete, with earthen- 

 ware pipes as feeders. When sufficient fall cannot be obtained pump- 

 ing is resorted to, as in Sydney, Melbourne, and elsewhere. One 

 great objection to this system is the large quantity of water used for 

 flushing the sewers, which in our case would mean great expense for 

 water and much larger treatment tanks than would othenvise be 

 required. In nearly all places using water carriage the sewage is run 

 into the sea. 



