l*REStDENT's ADDRESS — SECTION H. 165 



fiver. The sewage from two millions of people is discharged 

 into New York Harbour, but the volume and velocity of tidal 

 water is exceptionally great and the result fairly satisfactory. 

 At Brighton, England, and at several other seaside towns, 

 the outlets have proved unsatisfactory because of the return 

 of the sewage on to the beaches, so that very expensive con- 

 duits for removal to suitable distances have become neces- 

 sary. The sewerage of the Northern section of Sydney 

 discharges into the ocean in deep water, and there is no 

 nuisance, or prospect of a nuisance, from this method of 

 disposal. 



Chemical Precipitation Processes have been applied to 

 render the effluent sufficienly pure to discharge into a river, 

 but these are only jjartial, as they leave the precipitated 

 impurities known as sludge to be dealt with in some otiier 

 way. The purification of the effluent is more ajjparent than 

 real, and it rapidly decomposes if allowed to remain stagnant. 

 The sewage is collected in tanks, and lime, salts of iron, 

 alumina, or other coagulating or precipitating agents are 

 added, Avhich precipitate the suspended and some of the 

 dissolved matters as sewage sludge. The sludge conlains 

 about 90 per cent, of water, and in the case of the London 

 sewage it is pumped out of special settling tanks into sludge 

 barges and discharged under water far from land. The 

 clear effluent is discharged into the Thames some miles down 

 the river. Sludge may be dried to reduce its bulk, or com- 

 pletely destroyed by fire in a specially constructed furnace. 

 Or, again, it may be pressed so as to reduce its bulk and 

 render it more easily conveyed by cartage. It has about 

 l-7th of the value of ordinary sewage as a manure, and may 

 be dug into the ground on a farm. In any case it must be 

 specially dealt with, as it becomes very offensive. Chemical 

 processes can hai'dly be considered satisfactory. 



In inland towns, and wherever the expense of dis- 

 charging the sewage out to sea is greater than that of 

 disposing of it on a sewage farm, the latter should be 

 adopted. A sewage farm, if properly managed, will do 

 something more than pay working expenses, and it is a most 

 satisfactory method, from a sanitary point of view, for the 

 disposal of sewage. A large number of sewage farms exist 

 in various parts of the world, and the results are uniformly 

 satisfactory. There are two methods (which are largely 

 used) of applying sewage to land : — a. Broad Surface Irriga- 

 tion ; J, Intermittent Downward Filtration. A third method. 



