XVI. J. G. S. PURVIS. 



renders it prohibitive, and the disposal of the sludge is an intoler- 

 able nuisance. 



This then appears to have been the position of the sewage 

 question in Sydney and suburbs within very recent years, although 

 prior to this the subject of bacterial purification or disposal of 

 sewage had arrested the attention of the Engineer to the Metro- 

 politan Board. Certain well defined principles are already 

 recognised and generally accepted, nevertheless the following 

 processes and operations are quite old in application in the field 

 of sewage disposal. (1) Sedimentation. (2) Reduction or 

 liquefaction of the solids by anaerobic bacteria. (3) Submerged 

 inlets and outlets to cultivation tanks. (4) Exclusion of light 

 and air. (5) Artificial ventilation. (6) Discharge over weirs or 

 cascades for the purpose of aeration. (7) Periods of contact with 

 filtering material, rest and recuperation — which is simply the old 

 system of intermittent downward filtration adopted on most 

 sewage farms. This being so, there is nothing novel in the action 

 which is produced in the modern filter or septic tank, but there 

 certainly is in some of the gears or devices which have been 

 designed for the purpose of controlling the distribution of the 

 sewage. 



In 1898 the Metropolitan Board decided to carry out a series 

 of experiments on a small scale, in order to ascertain whether the 

 sewage delivered on the farm by the Southern System would be 

 amenable to treatment by the septic process. The tanks were 

 simply wrought iron tanks of four hundred gallons capacity, and 

 two different processes were adopted, viz.: — the septic tank and 

 the Scott-Moncrieff systems. After a very carefully conducted 

 series of analyses by Mr. Doherty of the Board of Health, the 

 following average results were obtained : — 

 Raw Sewage — 

 Total solids ... ... ... 657 parts per million 



Chlorine 120 „ 



Free ammonia ... ... ... 43 ,, 



Albuminoid ammonia ... ... 25 ,, 



Oxygen absorbed in four hours... 64 ,, 



