37° Report S.A.A. Advancement of Science. 



The Septic tank is one through which the sewage is allowed to 

 flow at a slow rate so that the suspended matter in the sewage sinks 

 to the bottom of the tank where a certain percentage of it is, in time, 

 either liquefied or changed into gaseous products, thereby reducing 

 the amount of sludge which has ultimately to be dealt with, while at 

 the same time a bacterial action or fermentation is set up in the tank 

 and we have a self-purifying process or " working " of the sewage. 

 The result is a liquid from which has been removed a large percentage 

 nf the solid matter in susp>ension and a smaller percentage of solids 

 in solution. Just how much of these solids are removed depends on 

 such conditions as the strength and condition of the sewage, the 

 general temperature and the rate of flow through the tank, under 

 favourable conditions the amount of sludge decomposed appears to 

 be from 26 to 30 per cent, of the total suspended matter arrested in 

 the tank. 



During the past five or six years the Septic tank has been installed 

 in a great many places and while it cannot be considered a complete 

 solution of the sewage purification problem it has come to be looked 

 upon as an essential first stage in the l)acterial treatment of sewage, 

 and in one form or another now takes its place in all sewage disposal 

 works. 



" Contact Beds " are filters of porous material in which the 

 sewage is allowed to rest for a certain length of time in contact with 

 the nitrifying bacteria which form in the filter and which by their 

 life process effect a chemical change in the sewage by which it is 

 purified. The essential principle of the beds is that a certain amount 

 of time should be given between each filling of the beds to allow them 

 10 thoroughly aerate in order t(j sui:)ply the organisms with the 

 atmospheric oxygen which enables them to perform their work. 



Beds on this principle have i)een extensively used in various 

 parts of the world during the past few years Avith success. The 

 percentage of purification effected by them depends largely upon the 

 regularity in which the periods of filling, standing full, emptying and 

 standing empty or aerating is maintained. These contact beds were 

 originally used for treating crude sewage but are now used in conjunc- 

 tion with septic tanks and it is generally conceded that sewage after 

 having undergone preliminary treatment by the septic tank process 

 can be purified by contact beds so as not to undergo secondary pu- 

 trefaction at the rate of 500,000 to 1.000,000 gallons per acre per 

 diem. 



The system that for want of a better title is known as the " Inter- 

 mittent continuous filtration " method to distinguish it from continuous 

 liltration efl'ects the purification of sewage by the same process as the 

 Contact Beds, the difference in the action of this method being that 

 instead of allowing the sewage to remain in the filter in contact with 

 the nitrifying bacteria for a length of time it is passed through the 

 filter in a thin continuous stream, the supply of atmospheric oxvgen 

 that is necessary to enable the bacteria to perform their function be- 

 ing attained by special construction of the filter and by the means 



