266 



SEWAGE AND ITS PURIFICATION 



Analysis of Septic Tank Contents taken on March 15, 1904. 



Albuminoid 

 Ammonia. 



Oxygen 

 Absorbed. 



Total Mineral 



Suspended Suspended 



Solids. Solids. 



0*665 



o'595 

 0-560 

 0*420 

 0*420 

 0-385 

 0-315 

 0-315 

 0315 

 0-315 



3*i6o 



2-673 



2-43 



2*43 



2-31 



1*944 



1*6 



1-6 



1-6 



1-6 



34*3 

 30*1 

 28*0 



25-9 

 22-4 

 21-0 

 20*3 



14-7 

 14-35 



»*4 

 8*4 



7-7 

 7-0 



63 



49 

 4 '9 

 4 '9 

 3-85 

 3*85 



Organic 



Suspended 



Solids. 



25-9 

 21*7 

 203 

 18-9 

 l6*I 



i6*i 



15-4 



12-6 



10-85 



io*5 



In septic tanks the sewage enters and emerges at practically 

 the same level, so that, for the first part of the process, no 

 pumping is required, nor difference of level necessary in the 

 land, as in most other processes. A certain time is, as usual, 

 required after a new installation for the bacteria to attain full 

 activity, but on account of the absence of interruption this 

 would appear to be short, especially if inoculated with scum 

 from an old active tank, after which the process goes on auto- 

 matically. Loss of capacity in the tank, due to collection of 

 solid matters, does not, unless in extreme cases, affect the 

 quantity of sewage which can be dealt with by it daily ; whereas 

 the loss of capacity in a bacteria bed does diminish the volume 

 of sewage which it can pass ; and in the event of cleansing 

 becoming necessary, the work of removing the deposit from 

 a septic tank is very light, compared with that which would 

 be required to wash the bed material of a bacteria bed of equal 

 working capacity. 



The principle of the septic tank is quiescence of the sludge 

 and removal only at long intervals. The following forms of 

 plant diverge from this idea, and approach to the old simple 

 sedimentation tank, which required frequent emptying and 

 produced large quantities of sludge. In Dunbar and Thumm's 

 trials at Hamburg the contents of the tank were drawn off 

 much too quickly on to the contact beds. 



The " Ames Tank," used at the Iowa State College at Ames, 

 is a semi-anaerobic arrangement in which the contents of the 

 receiving chamber are removed intermittently every 6 or 7 hours 

 instead of continuously, air being drawn in at each discharge, 

 whereby " escape is provided for the gases of decomposition 

 which have been found injurious to the purifying organisms of 



