58 



Nitrification of Sewage. 

 By Geokge Eeid, M.D., D.RH. 



(Communicated by Professor Gotch, F.E.S. Eeceived May 7, — Eead 

 November 1, 1906.) 



My special object in this paper is to direct attention to certain observations 

 I have recently made bearing upon depth of niters and grade of particles as 

 affecting both the quality of the work done and the capital outlay involved. 



To effect the necessary changes it is essential that the sewage in a fine film 

 shall be brought into intimate contact with the nitrifying organisms in the 

 presence of an adequate supply of oxygen. It follows, therefore, that the 

 larger the number of organisms employed, so long as they are maintained in 

 a healthy active condition, the greater the amount and the better the quality 

 of the work done. How then should a filter bed be constructed, so that, 

 within a given cubic space, it shall afford the largest possible surface non- 

 bacterial growth under healthy conditions ? Clearly, I suggest, by reducing 

 the particles composing the filter to the smallest size which is found to be 

 compatible with free aeration. 



Compare, from the point of view of effective working area, a filter formed 

 of 2-inch cubes — a grade in common use at present — with one formed of 

 -J-inch cubes, and it will be found that, bulk for bulk, the area in the latter 

 case is 16 times greater than in the former, but taking into account the 

 relatively larger space occupied by the smaller particles, the actual gain is as 

 1 to 147. 



The question is, then, to what extent in actual practice is it possible to 

 reduce the size of the filter particles ? Some four years ago I had an 

 opportunity of conducting an experiment on a large and practical scale at 

 Hanley with a plant which complied with all the conditions which previous 

 experience had shown me to be essential, including, for the first time I 

 believe, perfect and uniform distribution of the sewage on to the filter by 

 means of a power-driven apparatus. 



Shortly, this plant, which dealt with 500,000 gallons per day (1,000,000 

 gallons per acre), consisted of: — 



1. A detritus tank and strainer of the usual type. 



2. Three subsidence tanks having a total capacity equal to one-eighth the 

 daily dry weather flow. 



3. An open septic tank with a capacity of seven-eighths the daily flow 



