1906.] 



Nitrification of Sewage. 



65 



the whole of the sewage of the town. Before assenting to this proposal, 

 however, the authority decided to seek further advice, and this led to my 

 being consulted. 



Shortly, I may state that the experimental filter in this case had a mean 

 depth of 4 feet, and was formed of clinker broken to sizes varying from 

 J to \ inch, the sewage, after having undergone preliminary treatment, the 

 nature of which need not here be described, being distributed on to the filter 

 by means of a series of fixed sprays. The results obtained were fairly satis- 

 factory as regards nitrification, but the organic matter remaining uncon- 

 verted was considerable, and the effluent, so far as appearance went, was a 

 poor one, owing to the amount of suspended matter it contained. 



In order to determine whether and to what extent the imperfect results 

 were attributable to the comparatively large-sized medium composing the 

 filter, and with the view of ascertaining whether, in the case of the sewage 

 in question, a shallower filter would answer the purpose, I suggested that 

 a section of the filter should be partially reconstructed by removing the top 

 medium to a depth of 1 2 inches and replacing it by granite chippings broken 

 to g inch, and also that a collecting tray should be introduced at a depth of 

 3 feet in the reconstructed section. This alteration was made, and we 

 thus had the means of comparing the results obtained by the altered section 

 at depths of 3 feet and 4 feet 6 inches with those from the undisturbed section 

 at a depth of 4 feet 6 inches under identical conditions. 



Having resumed the working of the filter, at a rate of flow of 200 gallons 

 per square yard per day, three weeks were allowed to elapse for ripening 

 before the first set of samples were collected, and up to the time of writing 

 this paper the experiment, under the altered conditions, had been in 

 operation for four months. 



So far I have had an opportunity of analysing two sets of samples from 

 the two sections of the filter, and the following are the means of the more 

 significant results obtained : — 



Solids in suspension 



Free ammonia 



Albuminoid ammonia 



Oxygen absorbed in 4 hours at 80° F 

 Nitric nitrogen 



VOL. LXXIX. — B. 



Parts per 100,000. 



Septic 

 effluent. 



9-10 

 1-067 

 0-558 

 3-157 



Nil 



Unaltered 



section of 



filter at 



4 ft; 6 in. 



deep. 



2-10 



0-710 



0-154 



0-818 



1-04 



Altered 

 section of 



filter at 



4 ft. 6 in. 



deep. 



1-15 



0-250 



0-107 



0-680 



1-16 



Altered 

 section of 



filter at 

 3 ft. deep. 



1-00 



0-067 



0-044 



0-388 



2-58 



