1906.] Nitrification of Sewage. 67 



filtering material used was coke of practically the same grade as that used at 

 Hanley, and the sewage was delivered on to the niters at the rate of 

 300 gallons per 24 hours by means of a syphonic discharge on to a per- 

 forated distributing disc at intervals of 38 minutes. The sewage dealt with 

 was artificially prepared by diluting liquid cow manure with water, the dilution 

 in the first experiment being 1 in 20 and in the second 1 in 50 to 1 in 100. 

 The suspended solids were removed by rough filtration through glass wool. 



In this case, the filters being new, it was possible to determine the stages 

 in the ripening process, and it was found that while a marked amount of 

 general oxidation was apparent in the effluents from all the filters in two 

 weeks, no trace of oxidised nitrogen appeared until 10 days later, and until 

 then the ammonia in the effluents was the same as in the sewage. The first 

 trace of oxidised nitrogen in the effluents appeared in the form of nitrous 

 nitrogen on the following dates, all three filters having been started on 



February 20th :— 



Deep filter on 18th March. 



Medium „ 21st March. 



Shallow „ 28th March. 



For some time the formation of nitrous nitrogen continued in increasing 

 amount, and later, when nitric nitrogen made its appearance, the nitrous 

 nitrogen gradually diminished until ultimately the effluents from the medium 

 and deep filter showed no trace of it. For some reason it would appear that 

 the effluents from the shallowest filter ceased to be recorded before this period. 



Eegarding the absence of nitrous nitrogen in the effluents after the filters 

 had matured, the results accord with those at Hanley. In one other respect, 

 namely, the reduction of general oxidisable matter, the results also agree 

 with those at Hanley in the fact that practically the reduction was as marked 

 in the shallow as in the deep effluents. 



As regards the degree of nitrification at different depths, Dr. Chick's 

 results do not quite compare with those of Hanley. It must be remem- 

 bered, however, that the conditions differed widely. The volume of sewage 

 dealt with in the former case was relatively greater, and its ammoniacal 

 strength was very much higher. Also the intervals of delivery on to the 

 filter were much longer, namely, 38 minutes compared with 5 minutes in the 

 case of Hanley, and in addition all the disturbing influences incidental to a 

 laboratory experiment of this character have to be taken into account, such 

 as the effect of peripheral capillarity upon the uniformity of the downward 

 flow in a filter of such small diameter. At the same time, the nitrification 

 effected at the medium depth was very considerable, and it would have been 

 interesting to have had another record between that and the 6-ft. 6-in. depth. 



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