BACTERIAL PURIFICATION 



241 



The high free ammonia and the low albuminoid show that 

 the sewage has already undergone the preparation I have men- 

 tioned. The nitrification of the effluent has not proceeded as 

 far as might have been expected, notwithstanding the very 

 large loss of ammonia, but better results have since been 

 obtained.^ The oxidation of the carbonaceous matter is also 

 marked. Houston's bacteriological examination of this filter 

 has already been referred to (p. 87). 



eh4t^^'tuUiJUiin* 



^y**WimXAX«JC^ 



Fig. 23. — Section of Ducat's Filter. 





' >4 -U K ^« 



Fig. 24. — Filtering Material. 



Figs. 23 and 24 are from Mr. Mansergh's Baltimore Report, 

 1899. 



A great difficulty attending the processes aiming at the direct 

 oxidation, of sewage by currents of air is the cooling produced, 

 which in winter may actually occasion freezing. To avoid this 

 several inventors have introduced systems of artificial warming, 

 with an additional view of stimulating the bacteria, but also 

 with a considerable added expense. Colonel Ducat, as we have 

 seen, provided a series of hot-water pipes for heating in winter. 

 The effect of cold in diminishing the activity of nitrifying 



1 Royal Co77tmission, vol. ii., 1902, pp. 138, 145. 



16 



