250 SEWAGE AND ITS PURIFICATION 



That is to say, the anaerobic bacteria have acted in the usual 

 way : (i) They have dissolved 16 parts per 100,000 of the solid 

 matters or sludge, thereby increasing the solids in solution from 

 64 to 80; (2) Some of the ammonia has been changed into, 

 almost certainly, nitrite ; (3) i*i6 parts of carbon (25 per cent.) 

 and I'l parts of nitrogen (44 per cent.) have been eliminated 

 as non-ammoniacal gases, methane, N, and nitrogen oxides, 

 v^^ith probably some CO2. 



Mr. Moncrieff constructed at Ashtead in 1891 a bacterial 

 tank into which the crude sewage was admitted from below and 

 gradually passed upwards over the surface of a bed of stones. 

 The liquefaction of the solids was so effective that the whole 

 sludge of seven years from a household of ten persons was 

 absorbed on g square yards of land. The space beneath the 

 under-grating of the tank had a capacity of less than 5 cubic 

 feet, and would obviously have filled up in a short time but for 

 the liquefying action that had taken place (Fig. 30, p. 268). 



In 1892 his process was examined by Dr. Houston and later 

 by Dr. Sims Woodhead and myself. We showed that the 

 effluent retains the ammonia produced by the hydrolysis, 

 together with residues of nitrogenous and carbonaceous dis- 

 solved matters, so that judged by ordinary standards of analysis, 

 this liquid contained, as Groves pointed out, a large amount of 

 easily -decomposable nitrogenous organic matter in solution. This 

 great instability of the organic compounds that come over from 

 cultivation tanks is the principal feature of the process. 



There was still a belief that hydrolysis and aerobic nitrifica- 

 tion could be carried on successfully in the same tank, and at 

 Aylesbury air was forced in by a steam jet with this object in 

 view, but the result was unsatisfactory. It became evident 

 that the nitrogenous organic matter must be as far as possible 

 broken up into ammonia before being oxidized to nitrates, and 

 that these two reactions should be carried on in separate areas, 



