272 



SEWAGE AND ITS PURIFICATION 



Sims Woodhead proved that in coke-breeze upward filters at 

 Claybury, in the deeper parts of the filters anaerobic organisms 

 were more numerous, with high ammonia ; while near the sur- 

 face aerobic organisms prevailed and nitrates were predominant. 

 From other experiments he recognised '* that there was a sharp 

 line of distinction between the work done by the anaerobe, and 

 that by the aerobe, and that the two processes should be kept 

 as separate as possible." In these filters, natural working had 

 established separate zones for the two operations, but being too 

 close in one apparatus, they were liable to vary and intrude on 

 one another, and a smell was sometimes present. 



Installations on Scott- Moncrieff's principle have been work- 

 ing in many places in South Africa, where frost does not present 

 any difficulty by retarding the work of the organisms. In cold 

 countries a slight protection seems to be sufficient. At Cater- 

 ham Barracks, England, works were constructed for the War 

 Office, in 1898, to deal on the Moncrieff system with about 

 16,000 gallons daily of an exceptionally strong sewage. 



In 1899, I collected and examined samples representing two 

 cycles of 24 hours, when the filter was producing effluent at an 

 average rate of 340,000 gallons per acre. The average results 

 were : — 



The percentage purification was 



Raw sewage to tank effluent 



,, to finished effluent 



Oxygen 

 Consumed. 



40 



82 



Organic Nitrogen. 



32-5 

 83 



Subsequently on my suggestion two denitrifying tanks were 

 placed after the nitrifying filter. These tanks receive the over- 

 flow from the hydrolytic tank, together with the nitrated 

 effluent, and in this way the oxidizing filters can work to their 



