252 



SEWAGE AND ITS PURIFICATION 



alkaline.^ On the other hand, when the most complete puri- 

 fication and the highest nitrification are occurring, effluents 

 are either acid or only slightly alkaline, and the poorer the 

 nitrification the greater the alkalinity of the liquids.- This 

 follows from the chemical equations. 



At Caterham, with a heavy sewage containing i8 parts of CI 

 per 100,000, Moncrieff began by pushing the preliminary 

 process much further than usual, with the object of ascertain- 

 ing the most favourable point, by estimating the free ammonia, 

 and finding what amount gave the best results in nitric nitrogen. 

 Exceptionally anaerobic conditions were introduced, by means 

 of inverted open-mouthed glazed earthen vessels, about 400 in 



FiG. 25. — Caterham Cultivation Tank. 



number, piled in a tank 20 feet by 10 feet by 9 feet deep, and 

 kept down by weights. Each pot became filled with gases of 

 the character I have described, devoid of ox7gen, so that there 

 were a large number of surfaces on which zooglcea colonies of 

 bacteria could quietly develop in contact with the percolating 

 sewage. The result was an effluent containing 126 parts per 

 100,000 of dissolved soHds, 35 of free NHg, and 5*3 of organic 

 nitrogen, which was now highly toxic to any but anaerobic 

 organisms, and absolutely refused to nitrify. When diluted, 

 however, with a few volumes of natural water it rapidly became 

 purified.^ 



^ Pakes and Jollyman, /. Chem. Soc., April, 1901, p. 459. 



■j Report Mass. State B. of Health, 1905, pp. 227, 229, 238. 



" The Massachussetts Board of Health also observed as to tank and filters at 

 Andover, U.S., that septic action, when carried too far, may make sewage much 

 less amenable to the subsequent action of filters. 



