126 SEWAGE AND ITS PURIFICATION 



that in agriculture it is a retrograde change, involving great loss 

 in the value of manure. But in the treatment of sewage it is 

 capable of rapidly effecting a great amount of purification. Gayon 

 and Dupetit^ isolated two organisms from sewage which, in the 

 presence of organic matter, decomposed nitrates with production 

 of nitrogen and nitrous oxide. In a nitrated medium they were 

 anaerobic, taking oxygen from the nitrate, and in certain solu- 

 tions as much as 9 grammes per litre of nitrate could be decom- 

 posed. It was proved that the nitrate evolves all its N as gas, and 

 that its oxygen combines with the carbon of the organic matter to 

 form CO2, a portion of which may be evolved as gas, while the 

 remainder combines with the base to form an acid carbonate. 

 Organic matter is essential, and " i gramme KNO3 requires 

 0*148 C or o"273 gramme of albuminoid matter for its complete 

 decomposition." The N + N2O + COg account for all the nitrogen 

 and carbon, and for the available oxygen of the nitrate. The 

 denitrifying bacteria will not develop in liquid deprived of 

 nitrate and out of contact with air, nor will they attack organic 

 matter under these circumstances. The authors further proved 

 denitrification to be a fermentation which consists in the direct 

 burning up of organic carbon at the expense of the oxygen of 

 a nitrate.^ Ampolla and Ulpiani^ isolated two of the bacteria 

 which decompose organic matter (such as sugars, fats, and 

 amido-acids) and nitrate to CO2 and N without intermediate 

 production of nitrite ; for example : — 



5C6H12O6+ 24NaN03 = 24NaHC03 + 6CO2 + iSH.O + 12N2. 

 Thus 5 of oxygen are taken from N0O5 instead of 4, as in the 

 production of NgO. This is an even greater utilization of the 

 " available oxygen," and is the reason why an effluent that has 

 been properly fermented and heavily nitrated is capable of rapid 

 self-purification, and also of improving the condition of a river 

 into which it may be discharged. Adeney, in fact, introduced 

 a process in which he added nitrate of soda at the third stage 

 to accomplish by denitrification the final removal of any 

 organic matter present ; but as we have seen that the effluent 



' Station Agronomique de Bordeaux, 1886; " Reduction des Nitrates par les 

 infiniment petits " (Nancy, 1886). 



- My calculation of the "available oxygen " (pp. 16 and 130), is supported by 

 numerous proofs that a large number of bacteria can transfer oxygen as freely 

 from nitrates as from air. Pakes and Jollyman {Jour. CJiem. Soc, March, 1901, 

 p. 324) have actually modified the definition of an anaerobic organism to "one 

 which will not grow in the presence of either free oxygen or of available oxygen 

 in the form of nitrates," and give instances, aerobes being vice versa. 



•^ Gaz. Chim. Ital., xxviii. (i), 410; Jotirn. Soc. Chem. Ind., p. 1160, December, 

 i8q8. 



