270 SEWAGE AND ITS PURIFICATION 



Percentage Purification. 



(i) Oxygen consumed 

 (2) Oxidation of nitrogen 



Average, 



93 

 91*6 



The intermediate stages of the first sample are expressed in 

 the curve (Fig. 30), in which the horizontal figures indicate the 

 trays and the vertical ones the parts of nitrogen. We notice 

 that:— 



Total Oxidized N 

 Nitrous Nitrogen 



12 3 4 5 6 7 



Fig. 30. — Changes of Nitrogen in Oxidizing Trays. 



