156 ILLINOIS STATE ACADEMY OF SCIENCE 



If aerobic conditions prevail, the nitrifying organisms 

 oxidize nitrogen to nitrites and nitrates and the mineral- 

 ization of nitrogen is complete. 



These reactions are pretty well understood and in fact 

 a matter of common knowledge among chemists. The 

 fact that these reactions can take place in the reverse 

 direction has, however, but recently been demonstrated. 



If we start with nitrates we find that under anaerobic 

 conditions they are reduced. This process is generally 

 referred to as denitrification and most authorities state 

 that denitrification results in loss of nitrogen. Experi- 

 ments in our laboratory and elsewhere indicate that this 

 is not true. Nitrates when reduced are sjmthesized into 

 protein, the living protein of micro-organisms and bac- 

 teria. Likewise free ammonia in some cases decreases 

 during the process of sewage treatment, but here again 

 nitrogen is not lost but protein is formed. Thus we see 

 that in sewage treatment we may have protein com- 

 pounds undergoing hydrolysis, liquefaction and oxida- 

 tion, or the reverse action may take place and protein 

 may be precipitated. 



The carbon and sulfur cycles are equally interesting 

 but would be beyond the limits of the time alloted this 

 paper. 



