THE ACTION OF CERTAIN BACTERIA ON SEWAGE 149 



The chtmical results in those experiments in which four 

 cf the bacteria were inoculated into one flask were very ir- 

 regular and disappointing. The time of incubation was ap- 

 parently insufficient for any one or any combination of the 

 bacteria to establish themselves chemically. 



In the experiments in which all of the bacteria were in- 

 oculated into one flask there w T as but one change worthy of 

 note. That was the increase in the nitrates in all of the ex- 

 periments. This was found under both aerobic and anaerobic 

 conditions, amounting in one instance to six parts per mil- 

 lion. There was a decided decrease in the rest of the nitrogen 

 present. 



SUMMARY AND CONCLUSIONS 



Certain bacteria have been studied to determine their effect 

 upon sewage. Those selected were B. coli, R. cloacae, B. pyo- 

 cyaneus, B. vulgar ix, B. mesewtericus var. rnber, and B. sub- 

 tilis. They were selected because they represent aerobic types 

 which are found frequently or constantly in sewage. The 

 effects of these bacteria were studied in fresh sewage, filtered 

 and sterilized by heat at 120 C. (15 pounds pressure) for 

 forty-five minutes. They were studied under aerobic and 

 anaerobic conditions, also in pure and in mixed cultures. 

 Particular attention was paid to the changes in free ammonia, 

 organic nitrogen, nitrites and nitrates. 



Bacteriological ly it was shown that B. coli was completely 

 overgrown under anaerobic conditions in the twenty-four hour 

 period. Under aerobic conditions it was able to overgrow B. 

 pyocyancus, but was overgrown by the rest of the bacteria 

 studied. 



When grown in pure cultures, with the exception of B. 

 proteus, the bacteria gave more constant results under aerobic 

 than anaerobic conditions. 



B. subtilis showed a marked ammonifying power through- 

 out the work under aerobic conditions. Under anaerobic con- 

 ditions it regularly decreased the free ammonia and organic 

 nitrogen content, increasing the nitrites and nitrates, especi- 

 ally the latter. 



