236 ELEMENTS OF WATER BACTERIOLOGY 



The following average data for two of the largest 

 trickling filter plants in the United States are cited 

 by Kinnicutt, Winslow and Pratt (1910). 



BACTERIAL CONTENT OF SEWAGE AND EFFLUENTS 

 FROM TRICKLING FILTERS 



It is obvious that effluents of this character cannot be 

 considered satisfactory from the standpoint of bacterial 

 purification. As Houston concluded, after a careful 

 review of the subject, " The different kinds of bacteria 

 and their relative abundance appear to be very much 

 the same in the effluents as in the crude sewage. Thus, 

 as regards undesirable bacteria, the effluents frequently 

 contain nearly as many B. coli, proteus-like germs, 

 spores of B. enteritidis sporogenes and streptococci, 

 as crude sewage. In no case, seemingly, has the reduc- 

 tion of these objectionable bacteria been so marked 

 as to be very material from the point of view of the 

 epidemiologist" (Houston, 1902^. 



Experimental studies with specific bacteria have 

 confirmed these conclusions. Houston (igo4 b ) found 

 that B. pyocyaneus appeared in the effluent of a trickling 

 bed 10 minutes after application to the top and con- 

 tinued to be discharged for 10 days. In septic tanks 

 and contact beds, the same germ persisted for 10 days. 



