192 



Elements of Water Bacteriology. 



McGowan, Houston, and Kershaw (1904) report the 

 following figures for English sewage farms. 



ANALYSIS OF EFFLUENTS FROM SEWAGE FARMS. 

 (McGOWAN, HOUSTON, AND KERSHAW, 1904.) 



The newer bacterial processes, contact beds, and trick- 

 ling filters naturally show a much less satisfactory 

 bacterial removal than sand filtration beds. In the 

 Columbus experiments, Johnson (1905) found from one 

 to two million bacteria in the effluents of contact beds 

 and from 750,000 to 1,900,000 in the effluents from 

 trickling filters. The average percentage reduction effected 

 by seven contact beds and six trickling filters is shown 

 below. 



