Fig. 41. (A) Aeration tanks in activated sludge system. Air is 

 pumped rapidly into the sewage that has been inoculated with activated 

 sludge, and rapid oxidation of organic matter takes place. (B) An empty 

 aeration tank. Many small bubbles are formed by forcing air through 

 the long porous plates visible at the left on the bottom of the tank. 

 {From Microbiology, W. B. Sarles, W. C. Frazier, J. B. Wilson, and S. D. 

 Knight. Copyright 1951, Harper and Brothers, New York.) 



246 



