154 ILLINOIS STATE ACADEMY OF SCIENCE 



spiral. If we continue to go round and round this spiral 

 we eventually arrive in nature at a condition where a 

 fairly considerable portion of the organic matter has 

 been mineralized and a black stable humus substance 

 remains. 



Sewage treatment by means of biolytic tanks, sprink- 

 ling, or contact filters and subsequent secondary tanks 

 gives us practically the result indicated by the spiral. 

 The heavy solids are attacked and worked over by cer- 

 tain groups of bacteria in the sludge digestion chamber 

 of the biolytic tank until practically nothing but a black 

 humus remains. The liquefied product, together with 

 the collodial and dissolved organic matter in the sewage, 

 is taken in by the organisms of the biological jelly on the 

 sewage filter. In this jelly the same spiral of activities 

 goes on. A cross-section cut with a knife through the 

 growth on the sewage filter stone shows on the outside 

 the new whitish growth composed of various types of 

 bacteria and protozoa. Just below this new growth there 

 is a layer of less active dying or dead bacterial filaments 

 upon which varieties of protozoa are feeding. These 

 protozoa in turn die, and various forms follow, undoubt- 

 edly, including some of the same anaerobic forms which 

 are active in the sludge digestion chamber of the tanks, 

 which produce immediately adjacent to the stone a black 

 stable humus. From time to time this humus sloughs 

 off and is finally worked over in the digestion chamber 

 of the secondary tanks. As a result of allowing this 

 process to go on to the limit we obtain a relatively small 

 amount of comparatively inoffensive sludge of low N 2 

 content, the N 2 having been largely converted into am- 

 monium salts. The process, however, requires rather a 

 large area for its practical application. 



In the Activated Sludge Process, we start out with the 

 idea that the sludge is a valuable fertilizing material, 

 and therefore for the most economical operation of the 

 process Ave should try to get as much sludge as possible. 

 Since it is a biological process the course of the reaction 

 will be along the course of the same spiral described 

 above. But since we are going to considerable expense 

 in order to provide a condition favorable for the growth 



