In the present paper, the biology of aerobic stabilization of proteinaceous wastes from starch extraction and manioc meal manufacture from "mandioca brava" roots is studied. "Mandioca brava" (Manihot esculenta) is a native plant of great economic importance in Brazil. Wastes from this manufacture have high concentration of organic matter and cyanide and so they are improper to be discharged into rivers without previous stabilization. This stabilization has been achieved successfully through oxidation ditches treatment. The main purposes to be attained with these biological studies were: 1. to know the biological composition and the microstructure of the floes obtained by aeration; 2. to determine the causes and eventually the process of correcting the bulking which often appears in these systems; 3. to know the sequence of microbiologic populations which appear during the stabilization process in order to make possible the use of microscopy to control effectiveness of the treatment. Aeration of the waste was done in the laboratory and results of the microscopic examination were compared with the data as: pH, odor, amount of sludge and relative stability as indicators of the stabilization process evolution. The following conclusions are attained: 1. The floes are formed of a biological mass where filamentous fungi and yeast cells predominate (<a href="/img/revistas/rsp/v1n2/02f2.gif">Fig. 2</a>) ; 2. These floes are loose and so, responsible for the bulking: 3. Addition of phosphorus to the system produces complete biological modification and changes the microstructure of the floes. It produces more favorable conditions to bacteria growth and a heavier floe results (<a href="/img/revistas/rsp/v1n2/02f1.gif">Fig. 1</a>, <a href="/img/revistas/rsp/v1n2/02f2.gif">Fig. 2c</a>) ; 4. The sequence of microscopic organisms as well as their ecological relation with different steps of the process are stablished. So it was possible to recognise those steps by microscopic examination and to control the effectiveness of stabilization (<a href="/img/revistas/rsp/v1n2/02f3.gif">Fig. 3</a>).
