Oxidation level is depicted as a subjective observable quality from day 
to day observation of:
1.  MLSS increase or decrese
2.  Settleable Solids increase or decrease
3.  Settleable Solids "Floc" quality (See EPA Troubleshooting Guides)
4.  Effluent Quality
5.  General Plant Mixed Liquor Quality
6.  Also, centrifuge testing can relate general sense trends (young to old)
 
*7. MICROSLIDE INSPECTIONS!!!

       Experience will give the operator a good insight into his sludge 
character as to being under or over oxidized (simplisticly young or old).  The 
Microslides will verfiy with a great additional insight as to what is 
happening to cause that sludge character.  (see microslide text)