BOD is Biochemical Oxygen Demand and is the amount of Dissolved Oxygen (DO) consumed by microorganisms for the biochemical oxidation of organic and inorganic matter. This is a five day test that's why it's a lot of times shown as BOD5. Much has been written about BOD and by going to any wastewater treatment site on the WEB, you can find information about BOD. The BOD test was developed to predict the effect of wastewater on receiving streams and to determine their capacity to assimilate the organic matter.

The mass transfer of oxygen in water is a complex issue and a number of researchers have made lifetime studies of this one theme. Reference to oxygen transfer by bubbles could be right in some instances mainly in a fermenter where protein covers the bubble surface. That's why in fermenters they use impellers and air injectors. There are formulas like 20 CFM of air per 1,000 cubic feet of water will create a DO of 1+ mg/L. We have found if you use an air injector such as a Mazzei you will have excellent mass transfer at low horsepower.