Food to Microorganism Ratio

Food-to-Microorganism Ratio (F-M)

In general, the Food-to-Microorganism Ratio (F-M) is a measure of the amount of food, or BOD, that is given to the microorganisms in the aeration tank. The microorganisms are the mixed liquor volatile suspended solids, or MLVSS.

Example and calculation

A wastewater treatment has 150000 lbs of mixed liquor volatile suspended solids (MLVSS) in the aeration tank. If the primary effluent has a BOD of 175 mg/L and a flow rate of 35 MGD, then what is the food-to-microorganism (F-M) ratio?

Here,

MLVSS= 150,000 lbs

BOD= 175 mg/L

Flow rate=35 MGD

                              lbs/day of food                               lbs/day of BOD

         F-M ratio =                                                  =                                     

                              lbs of microorganism                      lbs of MLVSS

         mg/L × MGD × 8.34 lbs/gal                175 mg/L × 35 MGD × 8.34 lbs/gal

   =                                                           =                                                                    

          150,000 lbs of MLVSS                    150,000 lbs of MLVSS

51,0825 lbs/day BOD

    =

                      150,000 lbs

          0.34 lb/day BOD

    =

lb MLVSS