Biomass Estimation from OUR Measurement

Biochemical Engineering


Problem Statement: Oxygen utilization rate (OUR) is measured on-line with an oxygen analyzer. Find the equation(s) you might use to estimate biomass concentration from OUR data in a batch bioreactor. Given 1) the following OUR data, 2) that the oxygen-to-biomass yield coefficient is 3 g biomass/g O2, and 3) that the maintenance coefficient is 0.1 g O2/g biomass; calculate the biomass concentration with time.

   Time     OUR          Biomass Conc.
   (h)   (g oxygen/L-h)  (g biomass/L)
   -----------------------------------
    0       0.01             0.1
    1       0.02              ?
    2       0.10              ?
    3       0.20              ?
    :        :                :

Solution:

  OUR(t) = (1/Y)*dx(t)/dt + m*x(t)
     which is rearranged to: dx(t)/dt = Y*(-m*x(t)+OUR(t))
  Euler's approximation of dx/dt: (xi+1-xi)/(ti+1-ti)
  Thus,
  xi+1=xi+Y*(-m*xi+OURi)*(ti+1-ti)

   Time     OUR          Biomass Conc.
   (h)   (g oxygen/L-h)  (g biomass/L)
   -----------------------------------
    0       0.01             0.1
    1       0.02             0.1 +3*(-0.1*0.1 +0.01)*(1-0)=0.1
    2       0.10             0.1 +3*(-0.1*0.1 +0.02)*(2-1)=0.13
    3       0.20             0.13+3*(-0.1*0.13+0.10)*(3-2)=0.39
    :        :                :
This problem is similar to the following file.


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Biochemical Engineering -- Biomass Estimation from OUR Measurement
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