The working volume of the reactor is 50 m3. The gas flow rate into the reactor is 0.75 vvm (volume gas per volume liquid per minute). Using the instrumentation available to you, you can confirm an inlet and outlet O2 concentration in the gas phase of 40% and 16% by volume, respectively. For the purposes of your calculation, you reasonably assume the flow rate across the reactor is constant. You find that the residual dissolved oxygen concentration in your system is 2.5 mg L-1 and confirm that the saturation dissolved oxygen concentration achieved on sparging water with air at 30oC is 7.5 mg L-1.
1. Knowing that temperature influences the rate of gas-liquid mass transfer, you decide to calculate the saturation dissolved oxygen concentration at 30oC using the enriched gas stream containing 40% oxygen.
2. Using a mass balance across the reactor, you further calculate the Oxygen Utilisation Rate (OUR)
volume of the reactor = 50m³
gas flow rate = 0.75 vvm
gas flow rate into the reactor = 0.75 × 50 = 37.5m³/min = 0.625m³/sec
inlet concentration of O2 = 40%
outlet concentration of O2 = 16%
percentage used = 24%