In bioprocessing it’s usually difficult to calculate things exactly due to the complexity of biological processes. Therefore we tend to make a lot of assumptions.
In your exams or even at work you will need to put all the assumptions you make when doing a mass balance, so I thought I’d write a list of all the common ones that you can use.
Common Assumptions
- No system leakage (best assumption!!)
- Inlet air and outlet gas are dry (liquid does not leave system)
- Cell broth has density of water: 1kg/m3
- Complete conversion of input material (nutrients to product)
- Composition of inlet air is 21% mol O2, 79% N2
- Mass of cells inoculated at start of process is negligible (mainly for batch processes)
- CO2 leaves in outlet gas
- Other media components can be ignored
- O2 and nutrients are available to all cells (vessel broth is homogenous)
There are probably more examples of assumptions you can make, but these are generally applicable to all processes. If you have any questions or want me to add anything, leave a comment and I will get to it ASAP!
Bioprocessing Explained 