Nitrogen generation in anaerobic digestion

Hello,

i would like to model the ammonia flux in a wastewater treatment plant. I have already set up the model and it works. When it comes to anaerobic digestion there is a formation of ammonia due to nitrogen conversion in the process itself. How can I model such a "generation of mass"?

Thanks in advance!

Due to the law of mass conservation, in material flow analysis mater is generally not allowed to appear or disappear within a process. So the formation of ammonia from nitrogen can only be modelled by adding an additional import flow to your model. Note, that if you also want to model the nitrogen flows (on a nitrogen substance layer) you have to add an additional export flow that is needed to model the "disappearing" (transformed) nitrogen. On the layer of ammonia this "transformed nitrogen" export flow is zero while on the layer of nitrogen the "formed ammonia" import flow is zero.