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Gas Pressure Modelling


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Hello, I was working to model microbial gas pressure built up as well as the geochemistry in a closed system. I have a few questions below.

  • When I plot the gas partial pressure, I am wondering is that the gas phase partial pressure? Is that calculated by using Henry’s Law in the system? Is there a way to represent the dissolved phase gas?
  • When I plot the pressure under Physical Parameters, it is 1atm. I assume that indicates the pressure condition for the sample and is set by default. Is there any way this pressure could indicate the total pressure build-up in the system?
  • The reaction stuck at step 538, tried to change delxi, but not working, any other parameter I should change? Is it because the major component Nitrate is almost all gone?

Look forward to you reply, thank you!

denitrification_Mary (May 5th, 2021).rea

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Hello Mary,

It represents the gas' partial pressure in equilibrium with the fluid. The partial pressure is calculated using Henry's law. The software itself does not keep track of the gas phase volume. 

Please note that the default database compiles thermodynamic data at 1 atm below 100C or along the steam saturation curve at 100C and above. If you like, you can compile a thermo dataset at the pressure needed for your simulation. You cannot set the confining pressure within React directly. 

 I ran your input file and noticed that your model has rapid biomass growth rate at the end of the simulation, which in combination with nitrate becoming a limiting reactant is causing your simulation to take really small time steps. I would suggest that you check the rate law and its parameter values to make sure they are correct. For example, if you would like to set up an monod type rate law for NO3-, you will need to use the power and powerA pulldown to add NO3-- to the numerator and denominator, respectively, of the Monod term for the electron accepting half-reaction. I suggest you start by keeping the power of 1 and use the molal unit for both options. You might also want to set a half-saturation constant (Ka) for the accepting half-reaction. If you want a Dual-Monod rate law, then you would also do the same thing for acetate, but instead of powerA and Ka, you would want to set up powerD and Kd for the electron donating half-reaction. You can also browse all the available rate law types within the GWB for modeling microbial metabolism in section 4.7.2 of the GWB Essentials User Guide. In the section following (4.7.3) is an example calculation of two competing microbial strains growing by oxidizing acetate. 

Hope this helps,
Jia Wang

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