## Desorption in MIM model.

A discussion forum for Hydrus-1D users.
vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Desorption in MIM model.

Greetings Dr. Jirka,

I was wondering if one could model the desorption of solute from the column with physical non-equilibrium ?

I have initial soil conc. of solute, all the physical non-equilibrium parameters, and time-conc. data of the leachate.

What parameters will be used to make it a desorption process?

I am a dual porosity model with physical and chemical non equilibrium. I was getting a good fit too. I am Kd (linear sorption) value as calculated after 24 hrs of equilibration of solution in the saturated column. But Kd is used to express sorption and I need to model the desorption of solute.

I would really appreciate your help in this.

Thank you.

Jirka
Posts: 5818
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Desorption in MIM model.

HYDRUS treat both sorption and desorption in the same way and using the same parameters, i.e., the distribution coefficient and the mass transfer coefficient. J.

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Thank you Dr, Jirka. Thats reassuring. I am on the right path then.

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greeting Dr. Jirka,

I am getting a good fit and the optimized parameters also look good. But the mass balance does not make sense. I have a total solute concentration of 177.37 ug/cm3 of soil. I am using a Dual porosity model with physical and chemical non-equilibrium. I know the kd, frac, thlim, alpha, dispersivity. I am optimizing for frac_m and omega.

In the mass balance info. in post-processing, I am getting- ConcVol as 156.27 ug/cm2 while ConcVolIm as 1835.6 ug/cm2. The total is: 1991.87 ug/cm2. The length of the column being 25 cm, will give me the total solute conc. in soil as 1991.87/25= 79.7 ug/cm3. This is far off what had as an input in the GUI.

I am also attaching my model for your convenience. Thank you. I would really appreciate your advice and guidance on this.
Attachments
Mass balance.zip

Jirka
Posts: 5818
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Desorption in MIM model.

You selected that the initial concentration is given in terms of total solute mass and that nonequilibrium phase is initially in equilibrium with the equilibrium phase.

It seems that the old HYDRUS-1D did not properly assigned initial mass to the kinetic sites in the immobile water, since I can see that SorbVolIm2 is initially zero (while ConcVol=30.2 and ConcVolIm=1835; for the first inverse iteration), and only gradually increases (due to kinetic sorption). If I run this with HYDRUS 5, I still get ConcVol=30.2 (mass in mobile zone with instantaneous sorption) and ConcVolIm=1835 (mass in immobile zone), but now SorbVolIm2=1814 (mass on kinetic sites), i.e., this mass is properly assigned.

These are the correct calculations:
ro=1.225
Frac=0.586
Theta=0.538
ThImob=0.211
Kd=276.61
Frac_m=0.01
Mass=177.37

Mass=c*theta+s*ro=c*(theta+Kd*ro)
Conc=Mass/(theta+Kd*ro)=177.37/(0.538+277.6*1.225)=0.521
Sorb2=Frac*(1.-FracM)*kd*conc=0.586*(1-0.01)*276.6*0.521=83.6

ConcVol =Conc*(ThetaM+Frac_m*Frac*Kd*ro) = 0.521*(0.327+0.01*0.586*277.6*1.22)= 1.20
ConcVolIm=Conc*(ThetaIM+(1-Frac)* Kd*ro) = 0.521*(0.211+0.414*277.6*1.22)=73.159
SorbVolIm2 =Sorb2*ro=83.6*1.225=102.41
TotalMass= ConcVol+ ConcVolIm+ SorbVolIm2=1.2+73.159+102.41=177.4= input mass

J.

pS: I attach the project, as well as the exe from HYDRUS 5 (which you should be able to use with HYDRUS-1D).
Attachments
0US5.rar
Hydrus.rar

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Thank you Dr. Jirka for all the help. It really means a lot.
Have a good day sir.

With regards,
Vishawjot Singh Sandhu

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greetings Dr. Jirka,

I am trying to insert the exe. files you attached in the C:\Program Files (x86)\PC-Progress\Hydrus-1D 4.xx folder. This folder already has files with the same name though larger in size. I replace them with new files. But then hydrus doesn't work.

Could you help me out with the issue? I would really appreciate the help.

Thank you sir.

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greetings Dr. Jirka,

I would really appreciate if you could help me out with this one issue. The exe. in the hydrus 1d folder are to be replaced with the ones you attached. But on doing so hydrus does not run any model.

I was hoping if you have an answer to this issue. I appreciate your help so far.

Have a good day.

Thank you.

With Regards,
Vishawjot Singh Sandhu

Jirka
Posts: 5818
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Desorption in MIM model.

Try to run these new computational modules externally (see FAQ on the HYDRUS website on how to do that). If that does not work, you perhaps need to have the following 64bit libraries (https://www.dropbox.com/scl/fo/695s8gzd ... 7v3nb&dl=0). If that does not work either (I was hoping that computational modules from version 5 might work with HYDRUS-1D), you will need to upgrade to version 5 of HYDRUS. J.

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greetings Dr. Jirka,

Thank you for your help and guidance. Installing the above-mentioned libraries worked for me and now I am able to see the sorbVolIm2. The mass balance works out to be fine.

I used the same parameter values and optimized a single parameter as done by you in the OUS5 model. But my curve and value of the optimized parameter vary from yours. I was wondering what may be the reason for that. Even on using the optimized parameter value from your model, I get a different curve.

I really appreciate your help so far. It means a lot.

I am attaching my updated model here.

Thank you. Have a good day sir.

With regards,
Vishawjot Singh Sandhu
Attachments
Updated US6.zip

Jirka
Posts: 5818
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Desorption in MIM model.

I will not have time to look at your project this week, as I’m teaching this week an online HYDRUS short course. J.

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greetings Dr. Jirka,

May you have a good time teaching the online course.

With Regards,
Vishawjot Singh Sandhu

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greetings Dr. Jirka,

I hope you had a great time teaching the Hydrus short course.

with regards,
Vishawjot Singh Sandhu

Jirka
Posts: 5818
Joined: Sat Mar 16, 2002 3:47 pm
Location: USA
Location: Riverside, CA

### Re: Desorption in MIM model.

Yes. I had two courses, one for the US time zone and one for the Asian/Aussie time zone. I believe both were OK (for the attendees). Now, I’m recovering by hiking (during the entire next week) in the Eastern Sierra. Greetings from the Rock Creek Lake. Jirka

vss0015@auburn.edu
Posts: 42
Joined: Thu Nov 10, 2022 8:58 pm
Location: USA

### Re: Desorption in MIM model.

Greetings Dr. Jirka,

Wishing you a good hike and a great week.

Will be waiting for your response next week.

With regards,
Vishawjot Singh Sandhu