Degradation of TCE via ZVI

[brflickinger]

Hello,

I am a graduate student trying to model the degradation pathway of TCE using PHREEQC v3.4.0.12927. I am relatively inexperienced with PHREEQC and am looking for any pointers or directions.

Zero valent iron (ZVI) is injected into groundwater aquifers to achieve reductive dechlorination of TCE and its degradation products through the following reactions:

Zvi + 2H2O -> Fe+2 + H2 + 2OH-
TCE + H2 -> cis-1,2-dichloroethene + H+ + Cl-
TCE + H2 -> trans-1,2-dichloroethene + H+ + Cl-
TCE + H2 -> 1,1-dichloroethene + H+ + Cl-
cis-1,2-DCE + H2 ->Vinyl Chloride + H+ + Cl-
trans-1,2-DCE + H2 ->Vinyl Chloride + H+ + Cl-
1,1-dichloroethene + 2H+ -> Ethylene + 2Cl-
Vinyl chloride + H2 -> Ethylene + H+ + Cl-
Ethylene + H2 -> Ethane

We assume that all of these reactions occur simultaneously. It is my goal to be able to plot concentrations of TCE and all of its degradation products over time with various concentrations of ZVI.

I have attached my code so far, but I'm having some issues in my SOLUTION_SPECIES. I'm getting an error that reads "ERROR: Equation does not balance for element" for most of my reactions. What am I doing wrong here? Furthermore, what would be a good strategy to achieve my goals for this project? I have see that some individuals use RATES or KINETICS, but I do not know how to utilize either. Any help is appreciated!

Thanks,
Brandon

Code: [Select]

TITLE Degradation of TCE via ZVI

SOLUTION_MASTER_SPECIES

   Tce         Tce    0.0        C2Cl3H        131.40
   Dceoo       Dceoo    0.0   C2H2Cl2      96.94
   Dcec        Dcec        0.0        C2H2Cl2       96.94
   Dcet    Dcet    0.0   C2H2Cl2      96.94
   Vc          Vc          0.0        C2H3Cl        62.5
   Ethylene    Ethylene    0.0        C2H4          28.5
   Ethane    Ethane    0.0   C2H6      30.07
   Zvi    Zvi    0.0   Fe+0      55.85

SOLUTION_SPECIES
   Tce = Tce;      log_k   0.0
   Dceoo = Dceoo; log_k   0.0
   Dcec = Dcec;      log_k   0.0
   Dcet = Dcet; log_k   0.0
   Vc = Vc;      log_k   0.0
   Ethylene = Ethylene;      log_k   0.0
   Ethane = Ethane; log_k   0.0
   Zvi = Zvi; log_k   0.0
   Zvi + 2H2O = Fe+2 + H2 + 2OH-
log_k   21.95
   Tce + H2 = Dcec + H+ + Cl-
log_k   29.66
   Tce + H2 = Dcet + H+ + Cl-
      log_k   21.98
   Tce + H2 = Dceoo + H+ + Cl-
      log_k   21.39
   Dcec + H2 = Vc + H+ + Cl-
log_k   24.47
   Dcet + H2 = Vc + H+ + Cl-
log_k   21.98
   Dceoo + 2H+ = Ethylene + 2Cl-
log_k   38.56
   Vc + H2 = Ethylene + H+ + Cl-
log_k   26.26
   Ethylene + H2 = Ethane
log_k   17.70

SOLUTION 1 Pure water
   Temp    25
   pH      7.0
   units ug/L
   Tce     50
   Dcet    12
   Dcec    15
   Dceoo   7.0
   Vc      2.0

END


[brflickinger]

Update:

I have changed my SOLUTION_MASTER_SPECIES as shown below, which seemed to have taken care of my original error messages, but I now have new ones, of course!

ERROR: Could not reduce equation to primary master species, C2H6.
ERROR: Could not reduce equation to primary master species, Fe.
ERROR: Could not reduce equation to secondary master species, C2Cl3H.
ERROR: Non-master species in secondary reaction, C2Cl3H.
ERROR: Could not reduce equation to secondary master species, C2H2Cl2.
ERROR: Non-master species in secondary reaction, C2H2Cl2.
ERROR: Could not reduce equation to secondary master species, C2H3Cl.
ERROR: Non-master species in secondary reaction, C2H3Cl.
ERROR: Could not reduce equation to secondary master species, C2H4.
ERROR: Non-master species in secondary reaction, C2H4.
WARNING: Could not find element in database, C2Cl3H.
   Concentration is set to zero.
WARNING: Could not find element in database, C2H2Cl2.
   Concentration is set to zero.
WARNING: Could not find element in database, C2H3Cl.
   Concentration is set to zero.
ERROR: Calculations terminating due to input errors.

Any idea why it cannot find the elements in the database? I have created it in my SOLUTION_MASTER_SPECIES.

Code: [Select]

   Input file: C:\Users\bflic\Desktop\M.S\G202\Project\Reaction2.pqi
  Output file: C:\Users\bflic\Desktop\M.S\G202\Project\Reaction2.pqo
Database file: C:\Program Files (x86)\USGS\Phreeqc Interactive 3.4.0-12927\database\phreeqc.dat

------------------
Reading data base.
------------------

SOLUTION_MASTER_SPECIES
SOLUTION_SPECIES
PHASES
EXCHANGE_MASTER_SPECIES
EXCHANGE_SPECIES
SURFACE_MASTER_SPECIES
SURFACE_SPECIES
RATES
END
------------------------------------
Reading input data for simulation 1.
------------------------------------

DATABASE C:\Program Files (x86)\USGS\Phreeqc Interactive 3.4.0-12927\database\phreeqc.dat
TITLE Degradation of TCE via ZVI
SOLUTION_MASTER_SPECIES
   C(0)        C2Cl3H    0.0        C2Cl3H        131.40
   C(0)        C2H2Cl2    0.0   C2H2Cl2      96.94
   C(0)        C2H2Cl2     0.0        C2H2Cl2       96.94
   C(0)    C2H2Cl2    0.0   C2H2Cl2      96.94
   C(0)       C2H3Cl      0.0        C2H3Cl        62.5
   C(0)       C2H4        0.0        C2H4          28.5
   C(0)       C2H6    0.0   C2H6      30.07
   Fe(0)    Fe+0    0.0   Fe+0      55.85
   H    H+   -1.0        H+     1.008
   H(0)    H2    0.0   H2     1.008
   Cl     Cl-    0.0   Cl-     35.453
SOLUTION_SPECIES
   C2Cl3H = C2Cl3H
      log_k   0.0
   C2H2Cl2 = C2H2Cl2
log_k   0.0
   C2H2Cl2 = C2H2Cl2
      log_k   0.0
   C2H2Cl2 = C2H2Cl2
log_k   0.0
   C2H3Cl = C2H3Cl
      log_k   0.0
   C2H4 = C2H4
      log_k   0.0
   C2H6 = C2H6
log_k   0.0
   Fe+0 = Fe+0
log_k   0.0
   Fe+0 + 2H2O = Fe+2 + H2 + 2OH-
   log_k   21.95
   C2Cl3H + H2 = C2H2Cl2 + H+ + Cl-
   log_k   29.66
   C2Cl3H + H2 = C2H2Cl2 + H+ + Cl-
   log_k   21.98
   C2Cl3H + H2 = C2H2Cl2 + H+ + Cl-
   log_k   21.39
   C2H2Cl2 + H2 = C2H3Cl + H+ + Cl-
   log_k   24.47
   C2H2Cl2 + H2 = C2H3Cl + H+ + Cl-
   log_k   21.98
   C2H2Cl2 + 2H+ = C2H4 + 2Cl-
   log_k   38.56
   C2H3Cl + H2 = C2H4 + H+ + Cl-
   log_k   26.26
   C2H4 + H2 = C2H6
   log_k   17.70
SOLUTION 1 Pure water
   Temp    25
   pH      7.0
   units ug/L
   C2Cl3H     50
   C2H2Cl2    12
   C2H2Cl2    15
   C2H2Cl2   7.0
   C2H3Cl      2.0
END
-----
TITLE
-----

 Degradation of TCE via ZVI

ERROR: Could not reduce equation to primary master species, C2H6.
ERROR: Could not reduce equation to primary master species, Fe.
ERROR: Could not reduce equation to secondary master species, C2Cl3H.
ERROR: Non-master species in secondary reaction, C2Cl3H.
ERROR: Could not reduce equation to secondary master species, C2H2Cl2.
ERROR: Non-master species in secondary reaction, C2H2Cl2.
ERROR: Could not reduce equation to secondary master species, C2H3Cl.
ERROR: Non-master species in secondary reaction, C2H3Cl.
ERROR: Could not reduce equation to secondary master species, C2H4.
ERROR: Non-master species in secondary reaction, C2H4.
WARNING: Could not find element in database, C2Cl3H.
Concentration is set to zero.
WARNING: Could not find element in database, C2H2Cl2.
Concentration is set to zero.
WARNING: Could not find element in database, C2H3Cl.
Concentration is set to zero.
ERROR: Calculations terminating due to input errors.
-------------------------------
End of Run after 0.059 Seconds.
-------------------------------

[dlparkhurst]

You will not be able to define your species as composed of C and Cl. Even if you find balanced equations and equilibrium constants for all of the TCE species, any reaction calculation will instantaneously decompose them all to CO2 species, CH4, and Cl-, and there will be negligible amounts of TCE species.

You are on the right track when defining each of the TCE species as a separate element (SOLUTION_MASTER_SPECIES) and one aqueous species (SOLUTION_SPECIES). It will then be necessary to define kinetic reactions (KINETICS and RATES) that convert one species (element) to the next.

The formula for KINETICS to convert trichloroethylene to dichloroethane, for example, would be
-formula Tce -1 H -3 Dce +1 Cl +1 

Attached is an example of sequential kinetic reactions from PHAST example 2.

[brflickinger]

Thank you for the quick reply Dr. Parkhurst. Does this mean I need to rename my species back to the way I originally had them as such as:

Code: [Select]

SOLUTION_MASTER_SPECIES

   Tce         Tce    0.0        C2Cl3H        131.40
   Dceoo       Dceoo    0.0   C2H2Cl2      96.94
   Dcec        Dcec        0.0        C2H2Cl2       96.94
   Dcet    Dcet    0.0   C2H2Cl2      96.94
Or do I need to remove the formula gfw as well?

[dlparkhurst]

No doctorate, so no Dr.

Yes, use the original definitions (Tce, Dceoo, ...).

I forgot, but the formula may need to include Fe, depending on how you set up the reactions. If you treat Zvi as a dissolved species, then the formula for each KINETIC reaction should include the appropriate stoichiometry for loss of Zvi and gain of Fe in solution. Note that kinetics formulas do not consider charge of an element, only the net transfer of an element into, or out of solution.

If you set the solution in equilibrium with iron metal (say Fe in llnl.dat), then you would not use Zvi as an element, and you would not add Fe in the kinetic reaction. Fe metal would react as necessary to maintain equilibrium as the result of the kinetic reactions.

[Pak]

Doctor in my heart, they should give you an honoris causa.

[brflickinger]

Well, I've definitely made some progress and learned a great deal, but I return with more questions.

1) In the example you provided in the RATES block, I see that:

10 rate = -TOT("Tce") * 0.05/(3600*24)

I understand that this is taking the total amount of TCE, and converting the time to days, however I am unsure what the 0.05 represents. Judging by how the following species have this number halved, I assume it represents a weight as to how "fast" the reaction will proceed, or because it occurs first, it will be the primary degradation rate and thus this number is higher. Is that correct?

Also, I have attached my script as it exists currently - I resolved the issues with the SOLUTION_MASTER_SPECIES and the script was running error free, until I began adding RATES and KINETICS, of course. Please see below for my output and errors:

Code: [Select]

   
   Input file: C:\Users\bflic\Desktop\M.S\G202\Project\Reaction20190422.pqi
  Output file: C:\Users\bflic\Desktop\M.S\G202\Project\Reaction20190422.pqo
Database file: C:\Program Files (x86)\USGS\Phreeqc Interactive 3.4.0-12927\database\phreeqc.dat

------------------
Reading data base.
------------------

SOLUTION_MASTER_SPECIES
SOLUTION_SPECIES
PHASES
EXCHANGE_MASTER_SPECIES
EXCHANGE_SPECIES
SURFACE_MASTER_SPECIES
SURFACE_SPECIES
RATES
END
------------------------------------
Reading input data for simulation 1.
------------------------------------

DATABASE C:\Program Files (x86)\USGS\Phreeqc Interactive 3.4.0-12927\database\phreeqc.dat
TITLE Degradation of TCE via ZVI
SOLUTION_MASTER_SPECIES
   Tce         Tce    0.0        C2HCl3        131.40
   Dceoo       Dceoo    0.0   C2H2Cl2      96.94
   Dcec        Dcec        0.0        C2H2Cl2       96.94
   Dcet    Dcet    0.0   C2H2Cl2      96.94
   Vc          Vc          0.0        C2H3Cl        62.5
   Ethylene    Ethylene    0.0        C2H4          28.5
   Ethane    Ethane    0.0   C2H6      30.07
   Zvi    Zvi    0.0   Fe+0      55.85
SOLUTION_SPECIES
   Tce = Tce
      log_k   0.0
   Dceoo = Dceoo
log_k   0.0
   Dcec = Dcec
      log_k   0.0
   Dcet = Dcet
log_k   0.0
   Vc = Vc
      log_k   0.0
   Ethylene = Ethylene
      log_k   0.0
   Ethane = Ethane
log_k   0.0
   Zvi = Zvi
log_k   0.0
PHASES
ZVI
   Zvi + 2H2O = Fe+2 + H2 + 2OH-
   log_k   21.95
   no_check
Cis
   Tce + H2 = Dcec + H+ + Cl-
   log_k   29.66
   no_check
Trans
   Tce + H2 = Dcet + H+ + Cl-
   log_k   21.98
   no_check
Oneone
   Tce + H2 = Dceoo + H+ + Cl-
   log_k   21.39
   no_check
CisVC
   Dcec + H2 = Vc + H+ + Cl-
   log_k   24.47
   no_check
TransVC   
   Dcet + H2 = Vc + H+ + Cl-
   log_k   21.98
   no_check
Oneoneeth   
   Dceoo + 2H+ = Ethylene + 2Cl-
   log_k   38.56
   no_check
VCeth 
   Vc + H2 = Ethylene + H+ + Cl-
   log_k   26.26
   no_check
Ethyletha
   Ethylene + H2 = Ethane
   log_k   17.70
   no_check
SOLUTION 1 Pure water
   Temp    25
   pH      7.0
   units ug/L
   Tce     50
RATES
        Tce_decay
        start
10 rate = -TOT("Tce") * .05/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
        end
        Dcec_decay
        start
10 rate = -TOT("Dcec") * .02/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
        end
        Dcet_decay
        start
10 rate = -TOT("Dcet") * .02/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
        end
        Dceoo_decay
        start
10 rate = -TOT("Dceoo") * .02/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
        end
  Vc_decay
        start
10 rate = -TOT("Vc") * .01/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
  end
  Ethylene_decay
        start
10 rate = -TOT("Ethylene") * .005/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
  end
  Ethane_decay
        start
10 rate = -TOT("Ethane") * .0025/(3600*24)
20 moles = rate * TIME * SOLN_VOL
30 SAVE moles
  end
KINETICS 1
        Tce_decay
                formula Tce -1 H -3 Dcec +1 Cl- +1
                m 0
        Tce_decay
                formula Tce -1 H -3 Dcet +1 Cl- +1
                m 0
        Tce_decay
                formula Tce -1 H -3 Dceoo +1 Cl- +1
                m 0
        Dcec_decay
                formula Dcec -1 H -3 Vc +1 Cl- +1
                m 0
        Dcet_decay
                formula Dcet -1 H -3 Vc +1 Cl- +1
                m 0
        Dceoo_decay
                formula Dceoo -1 H -2 Ethylene +1 Cl- +2
                m 0
  Vc_decay
                formula Vc -1 H -3 Ethylene +1 Cl- +1
                m 0
  Ethylene_decay
                formula Ethylene -1 H+ -2 Ethane +1
                m 0
END
-----
TITLE
-----

 Degradation of TCE via ZVI

-------------------------------------------
Beginning of initial solution calculations.
-------------------------------------------

Initial solution 1. Pure water

-----------------------------Solution composition------------------------------

Elements           Molality       Moles

Tce               3.805e-07   3.805e-07

----------------------------Description of solution----------------------------

                                       pH  =   7.000   
                                       pe  =   4.000   
      Specific Conductance (µS/cm,  25°C)  = 0
                          Density (g/cm³)  =   0.99704
                               Volume (L)  =   1.00297
                        Activity of water  =   1.000
                 Ionic strength (mol/kgw)  =   1.006e-07
                       Mass of water (kg)  =   1.000e+00
                 Total alkalinity (eq/kg)  =   1.216e-09
                    Total carbon (mol/kg)  =   0.000e+00
                       Total CO2 (mol/kg)  =   0.000e+00
                         Temperature (°C)  =  25.00
                  Electrical balance (eq)  =  -1.216e-09
 Percent error, 100*(Cat-|An|)/(Cat+|An|)  =  -0.60
                               Iterations  =   2
                                  Total H  = 1.110124e+02
                                  Total O  = 5.550622e+01

----------------------------Distribution of species----------------------------

                                               Log       Log       Log    mole V
   Species          Molality    Activity  Molality  Activity     Gamma   cm³/mol

   OH-             1.013e-07   1.012e-07    -6.995    -6.995    -0.000     -4.14
   H+              1.000e-07   1.000e-07    -7.000    -7.000    -0.000      0.00
   H2O             5.551e+01   1.000e+00     1.744    -0.000     0.000     18.07
H(0)          1.416e-25
   H2              7.079e-26   7.079e-26   -25.150   -25.150     0.000     28.61
O(0)          0.000e+00
   O2              0.000e+00   0.000e+00   -42.080   -42.080     0.000     30.40
Tce           3.805e-07
   Tce             3.805e-07   3.805e-07    -6.420    -6.420     0.000     (0) 

------------------------------Saturation indices-------------------------------

  Phase               SI** log IAP   log K(298 K,   1 atm)

  H2(g)           -22.05    -25.15   -3.10  H2
  H2O(g)           -1.50     -0.00    1.50  H2O
  O2(g)           -39.19    -42.08   -2.89  O2

**For a gas, SI = log10(fugacity). Fugacity = pressure * phi / 1 atm.
  For ideal gases, phi = 1.

-----------------------------------------
Beginning of batch-reaction calculations.
-----------------------------------------

Reaction step 1.

WARNING: Negative moles in solution for Cl, -1.325269e-13. Recovering...
WARNING: Negative moles in solution for Cl, -9.276882e-15. Recovering...
WARNING: Negative moles in solution for Cl, -6.493817e-16. Recovering...
WARNING: Negative moles in solution for Cl, -4.545672e-17. Recovering...
WARNING: Negative moles in solution for Cl, -3.181970e-18. Recovering...
WARNING: Negative moles in solution for Cl, -2.227379e-19. Recovering...
WARNING: Negative moles in solution for Cl, -1.559165e-20. Recovering...
WARNING: Negative moles in solution for Cl, -1.091416e-21. Recovering...
WARNING: Negative moles in solution for Cl, -7.639911e-23. Recovering...
WARNING: Negative moles in solution for Cl, -5.347938e-24. Recovering...
WARNING: Negative moles in solution for Cl, -3.743556e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.310245e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.467474e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.643571e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.104480e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.237017e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.385459e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.551714e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.737920e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.946471e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.090024e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.017355e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.139438e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.276170e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.429311e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.600828e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.075757e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.204847e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.349429e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.511361e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.692724e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.895851e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.061676e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.189078e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.109806e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.242982e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.392140e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.559197e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.047780e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.173514e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.314336e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.472056e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.648703e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.846547e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.034066e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.158154e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.080944e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.210657e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.355936e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.518649e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.020532e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.142996e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.280155e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.433774e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.605827e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.798526e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.007174e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.128035e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.052833e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.179173e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.320674e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.479155e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.656653e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.113271e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.246863e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.396487e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.564066e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.751753e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.961964e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.098700e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.025453e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.148507e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.286328e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.440688e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.613570e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.084319e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.214438e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.360170e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.523390e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.706197e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.910941e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.070127e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.198542e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.118639e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.252876e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.403221e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.571608e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.056120e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.182855e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.324797e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.483773e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.661826e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.861245e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.042297e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.167373e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.089548e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.220294e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.366729e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.530737e-25. Recovering...
WARNING: Negative moles in solution for Cl, -1.028655e-25. Recovering...
ERROR: Execution canceled by user.
--------------------------------
End of Run after 19.434 Seconds.
--------------------------------



So PHREEQC seems to be all good with my code up until running the actual simulation. Why would it be producing negative moles? The KINETICS block should just be producing Cl-. I suspect it is because of the "-" in block 10 of the RATES block?

Thanks,

Brandon

[dlparkhurst]

The main issue is with the sign convention. It can be confusing. The transfer of an element is based on the product of the saved "moles" and the stoichiometric coefficient in the -formula.

If the product is positive, the concentration of the element increases in solution. If negative, the concentration of the element decreases.

However, the other issue is what happens to moles of kinetic reactant: -M in KINETICS. If moles SAVE'd is positive, then M decreases. If moles is negative, M increases. But, if M is zero and moles saved is positive, no reaction occurs (no reactant is available to react).

You had negative moles and negative coefficient for Tce, therefore the reaction is to increase the concentration of Tce in solution, the opposite of what you want. You have two choices.

(1) I switched the moles to be positive, just because it was easier than changing all the formula coefficients. However, M will decrease and it was specified as zero for all reactants in KINETICS. No reaction would occur, so I simply increased the initial amounts of reactants to 10. The amount of kinetic reactants will decrease from 10 as time proceeds. Because M is not used in the RATES definition, it will make no difference.

(2) You could keep the moles SAVE'd as negative and reverse all of the coefficients. If you do that, you can maintain zero for the initial M, and amounts of reactant will increase from zero as time proceeds.

[brflickinger]

This was extremely helpful. I have been working on changing this to apply more for my needs, but one more follow-on question regarding the formula coefficients that you have in your attachment.

Take for example, the reaction of cis-1,2-DCE and H2 to produce vinyl chloride, a hydrogen atom, and a chlorine atom. In the attachment you provided, the formula line for this kinetic step reads:

    -formula  Cl-  1 Dcec  -1 H  -3 Vc  1

Based on the chemical reaction, I would think that this should read something like:

    -formula Cl-  1 Dcec  -1 H2 -1 H+ 1 Vc 1

Is there a reason that you put a -3 coefficient on just the H in your version?

[dlparkhurst]

My bad. Yours will work, although again, the charge on the elements is not used.

Net is

DCE -1 H -1 Vc 1 Cl 1

[brflickinger]

Excellent. Thanks again for your help on all of this Mr. Parkhurst. I'll post my script for reference once I have completed it.

[Vidhi]

Hello,

I am modeling the same. I would like to know how you calculated the log K value for all the compoundsH

[Vidhi]

If I have to introduce a spike of TCE at the 15th day, how can I write the codes for that?

[dlparkhurst]

If you are using TRANSPORT, then you would run the transport simulation for 15 days, then define a new SOLUTION 0 containing TCE, and then define a new TRANSPORT simulation for the period that TCE is introduced.

Alternatively, you could run TRANSPORT, then use REACTION to add TCE to cell 1 (...END; USE solution 1; REACTION ...; SAVE solution 1; END), then run another TRANSPORT simulation.

[Vidhi]

Thank you so much. It was very helpful.
I am working on another model now which is a batch system.  I have introduced groundwater parameters , TCE, cDCE and tDCE, along with propionate and ZVI. The ZVI product used here is anti methanogenic.

In the model, there is dechlorination, some methane formation, high pH and heavy precipitation of minerals. Now I fixed the pH to 6.5, which is ideal for fermentation. At this pH, dechlorination is the same as before, but methane formation spikes, and carbonate concentration is much higher and precipitation much lower. Since the ZVI product is anti methanogenic, how can I write codes to curb the methane formation?

Thank you so much for the help.

[dlparkhurst]

If you just want to disable methane formation, you can simply decrease the log K of the methane reaction.

Code: [Select]

SOLUTION_SPECIES
CO3-2 + 10 H+ + 8 e- = CH4 + 3 H2O
#-log_k 41.071
       -log_k   0
END
[code]

I leave it to you whether your overall reaction sequence is thermodynamically reasonable.