Dear David, Thank you for your prompt reply! You have solved my problem, but the question still remains: How does PHREEQC recognize a reductant in the CH2O (this compound had not been defined in database)? Does PHREEQC check a valency of each element? I did not find any explanation to this in the Manual. Sincerely, MIchael -----Original Message----- From: David L Parkhurst [SMTP:dlpark@xxxxxxxx] Sent: á 13 àåâåñè 2001 18:05 To: Michael Zilberbrand Subject: Re: De-nitrification questions : TITLE Denitrification to N2 SELECTED_OUTPUT * reset false * file Denitrif_res.prn * reaction true * si calcite * pH * molalities NO3- K+ EQUILIBRIUM_PHASES 1 Calcite 0.0 SOLUTION 1 Temp 15.0 pH 7.0 N(5) 3.0 K 3.0 N(0) 0.0 REACTION 1 CH2O 1.0 3.75 mmol END This definition is fine. The CH2O gets added to solution and will use the thermodynamically preferred electron acceptor. In this case nitrate will be used because it is the on ly electron acceptor that is available. If the amount of CH2O is sufficient, the reaction will start to make ammonium and eventually it will generate methane. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Dear David, I have a question concerning the 7th example in the PHREEQC manual. There, CH2O(NH3)0.07 is added using REACTION block. How does the program know a way of treating this compound (to what components to destroy it)? Is it defined by setting nil concentrations of CO2, CH4, N2 and NH3 in the GAS_PHASE block? Can I use this way in modeling the pH change in de-nitrification reaction CH2O + 0.8NO3- + 0.8H+ = 1.4H2O + 0.4N2 + CO2 without using the GAS_PHASE block? Is the following input file true? TITLE Denitrification to N2 SELECTED_OUTPUT -reset false -file Denitrif_res.prn -reaction true -si calcite -pH -molalities NO3- K+ EQUILIBRIUM_PHASES 1 Calcite 0.0 SOLUTION 1 Temp 15.0 pH 7.0 N(5) 3.0 K 3.0 N(0) 0.0 REACTION 1 CH2O 1.0 3.75 mmol END In this case it did not matter whether I set or didn't set N(0) in SOLUTION 1. I feel that I don't understand here something! Shouldn't I define somewhere a reaction of CH2O oxidation? Where this should be done? Could you please help me? Sincerely, Michael Zilberbrand
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