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Modeling DBP Formation in WaterCAD V8i

evstangelo
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Hello,

I have just started modeling with constituents. My question is what would be the best approach to modeling DBPs (i.e. THMs) in WaterCAD v8i SelectSeries 3? In the field, this would be a combination of chlorine levels, water age, seasonal temps (summer) etc... Would the best way be to find where in the model you have a combination of the high chlorine levels + high water age, and then create a constituent with a positive bulk reaction rate to represent growth and then to be dispersed from nodes in those areas? I am just having a hard time converting this to "model form" as I like to call it. Not sure how to factor temperature into this either, as high temps cause more problems. Any feedback would be greatly appreciated.

Thank you!!

  • 0 Offline
    There are two general ways to model this with WaterGEMS.

    The simpler way is to model DBP formation as a constituent that grows to reach an equilibrium concentration. You would start with a calibrated EPS model and then define a bulk and wall reaction rate and equilibrium concentration. You can try to get a handle on the bulk and equilibrium values with some bottle tests in the lab. If you want to have confidence in the model, you will eventually need to do some field calibration work until you can reasonably match the field measurements. You can adjust the reaction rate for temperature using K2 = K1 Theta^(T2-T1) where Theta is usually on the order of 1.04 and K1 is the rate constant at temperature T1.

    A more thorough but difficult approach is to use our multi-species extension which enables you to more accurately model the reactions between chlorine, DBP's and precursors. You need to set up rate reaction equations for the interactions between the three (or more constituents) and determine the reaction constants for your water. This is only available for SELECTseries 5.

    Answer Verified By: Sushma Choure 

  • 0 Offline in reply to Tom Walski
    Thank you for your reply. Only one thing I would like further clarification: the equilibrium concentration. That would be the concentration that would result after a very long time of being analyzed for example. Can't we also use watercad to estimate this by running an EPS analysis for say 300 hours, and then graphing the concentration to see where the curve starts to approach "equilibrium? or level out"

    Thank you for your help,

    Liz
  • 0 Offline in reply to evstangelo
    The equilibrium concentration is an input property for the model. The concentration will approach whatever value you enter. The rate constant determines how quickly you will reach it.

    You need to do some laboratory or field testing to determine the value of that concentration.
  • 0 Offline in reply to Tom Walski

    You mentioned that you need WaterGEMS SELECTseries 5, can you perform it using WaterCAD as well?

    Thank you in Advance!

    Jacques Buzaglo

    Support and Sales Manager Bentley Products

    McKit Systems Ltd.

  • 0 Offline in reply to Jacques - McKit

    Hello Jacques, 

    Yes that's true you can perform the same using WaterCAD as well. 

    Here is difference between WaterCAD and WaterGEMS for your reference. 

    What is the difference between WaterCAD and WaterGEMS? 

    Also, here is wiki about modeling DBP formation in Water products. 

    Modeling DBP Formation - Water Quality Analysis 

    Regards,

    Sushma Choure

    Bentley Technical Suppport

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