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Pollutograph Mass Conversion Factor

Using SewerGEMS Connect Edition 10.02.04.53

Hi,

I am trying to set up pollutographs to manholes and am using the mass rate type.

What is the "Mass Units Conversion Factor" on the pollutograph, and does it have to be a non-zero value?

I am getting errors while using the mass rate pollutograph combined with hydrograph loading on a manhole and I'm wondering if the error is coming from this mass units conversion factor.

Thanks in advance!

Maria Blake

  • Hello Maria,

    What error messages are you seeing? That may help with this issue.

    Regards,

    Scott

  • Regarding the Mass Units Conversion Factor, below is the definition from the EPA-SWMM documentation. We will seek to include this in our Wiki knowledgebase if you find it helpful:

    Units Factor

    A numerical factor used to convert the units of pollutant mass flow rate into concentration mass units per second. For example, if the inflow data were in lbs/day and the pollutant concentration was chosen as mg/L, then the conversion factor value would be (453,590 mg/lb) / (86,400 sec/day) = 5.25 (mg/sec) per (lb/day). This field does not appear for FLOW inflow, and for concentration-type inflows any value entered will be overriden to 1.0.

    More than one constituent can be edited while the dialog is active by simply selecting another choice for the Constituent property. However, if the Cancel button is clicked then any changes made to all constituents will be ignored.

    • If a pollutant is assigned a direct inflow in terms of concentration, then one must also assign a time series inflow to flow, otherwise no pollutant inflow will occur. An exception is at submerged outfalls where pollutant intrusion can occur during periods of reverse flow. If pollutant inflow is defined in terms of mass, then a corresponding flow inflow is not required.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

  • Hi Jesse, thank you for the information, it is very helpful.

    I would like to confirm my understanding of how SewerGems interprets the units factor. 

    My inflow data is in kg/day and my chosen concentration is mg/L. The conversion factor would be (1000000 mg/kg) / (86400 sec/day) = 11.574 (mg/sec) per (kg/day)?

    Thanks,

    Maria Blake

  • What you are doing sounds as if it meets the requirements of the explicit SWMM solver.

    The example given in the SWMM manual is for English units so it's difficult to tell which units mass flow are supposed to be. The original SWMM manual is not clear on this.

    The underlying equation is

    M = Q x C

    Where M = mass flow rate, Q = flow and C = concentration.

    A good check is to do a hand calculation where you know Q and C and calculate M. Then run it through SWMM and see if the results agree. 

  • Note that I have added some information based on this discussion to the following related Wiki article: Prediction of quality characteristics of sewers


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.