Author Topic: Calculation of TSS for continuity / Estimating MLSS  (Read 742 times)

ivarurdalen

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Calculation of TSS for continuity / Estimating MLSS
« on: May 25, 2015, 04:44:16 pm »
Hi. I have a problem of understanding the calculation of the variable X_TSS in the ASM2d model in the WEST software.

My understanding was that the this was the correct equation to calculate the X_TSS

X_TSS = i_TSS_X_I*(X_I)+i_TSS_X_S*(X_S)+i_TSS_X_BM*(X_H+X_AUT+X_PAO).

But for my setup I get for the anaerobic tank:
X_PAO = 1571
X_H = 1011
X_AUT = 20
X_I = 1152
X_S = 91
i_TSS_X_I, i_TSS_X_S = 0.75
i_TSS_X_BM = 0.9

State variable in WEST: X_TSS = 2035
My calculation according to the equation above:  X_TSS = 3256

Is this the correct thinking or am I misunderstanding?

How can I estimate the MLSS based on the ASM2d components? Is it sufficient to use the X_TSS state variable?

Enrico Remigi

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #1 on: May 26, 2015, 12:55:22 pm »
No. According to the IWA report, the TSS in ASM2 is to be calculated as follows:
TSS = i_TSS_X_I*(X_I)+i_TSS_X_S*(X_S)+i_TSS_X_BM*(X_H+X_AUT+X_PAO) + 3.23 * (X_PP) + 0.6 * (X_PHA) + (X_MEOH) + (X_MEP)

So your calculation is essentially correct (except these additional terms).
It's a known issue that in ASM2(d) the "component" X_TSS and the algebraic state variable TSS (combination of other components, according the equation above) are redundant and in fact de-coupled. In other words, X_TSS evolves independently from its elementary components - which can evidently result in these discrepancies.

The safest way to compute TSS is therefore using the equation above.
Enrico U. Remigi
Wastewater Process Modeller
DK Urban
Kortrijk (Belgium)

ivarurdalen

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #2 on: May 30, 2015, 11:06:17 am »
Thank you :) That helped a lot. I will compute the TSS according to the equation in the ASM2 report.

arspr

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #3 on: February 28, 2020, 09:00:26 am »
Sorry to revive this old thread but it's directly related.

I'll explain in a momment but the summary is ASU tanks don't seem to follow that formula in Multiprobe sensors do. Why? (A possible bug?) (Other reason?)

I'm going to post some screenshots to show the issue.

  • First screenshot. Just to show you the sample layout. Look at ASU_Aero and Multi_BioOut which should be measuring the very same values.
  • Second to fourth screenshots. Multi_BioOut ones. TSSc is 4587.52 g/m3 and I can confirm that it strictly follows the previously posted formula.
  • Fifth to seventh screenshots. ASU ones. TSSc is 4618.06 g/m3 despite all C() and i_TSS_xxx values remain unchanged, (as expected). What's happening?

arspr

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #4 on: February 28, 2020, 09:01:53 am »
(The next screenshots, as only four are allowed in each post)

Enrico Remigi

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #5 on: March 02, 2020, 11:01:54 am »
Hi,
yes, I understand the confusion generated by the symbol "TSSc".
All you should consider is TSS both in the tank and in the sensor, i.e. "C(X_TSS)" (algebraic state variable) and TSS (sensor) for the tank, and "y_TSS" (sensor) for the multi-probe sensor.
According to your screenshots, those consistently show 4,588 g/m3 - which is the correct value.

"TSSc" is some other calculation, that, in retrospect, should not even be exposed through the GUI.
Thank you for pointing it out - will fix it asap.
Enrico U. Remigi
Wastewater Process Modeller
DK Urban
Kortrijk (Belgium)

arspr

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #6 on: March 02, 2020, 01:45:29 pm »
Many thanks for your answer, I therefore dismiss TSSc at least in ASUs.

Nevertheless, maybe you should keep TSSc. I'll try my best to clearly explain it (English is not my mother language).

In ASM1, TSS is just a "secondary" variable, it is not inside the model. It's just a scalation from total X_COD through F_TSS_COD.

In ASM2, TSS is inside the model but it's somehow a secondary variable nevertheless. It doesn't actually do anything "relevant". ASM2 just keeps an account of its variations from its initial value based on X_COD changes (and phosphorus components) through the formula you gave before. So maybe having two different estimations might be useful:
  • TSSc. The formula you posted. Pure scalation from X_COD (and phosphorus components). In a way, fully equivalent to TSS in ASM1 although with just a more complex formula. (But of course, TSSc should be made fully coherent through all the model).
  • X_TSS. Pure ASM2 account which could be, (will be), different from TSSc because only variations are calculated by that formula. Initial value X_TSS0 is "fixed", and quite possibly X_TSS0 is not equal to TSSc(X_COD0 & X_phosphorus0). This value could be useful if somewhow you detect your plant has a high inorganic influent component X_TSS but you don't want to change biomass to TSS ratios because they are "fully" accurate.

(Just my two cents...)

Enrico Remigi

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Re: Calculation of TSS for continuity / Estimating MLSS
« Reply #7 on: March 02, 2020, 01:55:14 pm »
I completely agree, of course.
What I actually meant was: I will first make sure that TSSc is meaningful and properly described both in the GUI and in the Models Guide (to avoid confusion); if it should prove to be unnecessary (because in ASM1, the variable TSS is effectively a COD-based, calculated TSS; and in ASM2, TSS could be made into the same COD-based calculation and not just a duplicate of X_TSS), I would prefer to remove TSSc altogether.
Enrico U. Remigi
Wastewater Process Modeller
DK Urban
Kortrijk (Belgium)