Calculation of TSS for continuity / Estimating MLSS

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?

No. According to the IWA report, the TSS in ASM2 is to be calculated as follows:
[b]TSS[/b] = i_TSS_X_I*(X_I)+i_TSS_X_S*(X_S)+i_TSS_X_BM*(X_H+X_AUT+X_PAO) [b]+ 3.23 * (X_PP) + 0.6 * (X_PHA) + (X_MEOH) + (X_MEP)[/b]

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.

Thank you :) That helped a lot. I will compute the TSS according to the equation in the ASM2 report.

Sorry to revive this old thread but it's directly related.

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

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

[list]
[li]First screenshot. Just to show you the sample layout. Look at ASU_Aero and Multi_BioOut which should be measuring the very same values.[/li]
[li]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.[/li]
[li]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?[/li]
[/list]

(The next screenshots, as only four are allowed in each post)

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.

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:
[list]
[li]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, [i][u]TSSc should be made fully coherent through all the model[/u][/i]).[/li]
[li]X_TSS. Pure ASM2 account which could be, (will be), different from TSSc because only [i]variations[/i] 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.[/li]
[/list]

(Just my two cents...)

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.

Hi, sorry to undig an old thread but I really think my following question/discussion nicely fits here.

As a summary: [b]I don't understand why i_[color=red]T[/color]SS_xxx factors in ASM2d model are not actually called i_[color=red]V[/color]SS_xxx (although VSS are also TSS), and I don't understand the high default values they have[/b]. I'll do my best to explain the issue.

Unless I'm VERY wrong, we can asume TSS = ISS + VSS, where ISS are inorganic/inert SS (like phosphorus precipitates or reagents or other inorganic colloidal substances), and VSS are carbonaceous/biological SS which disappear in an oven. Therefore, COD related SS are approximately just VSS.

In ASM1 there's actually no fine TSS modelization. ASM1 only cares about COD and, therefore, at the end, there's an i_TSS_COD conversion factor, (well it's really called F_TSS_COD in WEST), to roughly estimate TSS from COD. Ok, I understand it: this F_TSS_COD factor has to aggregate ISS and VSS from COD as a whole, even though ISS are not directly related to COD. That global F_TSS_COD factor is set at a default value of 0.75 gSS/gCOD.

But ASM2d model introduces X_TSS for better SS control as shown in the previous posts of this thread.

ISS don't change through the plant by their own definition, but only because of precipitation, dissolution or addition of substances related with phosphorus cycle (changes in X_PP, X_MEOH or X_MEP, and, well, X_PHA which is in fact VSS not ISS).

Forgetting about those P related ISS changes, the only part of TSS which changes through the plant is the VSS one related to COD. Therefore my first question: [b]shouldn't those i_TSS_xxx factors be called i_VSS_xxx in order to make things clearer?[/b] (And yes, VSS are also TSS, so the TSS names are not strictly wrong).

[b]And then the most important question[/b]. Through all the bibliography I've found there's a consensus about a COD/VSS relation close to the theorical 1.42 gCOD/gSS derived from a synthetic C5H7O2N formula for biomass, (in some books I've found slightly higher values: around 1.5). More over, 1.42 gCOD/gSS is the default value WEST uses in its own F_COD_VSS conversion factor. [b]But 1.42 gCOD/gSS is 0.70 gSS/gCOD[/b], quite lower than the default 0.9 gSS/gCOD used in i_TSS_BM, (and slightly higher values would mean even lower gSS/gCOD ones, as example: the 0.6 gSS/gCOD used for X_PHA). Even i_TSS_X_I and i_TSS_X_S, both set at 0.75 gSS/gCOD, are higher than that 0.70 gSS/gCOD reference. [b]So, isn't there [u][i]too much[/i][/u] X_TSS change in ASM2d related to X_COD changes when using the default values?[/b] Am I missing anything else here?