Author Topic: Exact meaning of "Mod" in ASM2dModTemp, (lysis dependant on electron acceptor)  (Read 650 times)

arspr

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I would like to ask which exact modification "Mod" means over ASM2d.

In the help file, it basically says "Lysis of -whatever- depends on the electron acceptor", but it gives no further insight.

I've also noticed there are three added reduction parameters over pure ASM2d (n_NO_AUT_d, n_NO_Het_d  and n_NO_P_d). Therefore my either wild or educated guess is that WEST is basically changing the rate for the lysis/decay reactions, (as example in heterotrophs), from just b_H · X_H to b_H · X_H · ( S_O/(K_O + S_O) + n_NO_Het_d · K_O/(K_O+S_O) ). I mean, when there's no free oxygen, (anoxic and also anaerobic tanks), the decay rate would be 50% of the "normal" aerobic one, (because n_NO_Het_d = 0.5).

Am I right? Is this the change made by ASM2dMod over ASM2d? Is it another one?
« Last Edit: February 28, 2020, 05:33:48 pm by arspr »

Enrico Remigi

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Totally correct: the modification is indeed in the rate expression of those biomass decay processes
Enrico U. Remigi
Wastewater Process Modeller
DK Urban
Kortrijk (Belgium)

arspr

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Oooops. I don't know if intended but maybe you have a bug here.

Look at the screenshot I post from Model Editor. You have a NO Monod switch on lysis rate. Therefore you are saying there's no lysis in anaerobic conditions...

I mean, what I guessed was: b_H · X_H · ( S_O/(K_O + S_O) + n_NO_Het_d · K_O/(K_O+S_O) )

But what you actually have is:  b_H · X_H · ( S_O/(K_O + S_O) + n_NO_Het_d · K_O/(K_O+S_O) · S_NO/(K_NO+S_NO))

FaPo

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The process rate equation for lysis that is currently implemented (with switching function for S_NO) derives from the original model implementation, on which ASM2dModTemp is based. You can find more information in Gernaey and Jørgensen (2004).

On a separate note, this process rate equation described a slower decay under anoxic/anaerobic conditions. This may be the reason why you have obtained higher MLSS concentrations using ASM2dModTemp in your model comparison exercise, and have subsequently increased the parameter value for b_H and b_AUT in order to obtain similar MLSS, X_H and X_AUT concentrations using ASM2dModTemp and ASM1Temp.

  • Decay/Lysis is slower in WEST ASM2d implementation. But I've been able to more or less compensate it with higher b_H (0.69 vs original 0.62) and b_AUT (0.1675 vs original 0.15) values.
« Last Edit: March 18, 2020, 08:53:58 pm by FaPo »

arspr

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Please, forget about my models here.

Just check if it is correct or not that there's actually no lysis under anaerobic conditions. Not just slower, but none at all. If that is what you desire, it's perfect. There would be a bug otherwise.

FaPo

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As you point out, the ASM2dModTemp formulation assumes negligible lysis/decay under ideal anaerobic conditions.
For heterotrophs, for instance, the model considers no net growth under anaerobic conditions since: (i) anaerobic hydrolysis and fermentation do not result in any growth; (ii) lysis/decay is negligible.

In a full-scale system modelled ASM2dModTemp, the anaerobic lysis/decay may not necessarily be null - very low (but not null) S_NO levels may in fact occur in the anaerobic tank depending on the nitrate load being recirculated with the RAS stream.

If you wish to update the current model formulation with a modified expression for the decay rate, you can use the Model Editor and change the expression to:
- b_H · X_H · (S_O/(K_O + S_O) + n_NO_Het_d · K_O/(K_O+S_O))             [assuming that aerobic decay > anoxic decay = anaerobic decay]
- b_H · X_H · (S_O/(K_O + S_O) + n_NO_Het_d · K_O/(K_O+S_O) · S_NO/(K_NO+S_NO) + n_anaer_Het_d · K_O/(K_O+S_O) · K_NO/(K_NO+S_NO))             [assuming that aerobic decay > anoxic decay > anaerobic decay]
« Last Edit: March 23, 2020, 04:14:00 pm by FaPo »