Hi, and yet another experiment in my training with WEST.
I've modeled the very same sample plant in ASM1Temp and ASM2dModTemp with the very same influent (same flow, same COD, same N, same fractionation). And I've adjusted ALL kinetic, composition and stoichiometric parameters in ASM2d to make it fully equivalent to ASM1.
More over, as I don't actually care about phosphorus, I've set S_A to 0 in influent (therefore ASM1 S_S is fully equivalent to ASM2d S_F) and an extremely low fermentation rate (Q_fe = 0.0001) effectively killing PAO generation as there's just residual S_A generation.
More over, as ASM1 doesn't have different decay ratios in aerobic or anoxic conditions, I've set all ASM2d n_NO_xxx_d ratios to 1. (I hope effectively kiling ASM2d[b][u]Mod[/u][/b]Temp feature as Enrico confirmed here: https://forum.mikepoweredbydhi.com/index.php/topic,21895.0.html ).
And of course every dimension in tanks and flows through the plant are exactly the same (Anoxic tank [b]100 m3[/b], Aerated tank [b]350 m3[/b], influent [b]500 m3/d[/b], SST down flow [b]510 m3/d[/b] with [b]f_ns = 0.005[/b], excess of sludge [b]6 m3/d[/b] -external recycle is 504 m3/d-, internal recycle [b]1500 m3/d[/b], DWU flow [b]1.1 m3/d[/b] with [b]e_X = 0.96[/b] and Centrifuge flow [b]0.16 m3/d[/b] with [b]e_X=0.96[/b]). Aerated tank is working at [b]1.5 g_O2/m3[/b] in both models.
And as I'm not analizing temperature behaviour, I've also set T=20ºC. I'm running a steady simulation for 200 days in order to get that, the steady stabilized result.
Well, the results are similar but with some key differences. And I cannot understand why they are happening.
[b]1. The "missing" ammonification reaction in ASM2d which leads to less TKN in effluent[/b]
This is the "only" difference I can explain. ASM1 has independent lysis cycles in COD and N and, because of the low rate in the ammonification reaction, there's quite noticeable amount of N entrapped in S_ND at the end, which is "useless" for biological growth. Therefore TKN in effluent is higher in ASM1 than in ASM2d. I've even set the k_a rate in ASM1 at its maximum possible value (0.25, this is the [i][u]ONLY[/u][/i] change I've made to ASM1 default values), but it cannot compensate the low S_ND generated/accounted for in ASM2d from its residual S_F and i_N_S_F values.
[b]2. Greater amount of biomass in ASM2d which I just cannot understand[/b]
This is, I think, the key difference which probably generates the rest of them. (As example smaller S_NH in effluent in ASM2d because there's more active nitrification biomass).
Looking at Multi_BioOut the values I get are:
[list]
[li]ASM1[list]
[li]X_BH = 1404.6 g/m3[/li]
[li]X_BA = 79.7 g/m3[/li]
[/list][/li]
[li]ASM2d[list]
[li]X_H = 1643.7 g/m3[/li]
[li]X_AUT = 91.8 g/m3[/li]
[/list][/li]
[/list]
And I swear every single growth, decay and lysis rates, halfsaturation coefficients, growth yields, whatever, are exactly the same ones in both models. More over, ASM2d has alkalinity "switches" in both heterotrophic and autotrophic growths which might cause even smaller growths, not a greater ones. (I've checked it n times).
[i][b][u]So, please, could any one spend some time analyzing and explaining what's going on?[/u][/b][/i] (I mean what I'm doing wrong) I upload WEST reports for both plants with the key elements, but if you need/want the full built models, or any other further info, I can provide them through OneDrive, or zipping and attaching the key files you tell me.
Thanks in advance.
