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?