“Grit chamber” block in Modelica

Hi Enrico and Fabio,

Please, let me ask a question about the new “grit chamber” block in Modelica. Using the ASM1 model (as the simplest one), in Parameters/Group Settling, it is said that the factors “e_inorg” and “e_org” affect the settleable fraction of [b]inorganic [/b]and [b]organic [/b]components respectively.

• In the mentioned case of the ASM1 (or even in the ASM2dMod), where there are not inorganic components, I understand that the “e_inorg” parameter does not affect the influent characteristics, does it?

• In the mentioned case of the ASM1 (or even in the ASM2dMod), does the “e_org” parameter affect all the particulate components (XS, XBH, XI and XP)? Which makes me doubt is why, in that case, the description is not something like: "affects the seattleable fraction of [b]particulate [/b]components", as it is written in the "Screen" block...maybe I am wrong somewhere.

• Maybe the grit chamber block does not work with the ASM1/ASM2d models and only with the new ASM2dISS….that would be my main question

Thanks a lot!

Héctor

Hello Hector,
in the grit chamber model, the e_inorg fraction of inorganic portion (xi) of the particulate components is removed along with the e_org fraction of the organic portion (1 - xi).
The calculation of xi is ASM-specific - see image.
Hope this helps.

Thank very much for your answer, Enrico.

I understand it better, but I still have a doubt. Does the parameter “e_org” reduces the value of the COD after the grit chamber? The “e_inorg” factor obviously does not affect the COD, but the “e_org” I think that should do it, but I do not see in the exposed equations of your screenshot the relations to reduce the COD from “1-xi”…..

Thank you very much for your time.

Héctor

Hello Hector,
yes it does (should): by reducing the X_ components that contribute to the X_COD.
I made a calculation table (see image) to show what I mean: do you agree?

Almost…..sorry!! Regarding to the ASM1, I have simulated a simple influent that passes through a grit chamber. Using the default values I have tried to check, for the XI component, the mass balance, so the Underflow[X_I] is calculated by WEST and its value is 150.672 g/d (48.3846 g/d due to inorganic mass and 101.825 due to the organic mass (see “Export” file attached, where everything will be understood more clear)). However, if I try to calculate it though the different conversion factors and removal efficiency, I obtain the same value of the 48.3846 g/d due to inorganic mass (as WEST), but for the organic mass, my value is different to WEST (75.148 instead of 101.825). Could you please tell me where I am wrong?

Thank you very much.

Héctor

Hello Hector,
I added the actual calculation made in WEST to your spreadsheet.
I understand your calculation of ISS.
But you should not multiply by that factor: the i_COD_VSS factor already accounts for the conversion of the X components (COD units).

I can see it now. Thank you very much, Enrico.