### ASIM User Forum - [Constant rate of a precipeter in ASM2d]

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**From**: Laila Bahgat

**Date:** 08/02/2004

This question is not specifically related to WinAsim however
I'll very much appreciate any clarification regarding it:
Within my MATLAB ASM2d simulations I need to activate the 2
last equations of the model related to the chemical
precipitation of P through adding a constant rate of Xmeoh.
In a paper I reviewed lately it was written that a dosage
rate of 0.6 cubic meters/d equals 600 Kg Xmeoh/ d (although
I can't figure out how this comes) so here is what I did:
I took this weight equivalent or:
600 Kg Xmeoh/d = 600 * 1000 g Xmeoh/ d ÷ tank volume (say
1000 cubic meters) leading to 600 gm Xmeoh/ cubic meters*
day
so I added 600 to the derivative equation of Xmeoh of the
model and simulated the system.
Can someone please tell me if what I did was right or not
and how should this constant rate be represented?
By the way I have been told that it is erroneous to
represent the dosage rate using volume units i.e. 0.6 cubic
meters/ day since it should change as its chemical form
changes, so how come the paper refers to the dosage rate as
a volume and how did they relate this volume unit as equal
to the weight unit they mentioned?
Thank you very much.

**Reply #1**

**From**: Christian Abegglen (abegglen@ihw.baug.ethz.ch)

**Date:** 08/06/2004
In my opinion, the calculation of a precipitation rate from
a dosage rate is rather adventurous. The amount of Phosphate
precipitated depends on the amount of Metal added in mol or
grams. You can calculate that from the volume added, if you
know the metal concentration.
If you want to add a constant rate of MeOH, just add a
second influent with a constant flow rate and the required
Me-concentration.
Best regards
Christian Abegglen

**Reply #2**

**From**: laila bahgat

**Date:** 08/06/2004
Thank you for the clarification

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