Modelling WWTP to evaluate the influence of stormwater

Dear MikebyDHI

I’m using ASM2d to model WWTP with the aim of evaluating the influence of stormwater contribution

Primary Clarifier

I dragged primary clarifier (PST_1) from separation block library, there is only Q_flow (m3/d) box to fill in the value. I was expecting to find boxes for area or volume to fill in values as well. Is there something wrong I have done in selecting primary clarifier?

Aeration basins

I want to control SRT with the aim of achieving sufficient nitrification. Oxygen level should be controlled by ammonium feedback and set point should vary between 1 to 2mg/l. I have read all your previous comment to Tanya but I have two aerated zones which I represented them in the model as two different tanks in series. How should I do it?

Sand Filter

The sand filter is aimed to remove P by using Fe compound. The sand filter has parameters such as area (A), height (m) and backwash. The backwash box has no unit while data I have for backwash flow rate has unit in m3/s. What should I do to make sure that the model recognize the backwash flow unit?

Also, I want to manipulate filtered flow and unfiltered flow. The variable I have are Q_backwash, Q_In, Q_out_filtered, Q_out_unfiltered,  X_backwash, X_In,  X_out_Filtered, X_out_unfiltered and H.  I have read your comment to Hjrey but the equation does not include particulate (X). I want to include on/off function i.e. when Q_out_filtered flow is zero the Q_backwash pump should start and when it stop the flow should start passing through the sand filter. How can I do it by using my variable parameters?

Thanks in Advance.
Moses

Hi Moses,

I don't know the standard settings of WEST by hard but here are some comments.

Primary Clarifier
the available parameters will depend on the model you have selected for the primary clarifier. The difference between the models is usually the complexity. for simple models you usually only have a few parameters.

Aeration basins
I'm not sure what you mean here. but try to mimic the control as it is (or as you want it to be). I.e. if you measure in one tank and control aeration in both than use one controller with one input and two outputs, if you use two measurements and separately control the aeration in both tanks than use two controllers with each one input and one output.

Sand Filter
Keep in mind here that the sand filter model describes only the sand filtration. If you want to model P removal due to iron dosing in combination with a sand filter, than you have to add the chemical dosing and mixing units before the sand filter

[quote]Primary Clarifier
the available parameters will depend on the model you have selected for the primary clarifier.[/quote]
Depending on the model you select for the specific block (this is evidently true for any block, not just for a PST) in the Properties pane (prop: [b]ClassName[/b]), the parameters (and variables) displayed in the Block Details pane will be different. For instance, if you select the "PrimaryTakacs", you will need to indicate, the surface and average depth of the settling tank.

[quote]I want to control SRT with the aim of achieving sufficient nitrification. Oxygen level should be controlled by ammonium feedback and set point should vary between 1 to 2mg/l.[/quote]
Maybe I misunderstand: but maintaining a constant DO by means of a "cascade" control logic (the ammonium controller on the effluent regulates the DO set-point of the aeration controller) is, or may be, independent from a SRT controller (which may, for instance, regulate the sludge wastage based on the desired SRT).
The first type of logic may consist of an On-Off controller for ammonium followed by a PI controller for DO. The second, may be a PI controller for the flow rate of sludge wastage based on the computed SRT.

As Youri pointed out, the inclusion of biological processes in a Sand Filter may be tricky.
The suggested solution of "coupling" the Sand Filter to a mixing tank which a) receives the iron dosage and b) hosts the biological reactions may be the easiest.

Dear Enrico and Youri
Thanks for your assistance. I have succeeded all except sand filter part.
There is group operational parameter 'backwash' which is unit less. which value should I put there? my backwash pump capacity is 0.33 m3/s.

I want to start operate backwash once the sand filter is clogged. what equation should I use based on sand filter parameters and how to incorporate it in the model?

Thanks
Moses

The "[b]Backwash[/b]" you see as (interface) input variable is in fact a switch (i.e. backwashing state): 0 or 1 for non-backwash and backwash phase respectively.
What you could do is connect this to a timer, in order to switch backwashing on/off. And synchronise this with the other interface input variable, "[b]Inflow_Backwash[/b]" that is to receive your backwash flow (and composition, i.e. the usual ASMx state vector) [u]precisely[/u] during the backwashing phase.

Dear Enrico and Youri

I have connected timer and buffer tank (u1 to Q_pump) and then I connect buffer tank to sand filter (pumping Energy to backwash). Am I right for what I have done?
There is parameters at the timer (T1, T2, u11 and u12). how can I set this parameters?. I'm also wondering on how to include variables in that flow scheme to get on/off backwashing?
Regards
Moses

Your association PumpingEnergy <-> Backwash is definitely wrong, because a) the two quantities have different units and b) Backwash is an integer, limited between 0 and 1.

One option would be:
[list]
[li]use a Timer22, i.e. 2 phases and 2 outgoing signals[/li]
[li]link one signal (u1) to the pump flow rate of the buffer tank (I am assuming you're using the pump for back-washing)[/li]
[li]link the other signal (u2) to the "Backwash" (interface variable) of the sand filter[/li]
[/list]

In a timer model with 2 phases, T1 and T1 indicate the length of each phase, e.g. 10 h and 10 min.
In a timer model with 2 phases and 2 outgoing signals, u11, u12, u21 and u22 indicate the values of the first and second outgoing signals during the first and the second phase respectively.

Thanks Enrico
Much appreciated
Moses