Adding Treatment to a Node

You can model the removal of pollutants from the flow entering any drainage system by assigning treatment functions to the node. In Drainage and Utilities, you assign treatment functions to a node by adding a treatment collection, which contains one or more pollutants and their associated treatment expressions.

A treatment expression involves the pollutant concentration of the mixture of all flow streams entering the node (use the pollutant name to represent a concentration), or the removal of other pollutants (use R_ prefixed to the pollutant name to represent removal).

Treatment expressions have the general form:

R = f(P, R_P, V)

C = f(P, R_P, V)

Where:

R = fractional removal

C = outlet concentration

P = one or more pollutant names

R_P = one or more pollutant removals, (add R_ to the front of the pollutant name)

V = one or more of the following process variables:

FLOW for flow rate into node (in user-defined flow units)
DEPTH for water depth above node invert (ft or m)
AREA for node surface area (ft2 or m2)
DT for routing time step (sec)
HRT for hydraulic residence time (hours)

The result of the treatment function can be either a concentration (denoted by the letter C) or a fractional removal (denoted by R). For example, a first-order decay expression for BOD exiting from a storage node might be expressed as:

C = BOD * exp(-0.05*HRT)

or the removal of some trace pollutant that is proportional to the removal of total suspended solids (TSS) could be expressed as:

R = 0.75 * R_TSS

To add a treatment collection to a node:

Note: Make sure you set the Engine Type to Explicit (SWMM 5) in the Calculation Options for your model before computing results.

Add a node to your model or select an existing node, then display the Property Editor for the node (double-click the node or press F4).
In the SWMM Extended Data section of the Property Editor, set Apply Treatment? to True. The Treatment field becomes available.
Click the Ellipses (...) button in the Treatment field (where "<Collection: 0 items>" is displayed) to display the Treatment Collection dialog box.
The Treatment Collection dialog box displays each pollutant and its associated treatment expression as a row in a table. Click the New button to add a row to the table.
Click in the Pollutant field, then select an existing pollutant from the drop-down menu, or click the Ellipses (...) button to display the Pollutants dialog box, where you define pollutants in your model.
Type a treatment expression in the Treatment column.
Repeat Steps 4 - 6 for each pollutant you wish to add to the treatment collection.
Click OK to close the dialog box and add the collection to the node.

Treatment Collection Dialog Box

The Treatment Collection dialog box lets you add multiple pollutants and their associated treatment expressions to a node for the purpose of removing pollutants in your model. You access this dialog box from the SWMM Extended Data section of the Property Editor for the selected node.

The dialog box contains the following toolbar buttons:

New	Adds a new row to the Pollutants table. Click in the row to select an existing pollutant from the drop-down menu, or click the Ellipses (...) button to define new pollutants.
Delete	Deletes the current row from the table.
Report	Lets you view a report of the collection.

The dialog box also contains the following controls:

Column	Description
Pollutant	Lets you add a pollutant to the collection. Click the down-arrow to select an existing pollutant from the drop-down menu, or click the Ellipses (...) button to define new pollutants.
Treatment	Lets you type a valid treatment expression to the pollutant.