The Treatment Editor allows you to specify the treatment of the project's pollutants.

Removal of pollutants from the flow streams entering any drainage system node is modelled by assigning a set of treatment functions to the node. A treatment function can be any well-formed mathematical expression involving:

• The pollutant concentration of the mixture of all flow streams entering the node. Use the pollutant name to represent a concentration.

• The removals of other pollutants. Use R_ prefixed to the pollutant name to represent removal.

• Any of the following process variables:

• • Flow for flow rate into node (User-defined flow units).

  • Depth for water depth above node invert (m or ft).

  • Area for node surface area (mı or ftı).

  • 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)

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

See Also SWMM Node Data Runoff