Local Treatment

Removal of pollutants contained in the flow into a node can be modelled by assigning a set of treatment functions to the node. Treatment functions can be mathematical expression involving:

• Pollutant concentrations at the node inlet (use the pollutant name to represent a concentration)
• Removals of other pollutants (use R_ prefixed to the pollutant name to represent removal)
• Process variables which include:
  • FLOW for flow rate into node (user's flow units)
  • DEPTH for water depth above node invert (ft or m)
  • AREA for node surface area (\(ft^{2}\) or \(m^{2}\))
  • DT for routing time step (sec)
  • HRT for hydraulic residence time (hours).

The result of the treatment function can be either a concentration (C) or a fractional removal (R).

One may use the following math functions to build treatment expressions:

• abs(x) for absolute value of x
• sgn(x) which is +1 for x >= 0 or -1 otherwise
• step(x) which is 0 for x \<= 0 and 1 otherwise
• sqrt(x) for the square root of x
• log(x) for logarithm base e of x
• log10(x) for logarithm base 10 of x
• exp(x) for e raised to the x power
• the standard trig functions (sin, cos, tan, and cot)
• the inverse trig functions (asin, acos, atan, and acot)
• the hyperbolic trig functions (sinh, cosh, tanh, and coth)
• standard operators +, -, *, /, ^ (for exponentiation) and any level of nested parentheses.

For example, a first-order decay expression for BOD exiting from a storage node might be:

(8.6)   

while having the removal of some trace pollutant be proportional to the removal of total suspended solids (TSS) would be written as:

(8.7)   

Define local treatment conditions on the SWMM Local Treatment editor. The editor organizes data into the following groups:

• Identification: General identification information.
• Treatment Properties: Local treatment parameters.

 

Figure: The SWMM Local Treatment editor

Edit field	Description	Used or required by simulations	Field name in datastructure
ID	Local treatment setup ID	Yes	MUID
Description	Optional description for Local Treatment item	No	Description
Node ID	ID of Node where local treatment is performed	Yes	NodeID
Pollutant ID	ID of locally treated pollutant	Yes	PollutantID
Function	Treatment expression in terms of pollutant concentration (C) or pollutant removal (R), and using other standard variables and functions	Yes	Function

Table: Edit fields in the Local Treatment editor (mss_LocalTreatment)