The Canadian

Centre for Environmental Modelling and Chemistry

Sewage Treatment Plant (STP) Model

The STP or TORONTO model, written in BASIC, was created to estimate the fate of a chemical present in the influent to a conventional activated sludge plant as it becomes subject to evaporation, biodegradation, sorption to sludges and to loss in the final effluent. The most critical and uncertain variable is the biodegradation rate constant and its dependence on biomass concentration.

A number of chemicals are defined within the program or the user may define a new chemical. Default STP operating conditions or user-specified values may be used.

A more detailed description of this work can be found in

Environ. Sci. Technol. Vol. 29, p. 1488, 1995 by B. Clark, J.G. Henry, and D. Mackay.

The required input data are:
Chemical Properties:

  • chemical name
  • temperature
  • molecular mass
  • water solubility
  • vapour pressure
  • log Kow
  • biogradation data ie. half-lives in primary clarifier,
    aeration vessel, and final setting tank

    • STP Operating Conditions:

  • influent rate
  • influent VSS
  • fractional removal of VSS in primary sludge
  • VSS concentration in primary sludge
  • sludge recycle as fraction of influent
  • waste sludge as fraction of influent
  • MLSS concentration in aeration vessel
  • VSS concentration in effluent
  • air flow as multiple of aeration tank
  • chemical concentration in influent

    • STP Design Values:

  • primary clarifier area
  • primary clarifier depth
  • aeration tank volume
  • final clarifier area
  • final clarifier depth

    • Model output includes:

  • Z and D values
  • steady state phase concentrations
  • process stream fluxes
  • flow sheet
  • relative amounts of chemical that are likely to be
    stripped or volatilized, sorbed to sludge, biodegraded,
    and discharged in the effluent

    • System requirements to run the compiled program are minimal.

    Please read the STP SOFTWARE LICENSE before downloading the software. Use of the software constitutes your agreement to abide by the terms and conditions set out in the license agreement.

    Register to Download

    CEMC Home | General Information | Models | Experimental Facilities | Atmospheric Chemistry | Graduate Studies | Contact

    Last updated August 12, 2011.