SimpleTreat

Sewage Treatment Plant Model
Fact Sheet

Source: Commission modelling inventory and knowledge management system (MIDAS)

Date of Report Generation: Thu Mar 06 2025

Dissemination: Public

© European Union, 2025

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Overview

Acronym

SimpleTreat

Full title

Sewage Treatment Plant Model

Main purpose

SimpleTreat 4.1 is an exposure and emission model developed to estimate chemical emission from sewage treatment plants and exposure in surface water within the framework of risk assessment of chemicals. The current version is a revision of SimpleTreat 4.0.9, please see the release note for details. SimpleTreat 4.0 and 4.1 are both updates of SimpleTreat 3.1, which supported the chemical act 30 years ago in the Netherlands and later in the European Union (EU). The revision from v4.0 to v3.1 was necessary to account for more recent scientific insights with respect to behavior of chemicals in domestic sewage and activated sludge.

Summary

SimpleTreat was developed to enable calculation of the fate of organic chemicals in a biological wastewater treatment plant (WWTP) ecosystem.

The model is a steady state, multiple box model solving the mass balance of a contaminant taking into account phase partitioning, degradation and volatilization. The model estimates concentrations of contaminants in effluents and sludge, and the corresponding discharges through air (volatilization), solid and liquid discharges from the plant.

The model is designed to appraise the environmental fate of a chemical undergoing treatment in a WWTP. It can be used in regulatory applications as well as in the assessment of policy scenarios of wastewater treatment.

Model categories

HealthEnvironment

Model keywords

wastewaterchemicalsdegradationphase partitioningeffluentssludge

Model homepage

https://www.rivm.nl/en/soil-and-water/simpletreat

Ownership and Licence

Ownership

Third-party ownership (commercial companies, Member States, other organisations, …)

Ownership details

Dutch National Institute for Public Health and the Environment (RIVM)

Licence type

Non-Free Software licence

The license has one or more of the following restrictions: it prohibits creation of derivative works; it prohibits commercial use; it obliges to share the licensed or derivative works on the same conditions.

Details

Structure and approach

The model assumes steady state and complete mixing of the contaminant in the compartments of a WWTP. It assumes partitioning to follow linear isotherms. The description has limitations on validity for ionic and polar compounds. The mass balance of a contaminant in the various phases and compartments within the WWTP is solved as a system of linear equations.

Input and parametrization

  • Physicochemical properties of the contaminant:
    • Air-water partition coefficient
    • Degradation rate
    • Solids/water partition coefficient
  • Operating conditions of the WWTP (particularly the hydraulic loading rate and sludge retention time).

Main output

  • Concentration of the contaminant in the different compartments and phases of the WWTP, including sludge and effluents.
  • Percentage of the contaminant mass in the effluents that ends up in the sludge and effluents, and degradation/volatilization removal efficiency (%).

Spatial & Temporal extent

The output has the following spatial-temporal resolution and extent:

ParameterDescription
Spatial extent / country coverage
The model is generic and can be applied to a WWTP in any location. The model is not spatially explicit (the WWTP is represented as a set of interconnected boxes).
Spatial resolutionOther
Not spatially explicit
Temporal extentOther
Steady state
Temporal resolutionOther
Steady state models can be applied independent of time. They refer to the time for which inputs are valid.

Quality & Transparency

Quality

Model uncertainties

Models are by definition affected by uncertainties (in input data, input parameters, scenario definitions, etc.). Have the model uncertainties been quantified? Are uncertainties accounted for in your simulations?

not applicable
The model is known to be sensitive to certain parameters. No formal sensitivity/uncertainty analysis available.

    Sensitivity analysis

    Sensitivity analysis helps identifying the uncertain inputs mostly responsible for the uncertainty in the model responses. Has the model undergone sensitivity analysis?

    not applicable
    The model is known to be sensitive to certain parameters. No formal sensitivity/uncertainty analysis available.

      Have model results been published in peer-reviewed articles?

      yes

        Has the model formally undergone scientific review by a panel of international experts?

        Please note that this does not refer to the cases when model results were validated by stakeholders.

        no
        The model is scrutinized in the community of practitioners.

          Model validation

          Has model validation been done? Have model predictions been confronted with observed data (ex-post)?

          not applicable
          The model has been applied mostly in a regulatory context. Comparison with observed data requires parameter calibration.

            Transparency

            To what extent do input data come from publicly available sources?

            This may include sources accessible upon subscription and/or payment

            Based on both publicly available and restricted-access sources

            Is the full model database as such available to external users?

            Whether or not it implies a specific procedure or a fee

            no

              Have model results been presented in publicly available reports?

              Note this excludes IA reports.

              yes

              For details please refer to the 'peer review for model validation' documents in the bibliographic references

              Have output datasets been made publicly available?

              Note this could also imply a specific procedure or a fee.

              no

                Is there any user friendly interface presenting model results that is accessible to the public?

                For instance: Dashboard, interactive interfaces...

                yes
                The model comes in a format like a spreadsheet.

                  Has the model been documented in a publicly available dedicated report or a manual?

                  Note this excludes IA reports.

                  yes

                  Is there a dedicated public website where information about the model is provided?

                  yes

                  Is the model code open-source?

                  no

                  Can the code be accessed upon request?

                  no

                  The model’s policy relevance and intended role in the policy cycle

                  The model is designed to contribute to the following policy areas

                  • Environment
                  • Public health

                  The model is designed to contribute to the following phases of the policy cycle

                    The model’s potential

                    The model can be used to appraise the fate of a chemical undergoing wastewater treatment. This may have obvious, important policy and regulatory implications.

                    Previous use of the model in ex-ante impact assessments of the European Commission

                    Use of the model in ex-ante impact assessments since July 2017.

                    2022
                    SWD/2022/541 final

                    Impact Assessment accompanying the document Proposal for a Directive of the European Parliament and of the Council concerning urban wastewater treatment (recast)

                    Lead by
                    ENV
                    Run by
                    European Commission
                    Contribution role
                    baseline and assessment of policy options
                    Contribution details

                    SimpleTreat was used to estimate the contribution made by the existing WWTPs to the reduction of chemical pollution (not a target of the Urban wastewater treatment directive 91/271/EEC)

                    Bibliographic references

                    Studies that uses the model or its results

                    No references in this category

                    Peer review for model validation

                    European scale assessment of the potential of ozonation and activated carbon treatment to reduce micropollutant emissions with wastewater 

                    Published in 2022
                    Pistocchi, A., Alygizakis, N. A., Brack, W., Boxall, A., Cousins, I. T., Drewes, J. E., Finckh, S., Gallé, T., Launay, M. A., McLachlan, M. S., Petrovic, M., Schulze, T., Slobodnik, J., Ternes, T., Van Wezel, A., Verlicchi, P., & Whalley, C. (2022). European scale assessment of the potential of ozonation and activated carbon treatment to reduce micropollutant emissions with wastewater. Science of The Total Environment, 848, 157124. https://doi.org/10.1016/j.scitotenv.2022.157124

                    Model documentation

                    SimpleTreat 4.0: a model to predict fate and emission of chemicals in wastewater treatment plants: Background report describing the equations. RIVM Report 601353005. RIVM, Bilthoven The Netherlands

                    Published in 2014
                    Struijs J (2014) SimpleTreat 4.0: a model to predict fate and emission of chemicals in wastewater treatment plants: Background report describing the equations. RIVM Report 601353005. RIVM, Bilthoven The Netherlands

                    Other related documents

                    No references in this category