Wastewater treatment plants are large non-linear systems subject to large perturbations in flow and load, together with uncertainties concerning the composition of the incoming wastewater. Nevertheless these plants have to be operated continuously, meeting stricter and stricter regulations.

Many control strategies have been proposed in the literature but their evaluation and comparison, either practical or based on simulation is difficult. This is partly due to the variability of the influent, to the complexity of the biological and biochemical phenomena and to the large range of time constants (from a few minutes to several days) but also to the lack of standard evaluation criteria (among other things, due to region specific effluent requirements and cost levels).

It is difficult to judge the particular influence of the applied control strategy on reported performance increase, as the reference situation is often most suboptimal. Due to the complexity of the systems it takes much effort to develop alternative controller approaches, so that seldomly a fair comparison between different options is made. And even if this is done, it remains difficult to conclude to what extent the solution is process or location specific.

To enhance the acceptance of innovating control strategies the evaluation should be based on a rigourous methodology including a simulation model, plant layout, controllers, performance criteria and test procedures.

From 1998 to 2004 the development of benchmark tools for evaluating by simulation, control strategies for activated sludge plants. The benchmark development has then being undertaken in Europe by Working Groups of COST Action 682 and 624. This work is now continued under the umbrella of an IWA Task Group.

The benchmark is a simulation environment defining a plant layout, a simulation model, influent loads, test procedures and evaluation criteria. For each of these items, compromises were persued to combine plainness with realism and accepted standards. Once the user has validated the simulation code, any control strategy can be applied and the performance can be evaluated according to certain criteria.

The benchmark is not linked to a particular simulation platform: direct coding (C/C++, Fortran) as well as commercial WWTP simulation software packages can be used. For this reason the full set of equations and all the parameter values are available on this website. Tips for implementation of BSM1 under various platforms are also available in a manual.

The first layout (BSM1) is relatively simple: it combines nitrification with predenitrification, which is most commonly used for nitrogen removal. The benchmark plant is composed of a five-compartment reactor with an anoxic zone and a secondary settler. A basic control strategy is proposed to test the benchmark: its aim is to control the dissolved oxygen level in the final compartment of the reactor by manipulation of the oxygen transfer coefficient, and to control the nitrate level in the last anoxic compartment by manipulation of the internal recycle flowrate. BSM1_LT is based on the same layout but the influent file are longer (609 days) and this benchmark is mainly devoted to long-term assessment on control strategies and faul detection and monitoring.

Schematic layout of BSM1

BSM2 includes BSM1 layout but considers in fact the full treatment of both water and sludge (by anaerobic digestion) with primary settling, thickening and dewatering. Further details can be found on the specific pages of these benchmarks.

The basic procedure to run the benchmark is:

  1. Implement the model equations in the chosen platform
  2. Run the open loop
    • Verify the steady state values
    • Verify the first day dynamics (dry weather)
  3. Tune the controllers
  4. Assess the performances on the basic control strategy
  5. Develop your own control strategy such as respirometry-based control.....

Simulation platform

The benchmarks can be run on any platform. Examples (and tips) of implementation for BSM1 are given in the simulation manual.

Various sections of the benchmark can be updated after a Task Group meeting. Please read carefully the descriptions.

List of publications

A list of publications related to the benchmark is available in pdf:

The benchmark history

Section Last update Comments
Sensors and control handles Feb. 18, 2002

More sensors and control handles have been made available

Manual Sept. 16, 2000

The simulator manual, prepared by John Copp, is now available in pdf

Results Sept. 23, 1999

Summaries of dynamic results collected by U. Jeppsson are available in pdf format


Performance assessment August 19, 1999 B's have been modified
Corrections April 19, 1999 Various updates (steady-state results) and corrections (XND in settler, AE) and additions (influent quality)
Influent files March 12, 1999 Corrected
Performance assessment March 12, 1999 Refined
Biomodel March 12, 1999 hh = 0.8
Operation variables March 12, 1999 Internal recycle flowrate for open-loop assessment
Results Dec 6, 1998 Steady-state and first-day results
Bioreactor Nov 2, 1998 Number of compartments. Have an effect on various related sections
Sludge age Nov 2, 1998 New
Influent files Nov 2, 1998  
Simulation procedure Nov 2, 1998 Stabilisation procedure and open-loop assessment
Average values Nov 2, 1998  
Controllers Nov 2, 1998 Performance assessment (new)
Constrains on manipulated variables Nov 2, 1998 New value for kla
Global performance assessment Nov 2, 1998 Completely reformulated