Benchmark

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.

The COST 682 Working Group No.2 has developed a benchmark for evaluating by simulation, control strategies for activated sludge plants. The benchmark development is now undertaken by all the COST 624 Working Groups, in function of their specifities.

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 the COST 624 website (http://www.ensic.inpl-nancy.fr/COSTWWTP).

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.

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 benchmark can be run on any platform. Examples (and tips) of implementation are given in the simualtion manual.

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

List of publications

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

B'02

The next IFAC (Internation Federation of Automatic Control) World Congress will take place in Barcelona (Spain) from July 21 to 26, 2002 B'02. An invited session with presentations of control strategy behcnmarking has been set-up and accepted