Conducted and Current Research topics

1. Control strategies for the activated sludge process
2. A software sensor for determine the respiration rate and oxygen transfer rate in an activated sludge process.
3. Design of a control and supervision system for an activated sludge process.
4. A simulator for the activated sludge process.
5. Modelling of the activated sludge process by linear regression techniques such as principal component analysis and partial least squares.
6. Many of the suggested strategies are evaluated in a pilot-scale plant located at the main municipal wastewater treatment plant in Uppsala.

Control strategies for the activated sludge process

• A nonlinear dissolved oxygen controller. A strategy for designing a nonlinear DO controller has been developed. The basic idea was to take the nonlinear oxygen transfer function into account in the controller design. Simulations and pilot-scale plant experiment have illustrated that a nonlinear DO controller outperforms a standard PI controller.
• Furthermore, we have evaluated the use of an autotuning controller for controlling the dissolved oxygen concentration (DO) in the full scale municipal wastewater plant in Uppsala.
• The concept of feedforward control has a large potential to be more used in WWTP's. In particular the use of upstreams measurements can be useful to quickly react to load disturbances. One example is to use feedforward control for accurate dosing of an external carbon source. An adaptive feedforward/feedback carbon dosage controller has been developed, see figure below.
  
  Currently the strategy is evaluated in a pilot-scale plant, unfortunately without feedforward sensors.
• We are also planning to use process knowledge in terms of, for example, experience data bases for developing novel control strategies.
• Extremum and supervision control. In order to optimize the plant performance it is crucial how the set-points are selected for the unit process controllers. A strategy based on controlling the effluent ammonia concentration by DO set-point control has successfully been used in a pilot plant. Further strategies are under development.

A software sensor for determine the respiration rate and oxygen transfer rate in an activated sludge process.

• A software sensor for respiration rate and oxygen transfer rate have been developed. The software sensor utilizes measurement of air flow rate and dissolved oxygen and consists of a Kalman filter type estimator.
  
  In the estimation scheme the time varying respiration rate was modelled by a filtered random walk model, and the nonlinear KLa function was modelled with an exponential model. A numerical study illustrated the advantage of the method. Also, real data were applied to the software sensor with promising result.
• A filtering procedure was applied for the case when the DO sensor dynamic can not be neglected. This filter can be applied to all sensors which has dynamics.

Design of a control and supervision system for an activated sludge process.

• The design of control and supervision system is an important factor in increasing the automation in a WWTP. It is obviously important to have a user friendly user interface. Also, it should be possible to easy implement advanced control and signal processing strategies. A novel design and implementation of a computerized control and supervision system was developed. Much of the programming effort was made as a master thesis work by Mr Jouko Latomaa. Here is an example of the graphical interface. This system is currently used in a pilot plant activated sludge process. Current work is concerned with further development of the system both in terms of user interface design and portability.

A simulator for the activated sludge process.

• In an ERASMUS project, Mr Joerg Luttmer has developed a simulator for the activated sludge process. The IAWQ model no 1 is used as the general process model. The same interface which is used in the computer controlled system described above is used in the simulator. This gives a quite realistic simulation environment which may be valuable in education and training of operators and general simulation studies.