Martijn Devisscher

A simplified method to assess structurally identifiable parameters in Monod-based activated sludge models

The first step in the estimation of parameters of models applied for data interpretation should always be an investigation of the identifiability of the model parameters. In this study the structural identifiability of the model parameters of Monod-based activated sludge models (ASM) was studied. In an illustrative example it was assumed that respirometric (dissolved oxygen or oxygen uptake rates) and titrimetric (cumulative proton production) measurements were available for the characterisation of nitrification. Two model structures, including the presence and absence of significant growth for description of long- and short-term experiments, respectively, were considered. The structural identifiability was studied via the series expansion methods. It was proven that the autotrophic yield becomes uniquely identifiable when combined respirometric and titrimetric data are assumed for the characterisation of nitrification. The most remarkable result of the study was, however, that the identifiability results could be generalised by applying a set of ASM1 matrix based generalisation rules. It appeared that the identifiable parameter combinations could be predicted directly based on the knowledge of the process model under study (in ASM1-like matrix representation), the measured variables and the biodegradable substrate considered. This generalisation reduces the time-consuming task of deriving the structurally identifiable model parameters significantly and helps the user to obtain these directly without the necessity to go too deeply into the mathematical background of structural identifiability.

Control Design of an Industrial Equalization System - Handling System Contraints, Actuator Faults and Varying Operating Conditions

Abstract This paper describes the design and evaluation of a control system for an equalization system at the wastewater treatment plant of a pharmaceutical production facility. The design includes actuator fault tolerance, and measures are included to deal with physical constraints and changing operating conditions. A combination of linear quadratic techniques, fuzzy logic and disturbance accomodation theory is used. The controller is evaluated through simulation and is currently under full-scale test.

COMPARISON OF TWO ADVANCED CONTROL STRATEGIES FOR MONITORING OF ACTIVATED SLUDGE PROCESSES

Abstract : This paper deals with the comparison between two control strategies for the optimal operation of Activated Sludge Processes (ASPs). The first approach describes an industrial control strategy composed of two decentralized Proportional Integral controllers (PIs) while the second approach is based on a state space model of the system together with the Disturbance Modeling Principle (Johnson, 1976). It is shown that if the second approach needs additional sensors than the first one, when implemented properly, it allows the user to estimate unknown inputs that can be useful for diagnosis purposes. Simulation results are provided before some conclusions are drawn.