MIMO sliding mode control of a distributed parameter denitrifying biofilter

In this paper, the control problem of a distributed parameter system is developed. The process considered is a fixed bed reactor in which drinkable water is treated. Micro-organisms fixed in the reactor absorb the harmful components in such a way that their concentrations decrease in the outflowing water. The addition of a carbon source is needed in this operation. The complexity of the control problem is due to the distributed and nonlinear nature of the model having time varying biological parameters. In drinkable water the harmful components are supposed to be nitrates, nitrites and ethanol supplied in the reactor inlet. The main contribution of this paper consists of designing a multi-input/multi-output (MIMO) sliding mode control of the distributed parameter biofilter. Two approaches are developed: early lumping and late lumping sliding control. In both cases, not only are the harmful component concentrations controlled but moreover the addition of the carbon source is determined in such a way that the quality of water fulfils international standards, The performances of the two approaches are compared and illustrated by means of simulations. (C) 2001 Elsevier Science Inc. All rights reserved.