Cadmium concentration stabilization in a continuous sulfate reducing bioreactor via sulfide concentration control

Abstract

AbstractCadmium concentration stabilization in a single input-single output continuous bioreactor via sulfide concentration, as the controlled and measured output state variable, was assumed. For the above process, a novel kinetic model of the sulfate-reducing process for cadmium removal was proposed and experimentally confirmed. This model has been extended to continuous operation, which is employed as a virtual plant to enable the implementation of the proposed controller. The considered nonlinear control law contains a sigmoid feedback of the given control error in order to regulate the sulfide concentration at the maximum value indirectly leading to cadmium concentrations meeting the environmental regulations. A theoretical frame of the closed-loop stability of the bioreactor is provided under the assumption that bounded trajectories occur in the bioreactor. Finally, numerical experiments proved satisfactory performance of the proposed methodology in comparison with the standard sliding-mode and linear PI controllers.