Simultaneous model of chlorine dosing and decay in drinking water distribution system and model predictive control application

Abstract

The most commonly applied active disinfectant in drinking water distribution system (DWDS) is free chlorine residual (FCR) in the form of hypochlorous acid and hypochlorite ion. The concentration of FCR decreases along the transport pipeline. Controlled replenishment of chlorine at various sites in DWDS is critical to maintain the FCR in the safe range of 0.2-0.6 ppm. This study proposed a multiple-input multiple-output (MIMO) model (developed in Simulink of Matlab 7.0.1) that simultaneously takes into account chlorine dosing and decay process with the considerations of process disturbances. The model is further implemented into a centralised model predictive control (CMPC) system. The advantages of our CMPC system in controlling multiple outputs are its robustness and short settling time, compared to the conventional process-data-based proportional integral (PI) control strategies. Moreover, the simplicity of this reactive-transport-model-based MIMO control system and the use of Matlab promise an easy adaptation to field test and plant implementation. It addresses an important need in water quality management, particularly for developing countries.