Fuzzy Gain Scheduling and Feed-Forward Control for Drinking Water Treatment Plants (DWTP) Chlorination Process

Chlorination in drinking water treatment plants (DWTP) is the final process applied to water before it is sent to storage tanks in the supply network for subsequent human consumption. An excessive dosage of chlorine or, conversely, too small a dosage, may breach existing legal regulations on mandatory limits. Furthermore, excessive amounts generate an unnecessary cost in terms of chlorine and, collaterally, problems due to an increase in the maximum permitted amounts of such by-products as trihalomethanes, which are carcinogenic compounds for humans. In DWTP where there is no significant variability in the quality of the water to be treated, a type of control that is proportional to the flow rate in the effluent can have fully satisfactory results. However, in a control strategy applied when there are inherently long delays in the process, variability in the quality of the water to be treated and considerable variations in flow, a proportional type of control does not tend to work and an alternative type is needed. This article presents the strategy and results of a control method that combines a feed-forward system with gain scheduling in a (Proportional-Integral) PI control. The control system design was validated beforehand by simulation and then applied to a real DWTP, producing satisfactory experimental results.