A fuzzy logic controller of two-position pump with time-delay in heavy metal precipitation process

The process control of pH in wastewater neutralisation and metal precipitation processes has been identified difficult to achieve via a normal conventional PID controller due to its non-linear and time-varying characteristics. Recently, controlling pH via fuzzy logic system that makes use of uncertain information and valuable human experience, has gained new attention and been proved efficient in controlling pH. Normally, in fuzzy logic controller, the speed of variable speed pumps are varied according to fuzzy rule base, in order to control the addition of caustic solution in metal hydroxide precipitation. However, in Malaysia, most of the small and medium scale industries are still using traditional instruments of on-off pumps (also known as two-position pumps) in controlling their processes. The management are reluctant to purchase new variable speed pumps due to the high cost constraint. The aim of this study was to develop a low-cost and reliable fuzzy logic pH controller, by making use of the traditional pumps. A set of fuzzy rules was developed based on two controller inputs, error (e) and change of error (Δe). Instead of pump speed (u), time-delay in switching on or off the pumps is used as the controller output in order to control the addition of caustic solution. The fuzzy logic controller successfully increased the pH of acidic wastewater to pH 9 and maintained this pH for all runs regardless the initial metal concentration of the wastewater. The results proved that the fuzzy concept is still applicable and yet, the present instruments can be used.