The control of waste water operating parameters, especially pH, had long been regarded as a difficult task. This difficulty arises from its severe process non-linearity, tremendous dead time and frequent load changes, such as changes in the influent composition and flow rate. The non-linearity can be seen from the S-shaped static pH responses with the addition of titrant where the process gain is low in the buffered zone and extremely high around the neutrality point. In order to make the pH control effective, for example, we need a controller which is rapid in the buffered zone with large controller gain and sensitive around neutrality (pH 6-8 where that is a sudden change from acid to base condition). The controller gain in this region must be small enough in order to maintain a constant gain in the feedback loop to avoid sustained oscillation around the set-point. This difficulty have led to the various alternatives being introduced to solve the problems, such as predictive combined with traditional control, such as modified PI controller, adaptive control, predictive-adaptive control, fuzzy logic and gain scheduling. In this study, a relay feedback auto-tuning controller is used to regulate the pH. The auto-tuner will excite the process output into limit cycles from where the ultimate gain and period can be determined. The PID values can be calculated based on these parameters and imparted to the controller.