Adaptive Control of a Waste Water Neutralization Process

Abstract

The paper describes a new method for adaptive pH control of a continuous neutralization process in a waste water treatment plant. Due to space limitations and other process reasons the neutralization takes place in a small reactor with low residence time and thus fast dynamics (dominating time constant 30 sec). The waste water feed is collected from different pilot plants and production plants. The composition and the concentration of the waste water and thus its nonlinear titration curve vary fast. In this case neither conventional PID control nor feedforward control based on titration measurement nor adaptive control based on recursive identification can be applied due to the fast variations of the process parameters and the large disturbances acting on the process. In order to overcome these problems a new adaptive control concept has been developed where the main control loop is governed by an additional adaptive control loop. This adaptive control loop manipulates the gain of the main control algorithm so that in the case of a control deviation the pH of the effluent stream approaches its setpoint (e.g. the neutralization point) by following a prescribed trajectory. This adaptive control system is implemented on a microcomputer, and many experiments have proven its very good practicability for a large class of disturbances.