Process model-based control of wastewater pH

Abstract

Both experimental and simulated control of a highly nonlinear, multi-acid plus common ion salt wastewater flow-through pH neutralization process is demonstrated with a Process Model-Based Control (PMBC) strategy. The reduced phenomenological model of the "expert" controller considers the wastewater as a single fictitious acid of unknown concentration and of unknown Gibbs free energy of dissociation. Measurable process information is used to parameterize the two-coefficient model which is then used to predict a base flow rate set point for conventional PI flow control. PMBC control simulation over a wide range of wastewater composition and upsets indicate rapid and effective control even without the blending volume required in conventional pH control schemes. Although experiments confirm that the strategy works, they also indicate that normal process noise causes a slow response. This document covers the development, dynamic simulation and regulatory PMBC control of discharge pH in a laboratory-scale wastewater neutralization process.