In-line neutralization of wastewater pH is demonstrated by using a multicomponent process simulator, which includes noise, instrument lags, and six nonstationary parameters. By contrast, the controller action is based on a model that considers the wastewater as a single fictitious acid of unknown concentration and unknown Gibbs free energy of dissociation. Measurable information from a dual base injection is used for a least-squares parameterization of the two-coefficient model. Control over a wide range of wastewater compositions and upsets indicates rapid and effective in-line control without the blending volume required in most pH control strategies.