This paper presents both simulation and experimental results for the application of a dual-reagent-injection in-line pH controller for wastewater neutralization The dual-reagent-injection in-line configuration enables the gain estimation of the first-order plus deadtime (FOPDT) model of the process. A proportional-integral (PI) controller is then tuned based on the FOPDT model using Haalman's tuning rules where the process deadtime and time constant are estimated as a function of process flow rates. Controlling the intermediate pH to the average between the inlet pH and effluent pH as well as deadtime coordination of the pH readings greatly enhances the fidelity of the gain of the FOPDT model and the resulting controller performance. The proposed PI-based controller is compared with a fuzzy logic controller, the best control strategy previously developed for this in-line process, and with a conventional PI controller applied to a single-injection process using extreme changes in the influent wastewater character.