Components and concentrations of the influent stream are often varying in pH processes and changes of components and concentrations alter the nonlinear characteristics of pH processes severely. Hence adaptation coping with such influent stream changes is required for most pH control systems. As in linear adaptive control systems, bursting phenomenon of the estimator is a serious problem in the adaptive control of pH processes. One reliable method avoiding this problem is to excite the process to some extents intentionally. However, it may not be obvious how much the input should be perturbed. Too large perturbation can deteriorate control performances much. To avoid the bursting phenomenon of the estimator without deteriorating control performances, we introduce a small in-line static mixer which is easily implemented and whose output can be excited persistently for the reliable estimation of process parameters. Furthermore, it can be used for the feedforward action to compensate effectively the influent stream changes, which are the major disturbances. Improvements in control performances will justify the additional investment of the in-line static mixer.