This paper presents an indirect adaptive control scheme for a pH process, which is difficult to control due to its nonlinear dynamics with uncertainties. A nonlinear controller is designed using a backstepping technique, which can deal with a large class of nonlinear systems with parametric uncertainties. The nonlinear controller is combined with a parameter estimator to estimate the concentrations of the reaction invariants in the wastewater stream, and the stability of the proposed adaptive scheme is proved. Simulations show that uniform closed-loop performance is obtained despite the nonlinearitics and parametric uncertainties.