This work describes a novel approach to the theoretical prediction of optimal pH values of critical importance to the efficiency of a number of wastewater treatment processes such as precipitation, coprecipitation, coagulation, flocculation, adsorption, oxidation and reduction. The developed equlibrium pH modelling approach is comprised of selecting the appropriate representative equlibrium data among other complex equlibria which is key to the prediction of the optimal pH under investigation, and subsequently solving the algebraic or differential hydrogen ion-dependent equation resulting from this evaluation. This approach has been applied to environmental problems such as minimum solubility of boehmite, phosphate precipitation by ferric and aluminium salt flocculants. lime-sulfide treatment of zinc ion containing wastewater. silver ion precipitation from photographic effluents, and isoelectric pH of hydrous ferric oxide in the absence and presence of chromate.