With the objective of contributing to the buildup of mathematical tools for anaerobic process simulation, an algorithm for the dynamic simulation of pH was developed. The dynamic simulation of the gaseous phase variables was also considered. The pH algorithm was validated for a watery system, obtaining good agreement between predicted and experimental data. The applied methodology provides a differential equation that allows the inclusion of pH as a state variable of the system that can be easily included in a general mathematical model of anaerobic digestion using matrix notation. This methodology also allows a noticeable decrease in computing time in simulations. A dynamic anaerobic digestion model of complex substrates taken from the literature was completed with the developed algorithms, and it was used to predict the response of an anaerobic reactor against overloading and against the presence of pH-dependent inhibitors with satisfactory results.