Mathematical modeling of volatile fatty acids production from cheese whey: Evaluation of pH and substrate-inoculum ratio effects

In this work, the pH and substrate-inoculum (S/I) ratio effects on the volatile fatty acids (VFA) production from raw cheese whey were studied. An easily applied mathematical model was proposed to analyze the dynamical behavior of key process variables, allowing the identification of operating conditions that increase the VFA production. The proposed model was developed by considering the hydrolysis and acid-forming stages, and it was adjusted and validated using experimental data obtained in a batch fermenter at different initial pH and S/I ratio conditions. The model parameters were estimated by using the Levenberg-Marquardt algorithm, finding that the estimated kinetic parameters were physical and statistically consistent. Numerical simulations provide the operating conditions where VFA production can be favored, which correspond with those found experimentally, initial pH = 7.0 and S/I ratio of 32.62 gCOD g(VSS)(-1). Therefore, the proposed model might be very useful in predicting the maximum VFA production rate and the maximum organic loading rate (OLR) that could be used without risking the fermentation process stability.