This paper investigates the development of a simple model for the optimization of codigestion not only using the Biochemical Methane Potential (BMP) but also using the degradation kinetics. This study concerns an experimental work on the implementation and the operation of continuous reactors fed with different fruits and vegetables wastes at different organic loading rates. A simple model was developed dividing the substrate into three fractions of rapidly, moderately and slowly biodegradable organic matter using the biogas production curve from batch reactors. This model was applied to experimental data obtained in continuous mode to test its prediction capabilities: a good agreement between experimental and predicted data was found. Furthermore, the monitoring of the evolution of the different fractions of the substrate over time for continuous operation was carried out. The advantage of this simple model is that it allows optimizing the mix of substrates and determining the organic loading rate at which the available substrate is not completely degraded. In addition, the model makes it possible to monitor the dynamical behavior of each fraction. In parallel, a modified ADM1 model was calibrated using the same data and the same fractionation of the organic matter in three compartments. Satisfying results were obtained, suggesting that the use of the simple model may be useful to identify the different fractions of organic matter and monitor their behavior during co-digestion.