Adapting R4 simplifications of Anaerobic Digestion Model No. 1 (ADM1-R4) for pump-mixed biogas production

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Modification of the production chain in biogas generation is a common tactic used in this industry. However, the selection of appropriate reactor configuration and operational parameters is a crucial task. In such cases, mathematical modeling provides great support. Herein, we adapted a simplified version of the Anaerobic Digestion Model No. 1 to a system in which the mechanical stirrer was replaced with an external pump that recirculated the reactor content. Despite having conceptual similarities with continuous stirred-tank reactors, this system exhibited considerable differences in the vertical distribution inside the tank. The model was optimized by using a “genetic algorithm” and “fmincon” function to test both approaches. The new model showed very high accuracy with a mean error of 5.9–9.8%, depending on the mixing intensity, whereas the previous reference models reached 19.7% error. Therefore, compared to the previous models, the simplification of the ordinary differential equation in our new model did not significantly decrease accuracy; in fact, the precision was even higher than before in some cases. Finally, the new model was practically applied to demonstrate its implementation in realistic scenarios.