Enhanced biogas production via dual‐layer model predictive control for thermophilic anaerobic digesters

Abstract

Thermophilic anaerobic digestion (AD) is an attractive process due to its higher biogas yield compared to mesophilic digestion. To mitigate its higher heating demand and potential process instability, a dual‐layer control architecture comprising a decision‐making layer and an adaptive model predictive control (MPC) system is proposed. Two specific supervisory layers are designed for startup and demand‐oriented phases. First, a gain‐scheduling supervisory layer generates a trajectory that ensures a smooth transition to steady‐state operation. Second, a demand‐oriented supervisory layer is developed to align biogas conversion into combined heat and power (CHP) with the grid requirements, employing an optimization framework. The underlying MPC layer utilizes an adaptive linear input‐output model to track optimal trajectories while rejecting disturbances. Furthermore, a circular design is integrated wherein the controller stimulates additional biogas production to satisfy internal heating requirements. Simulation results demonstrate that the control system enhances the process performance.